ARTEMIS MISSION MODIFICATIONS FOR PLANETARY SCIENCE

A PROPOSAL SUBMITTED TO:

MISSION OPERATIONS AND DATA ANALYSIS PROGRAM

FOR THE

PLANETARY OPERATING MISSIONS

AUGUST 22, 2009

V. Angelopoulos, THEMIS Principal Investigator, University of California

D. G. Sibeck, THEMIS Project Scientist, NASA/GSFC

J. Halekas, G. T. Delory, R. Lillis, Space Sciences Laboratory, University of California, Berkeley

C. T. Russell, K. Khurana, G. Schubert, Institute of Geophysics and Planetary Physics, UCLA, and

R. E. Grimm, Department of Space Studies, Southwest Research Institute, Boulder ARTEMIS MISSION MODIFICATIONS FOR PLANETARY SCIENCE

1. EXECUTIVE SUMMARY ...... 1 2. ARTEMIS (P1 AND P2) CONCEPT...... 3 3. PLANETARY SCIENCE WITH ARTEMIS...... 5 3.1 EXOSPHERE AND PLASMA PICK-UP ...... 8 3.2 LUNAR DUST...... 10 3.3 DUST TRANSPORT ...... 12 3.4 INTERIOR STRUCTURE AND COMPOSITION OF THE MOON FROM ELECTROMAGNETIC INDUCTION...... 12 3.5 SURFACE PROPERTIES AND PLANETARY EVOLUTION AS REVEALED BY CRUSTAL MAGNETISM AND SPACE WEATHERING...... 15 3.6 ARTEMIS AND LRO...... 18 3.7 ARTEMIS AND LADEE...... 19 3.8 ARTEMIS AND INTERNATIONAL LUNAR NETWORK...... 19 4. PLANETARY SCIENCE TRADE STUDIES...... 19 4.1 PERISELENE REDUCTION...... 19 4.2 INCLINATION ADJUSTMENTS...... 20 4.3 INSTRUMENT PLANETARY RATES AND MODES ...... 20 5. INSTRUMENT OPERATIONS FOR PLANETARY...... 20 5.1 PARTICLE INSTRUMENT MODE CHANGES ...... 20 5.2 MAGNETOMETER NOISE REMOVAL ...... 21 5.3 SHADOW SPIN RATE CHANGES ...... 21 6. MISSION OPERATIONS: STATUS AND PLANETARY TASKS...... 22 6.1 OBSERVATORY AND INSTRUMENT STATUS ...... 22 6.2 STATUS OF GROUND SYSTEMS ...... 23 6.3 PRIME MISSION OPERATIONS (FY07/08/09) ...... 23 6.4 TRANSLUNAR PHASE (FY10) ...... 23 6.5 LISSAJOUS PHASE (Q1,Q2 OF FY11)...... 24 6.7 LUNAR ORBIT (LO) PHASE ...... 24 6.8 ARTEMIS MISSION DESIGN AND NAVIGATION ...... 25 6.9 ARTEMIS FLIGHT OPERATIONS AND SCHEDULING ...... 25 6.10 SUMMARY OF MISSION OPERATIONS TASKS ...... 25 8. PRIOR RESULTS, COMMUNITY SUPPORT ...... 26 9. PUBLIC AFFAIRS AND EPO ...... 27 9.1 RECENT PUBLIC AFFAIRS ACTIVIVIES ...... 27 9.2 EPO PLANS...... 28 10. REFERENCES (TERSE)...... 28 11. ACRONYMS...... 30 ADDENDUM: EXPANDED REFERENCE SECTION...... 31 1. Executive Summary reduce operational complexity. As a result, the probes have orbital and attitude configurations resulting in an ARTEMIS, a two satellite mission to the Moon, operational environment (thermal, power) very similar provides entirely new scientific objectives for the two to that at Earth. Inter-probe separations varying from outermost THEMIS probes. THEMIS, a MIDEX-class 100’s of km to 20RL at lunar distances will enable heliophysics mission comprising five identical probes P1 and P2 to make the first systematic two- satellites (“probes”), was launched on February 17, point observations of distant magnetotail phenomena, 2007 to study magnetospheric substorms, solar wind- with the comprehensive instrumentation needed to magnetosphere coupling and radiation belt electron resolve outstanding heliophysics questions concerning energization (Angelopoulos, 2008). By September not only solar wind and magnetotail phenomena, but 2009, THEMIS will have successfully completed its also the structure and dynamics of the lunar wake at primary objectives, returning observations that are downstream distances ranging from 100s of km to already changing our understanding of magnetospheric 30RL. The Heliophysics Senior Review panel strongly processes. In its proposal to the February 2008 endorsed the ARTEMIS mission concept (although the Heliophysics Senior Review, the THEMIS team funding allocated fell significantly below that proposed an extended mission retaining the three requested), and ARTEMIS operations commenced in innermost probes, P3, P4 and P5, in Earth orbit while the summer of 2009. After several lunar and Earth sending the two outermost probes, P1 and P2, into flybys in early 2010, the ARTEMIS probes are lunar orbit. The rationale for the ARTEMIS concept expected to enter through a low-thrust trajectory the was to conduct cutting-edge heliophysics science with Earth-Moon Lissajous orbits in October 2010 and be the outermost two probes and simultaneously evade inserted into stable, low inclination, highly eccentric terminal shadows anticipated in March of 2010 if the lunar orbits in April 2011. Heliophysics operations spacecraft remained in Earth orbit. Thus ARTEMIS have been approved through 2012. was born, to study “Acceleration, Reconnection, Turbulence and Electrodynamics of Moon’s Interaction with the Sun”. The two ARTEMIS probes, now en-route to the Moon, will be captured into Lunar orbits in April 2011.

Figure 1.2 ARTEMIS will study with two identical, cross- P1=TH-B calibrated spacecraft lunar exospheric ions and dust, crustal P2=TH-C magnetism, and the lunar interior. One probe will measure P3=TH-D the pristine solar wind driver, while the other will study the P4=TH-E lunar environment’s response. ARTEMIS extends the P5=TH-A SELENE/Kaguya results into the next decade, while it provides synergy with LRO, LADEE and the International Figure 1.1. THEMIS extended baseline and ARTEMIS. Lunar Network. Insert shows probe number assignments to probe letters,

which was done after early checkout. Orbits are publicly From the moment ARTEMIS was conceived, the available for plotting at: http://sscweb.gsfc.nasa.gov/tipsod team realized that significant benefits to planetary For ARTEMIS: ART_1,2; for the Moon click on: “Moon”, and science could accrue from the two lunar probes with for THEMIS P3, P4 and P5 select THEMIS_D,E,A (pred). further, albeit small, orbit and instrument

optimizations. Aside from the significant progress JPL mission designers and the ARTEMIS science expected in understanding the lunar wake and team have optimized the ARTEMIS orbits for radiation hazards at the Moon’s orbit (of interest to heliophysics science over the last 3 years. The orbits both Planetary and Heliophysics), ARTEMIS can were designed to be stable over several years and to address fundamental questions at the forefront of

1 planetary science at the Moon (Figure 1.2): the sources NOVA, Discovery and PBS, as well as the top 10 and transport of exospheric and sputtered species; the science stories in Astronomy Magazine. Our charging and circulation of dust by electric fields, the experienced Education and Public Outreach team has structure and composition of the lunar interior by already established a vigorous program linked to electromagnetic sounding; and the surface properties museums and schools around the country to and planetary history, as evidenced in crustal disseminate the findings from ARTEMIS, excite magnetism. Additionally, ARTEMIS’ goals and young minds about planetary science, and bring the instrumentation complement LRO’s extended phase inspirational can-do attitude of ARTEMIS directly to measurements of the lunar exosphere and of the lunar classrooms, with particular emphasis on under- radiation environment by providing high fidelity local represented schools. solar wind data. ARTEMIS’ electric field and plasma The same high quality data, analysis code, and data also support LADEE’s prime goal to understand documentation the team employs are routinely exospheric neutral and dust generation and transport. available on the web (http://themis.ssl.berkeley.edu/) The ARTEMIS implementation team has already and will be mirrored to a dedicated, ARTEMIS web demonstrated that cleaning up minor instrument noise, page. The data are also served via an increasing an essential step in preparing the payload for the low number of mirror sites (France, Japan, Canada). A magnetic field, low particle flux lunar environment, is dedicated ARTEMIS help line will be available at feasible. The health of the instruments is excellent, as “[email protected]”, and evidenced by numerous discoveries from the prime updates will be announced through the “ARTEMIS- mission (see Section 8). THEMIS is the first mission science-support-announce” mailing list. THEMIS to ever boast flawless instrument behavior on five already conducts well-attended software demos and satellites after 2.5 years in orbit. ARTEMIS’ state-of- training sessions, paving the way for similar the art electron and particle detectors match or exceed ARTEMIS sessions at major planetary meetings. The electron reflectometry capabilities of Lunar ARTEMIS data are already SPASE-compatible, are Prospector. High sensitivity, well-characterized available through Virtual Observatories (VxOs), and magnetometers, electric field, and energetic particle will transition seamlessly into the Planetary Data instruments are ideally suited for the low field, low System (PDS) at UCLA. count lunar environment. ARTEMIS will provide the Adjusted ARTEMIS orbits will generate dozens of first simultaneous, comprehensive in situ low altitude periselene passes (~100km) and hundreds measurements from locations near the lunar surface of out/inbound passes through the lunar exosphere and and in the nearby pristine solar wind with identical, wake at altitudes ranging from 100 to 10000km. The cross-calibrated instrumentation. orbits are ideal for remote sensing the lunar interior The team has demonstrated that the periselene and crust, as well as exospheric species picked up by altitude of the two probes could be reduced to ~100km the solar wind. Stable for at least a decade, ARTEMIS or less (depending on stability) by expending some of will monitor exospheric constituents and surface the available fuel margin. The team also anticipates properties of the Moon over solar-cycle time-scales, that by re-optimizing the lunar orbit insertion, it will and establish a lunar environment database in advance can achieve a higher inclination orbit (goal ~ 20°) with of increased human presence on the surface. manageable stationkeeping fuel requirements. As was ARTEMIS is timely: on the heels of the exciting the case for the heliophysics optimization of the discoveries from SELENE/Kaguya on lunar mission design, adjusting the mission to address exospheric composition and transport, it possesses in planetary science will result in maximum science yield situ instrumentation that overlaps and complements for the Planetary Division’s investment from a frugal, Kaguya’s capabilities (e.g., both missions have operational plan. Designing the mission requires active particles and magnetic field, but ARTEMIS also has involvement of an expert planetary science team and DC electric fields and electromagnetic waves, whereas attention to operational and mission resources. Kaguya had a remote sensing package). ARTEMIS THEMIS discoveries, including initiation of overlaps LRO’s extended phase investigation and substorm surges in the magnetotail by magnetic LADEE’s prime investigation. It will extend Kaguya reconnection, identification of the source of hiss measurement capabilities in the LRO and LADEE era waves at the heart of the radiation belts, and first and will provide important synergies with current and detection of dayside chorus waves at quiet times, future missions, such as the International Lunar herald the team’s and the instrumentation’s potential Network of geophysical nodes, in need of an ambient for similar discoveries in the lunar environment from a magnetic field monitor from lunar orbit. planetary perspective. These science successes have been well covered by the press and electronic media, including CNN’s most popular science stories,

2 ARTEMIS is an interdisciplinary mission of contribute greatly to our understanding of the discovery: Not only does it address key Planetary and formation and evolution of the exosphere, dust Heliophysics science questions of the Moon and From levitation by electric fields, the crustal fields and the Moon, but it is responsive to the Vision for Space regolith properties and the interior of the Moon from Exploration by enabling continuous monitoring of the the achievable 100km perigee altitude, ~10° lunar radiation environment and exosphere and by inclination orbit. By optimizing periselene to obtain being the first to use operationally the Earth-Moon low altitude passes below 100km and inclinations as Lissajous orbits, thus becoming a test-bed for future high as 20° with a goal to reach the outskirts of the lunar relay stations and lunar landing staging grounds. South Pole – Aitken basin, the ARTEMIS team can The proposed investigation is directly aligned with maximize the science return from the mission for the findings of the National Research Council’s Planetary science, without any adverse effect on the (NRC’s) 2003 Decadal Survey on “New Frontiers in heliophysics mission objectives. ARTEMIS the Solar System, An Integrated Exploration instruments (Figure 2.1, Table 2.1, or Table VI in Strategy”, which proclaimed the Moon as a high Angelopoulos, 2008 for a detailed synopsis) can priority target for inner planet research. This is due to provide magnetic field, electric field, and particle the special importance the Moon had in shaping our distributions with state-of-the-art cadence, offset planet’s past and the critical information it holds about stability and sensitivity. Orbit and instrument the evolution of all the rocky planets. Amongst the top optimization to address Planetary objectives can start lunar science goals of the NRC Decadal Survey were immediately, be tested on flybys, and be in place by the “determination of the [Lunar] internal structure, … lunar orbit insertion in April 2011. and possible existence of an iron-rich core” (p. 62), both related to the goals of the ARTEMIS investigation. By funding ARTEMIS to conduct Planetary research, NASA expands the frontiers of knowledge in planetary science, advances lunar exploration in a novel and efficient manner and provides cross-disciplinary benefits for NASA Science.

2. ARTEMIS (P1 and P2) Concept The “Acceleration, Reconnection, Turbulence, and electrodynamics of Moon’s Interaction with the Sun” (ARTEMIS) mission uses two-spacecraft (“probes”) currently en route to the Moon. The mission has been optimized to address heliophysics questions related to acceleration, reconnection and turbulence in the (i) magnetosphere and (ii) the solar wind, and (iii) the electrodynamics of the lunar environment. From distances 100km to 120,000km from the Moon and at variable inter-probe separations optimized for heliophysics science, the two ARTEMIS Figure 2.1 One of two ARTEMIS probes shown with probes will address fundamental questions related to its instrumentation, in deployed configuration. The the dynamics, scale size, and evolution of distant tail fields of view of the body-mounted particle instruments and solar wind particle acceleration and turbulence are highlighted. The spin-stabilized probe provides processes and the kinetic properties of the lunar wake. three dimensional particle information once per spin The probes are expected to reach Lissajous orbits (the period (Tspin=3s). Electric Field Instrument spin plane Lagrange points of the Earth-Moon system) in October booms (EFIs) are 40m long and 50m long tip-to-tip 2010 and enter into lunar orbits in April 2011 (see wire dipoles. EFIa (axial) stacer booms are ~7m tip- Table 2.2, Figure 2.2). to-tip. FluxGate Magnetometer sensor (FGM) and ARTEMIS’s multi-point observations, orbits, and Search Coil Magnetometer sensor (SCM) are mounted instrumentation are also uniquely suited to advance on 2m and 1m graphite epoxy booms. our knowledge on several key topics raised in the 2003 NRC Decadal Survey for Solar System Exploration History: Late into the THEMIS mission’s and several prioritized science concepts listed in the development cycle the team recognized that Earth 2007 NAS report “The Scientific Context for shadows exceeding the bus design limit would Exploration of the Moon”. Specifically, with all its threaten THEMIS probes P1, P2 during their third tail instruments operating flawlessly, ARTEMIS can season (one year after the prime mission was over).

3 Additionally, the angles between the lines of apsides Lunar Libration points LL2 and LL1 respectively, o o for P1 and P2 would be 54 and 27 away from those resulting in 10-20 RE separations (LL1,2 phase) along of P3, 4, and5, rendering five-probe conjunctions less and across the Sun-Earth line (Figure 2.2). After 3 than optimal. It was recognized that by placing P1 and months P1 is brought onto the same side of the Moon, P2 into stable lunar orbits, their potential for scientific (LL1 Phase) resulting in smaller, 5-10RE separations. discovery would be maximized for heliophysics, while After another 3 months, both probes are inserted the risk of freezing would be avoided. This formed the into stable, ~300km x 19000km (heliophysics plan), genesis of both the ARTEMIS concept and the equatorial, ~1-day period lunar orbits with separations ARTEMIS science team. Orbits have been optimized ~500km - 5RE (LO Phase). P1 is on a retrograde and for maximum Heliophysics science in collaboration P2 on prograde orbit, resulting in a fast, 360o relative with JPL since 2005, and were vetted with the precession during the 17 months of this phase for ARTEMIS team on three THEMIS Science Working heliophysics science objectives – this aspect of the Team meetings. A series of technical reviews held at mission will also be retained. It is evident that the GSFC and at JPL, and a formal technical review at probe separations become progressively shorter as the GSFC in February 2009 further strengthened the probes move from one mission phase to another. ARTEMIS technical implementation, which Since the Moon visits the magnetotail and solar commenced with orbit raise maneuvers on the day of wind once each 28 days, the two probes measure the the 40th anniversary of NASA’s lunar landing, July response of the lunar environment under different 20th 2009. The first three lunar flybys are expected in drivers during each phase of the mission. Furthermore, January-March of 2010. as the probes travel around the Moon, they sample the Instrument Specs Reference exosphere and near-equatorial surface from a variety FGM: DC Magnetic Field of altitudes and solar zenith angles. As of this FluxGate Frequency: DC-64Hz Auster etal., 2008 Magnetometer Offset stability <0.2nT/12hr proposal, the ARTEMIS mission has been vetted by SCM: several technical reviews and is en route to lunar AC Magnetic Field Roux et al., 2008 SearchCoil Frequency: 1Hz – 4kHz LeContel et al., 2008 gravity assists in the Fall of 2009, and translunar Magnetometer injections in 2010 that will eventually bring P1 and P2 EFI: 3D Electric Field Bonnell et al., 2008 into lunar orbit. The first datasets to be recovered from Electric Field Frequency: DC – 8kHz Cully et al., 2008 Instrument the proximity of the Moon will occur during lunar Total ions: 5eV – 25 keV flybys in late 2009 and early 2010 (closest approach = ESA: Electrons: 5eV – 30 keV 2.89RL on a polar Sun-Moon plane pass); these will Electrostatic g-factor/anode: McFadden et al., 2008 guide science orbit and instrument optimization, as Analyzer -ions: 0.875x10-3cm2str -electrons: 0.313x10-3 cm2str well as data processing and science validation plans SST: Angelopoulos, 2008 over the next year in anticipation of lunar orbit Total ions: 25keV – 6MeV Solid State for mounting, and Electrons: 25keV – 1 MeV captures in 2011. Telescope fields of view. Table 2.1 THEMIS instruments and their capability Mission Phases: After trans-lunar injection (TLI phase), P1 and P2 are captured into opposite Earth- Time Phase Abbr ARTEMIS: probes P1, P2. Heliophysics Objective Planetary Objective Interval Translunar Oct. ’09- Translunar orbits to capture into Lunar Flybys: Build Lunar Flybys: Build tools, TLI Injection Oct. ’10 LL1,LL2 tools, experience experience dR =20R at Moon P1 at LL2, LL1,2 Oct. ’10- P1-P2 E At Solar Wind (SW) wake or dRP1-P2 along/across Wake & Sun-Earth P2 at LL1 Phase Jan. ’11 GSE GSE In the Magnetotail: downstream: Pickup ions? dX ~ dY ~ 500km-20R P1-P2 P1-P2 E Rx, SW-magnetosphere P1,P2 at dR =5-20R at Moon LL1 Jan. ’11- P1-P2 E interaction, tail At Solar Wind (SW) wake or Lunar dRP1-P2 along/across Wake & Sun-Earth Phase Apr. ’11 GSE GSE turbulence downstream: Pickup ions? Libration 1 dX ~ dY ~ 500km-20R P1-P2 P1-P2 E In the Solar Wind (SW): Foreshock, shock In the Solar Wind (SW): acceleration, Wake/downstream: pickup ions. dRP1-P2=500km-20RL at Moon Rx, SW turbulence Periselene wake: Crust, Core dR along/across Wake & Sun-Earth Periselene dayside: Dust In Lunar LO Apr.’11- P1-P2 In the Wake (SW or Tail) Periselene = ~ 100 km [trade TBD] Magnetotail: orbit Phase Sep. ’12 Kinetics and dynamics of Aposelene = ~19000km lunar wake in SW, Crust, mini-magnetospheres, core Inclination = ~10deg [trade TBD] sheath, tail Periselene dayside only: Magnetotellurics, Dust

Key: T=Tail; Rx= Reconnection; RL =Lunar radii = ; RE =Earth radii Table 2.2: ARTEMIS (FY10-12) Orbits and Mission Phases Versus Heliophysics and Planetary Objectives

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– Along/Across Sun-Moon Line (ΔR:500km–5 RE) –Along/Across Sun-Earth Line (ΔR: 10 – 20 RE) – Along/Across Sun-Earth Line (ΔR: 5 – 20 RE) – Lunar Wake (Traversals at 10-30R ) – Lunar Wake (Traversals at 10-30R ) – Lunar Wake (Traversals at 100km-10RL) L L

Figure 2.2. ARTEMIS by phase (Phases LL1,2 and LL1 are shown in GSE coordinates. Phase LO is shown in Selenocentric Solar Ecliptic, SSE, coordinates. Acronyms in Table 2.2). P1 is red, P2 is green and the Moon gray. Phases are designed to permit progressively smaller inter-probe separations in all regions visited. These orbits are publicly available for plotting at: http://sscweb.gsfc.nasa.gov/tipsod . For probes P1 and P2 select: ART_1 and ART_2; for the Moon select: “Moon”.

3. Planetary Science with ARTEMIS Since 2003, the time of the last NRC Decadal Survey, several international and US lunar missions The inner planets (Mercury, Venus, Earth and the have been launched (SMART-1, SELENE/Kaguya, Moon) hold critical information regarding the origin Chang’e, Chandrayaan-1, LRO and LCROSS) and of the solar system and habitable environments two are currently in the planning for launch in 2011- within it. The Moon, together with Mercury, 2012 (GRAIL and LADEE). The 2007 NRC study on preserves records of past events which have been “The Scientific Context for Exploration of the Moon” largely erased on Earth and Venus. A witness to 4.5 (herein refered to as “SCEM”) incorporated the billion years (Ga) of solar system history, the Moon’s results and expectations from the current lunar surface has recorded that history more completely missions, addressed the scientific challenges and and preserves it more purely than any other planetary opportunities in the period 2008-2023, and put forth a body, since it is devoid of Earth-like plate tectonics, set of goals and recommendations independent of Venus-like planet-wide volcanism, and Mars-like programmatic implementation but also are on par surface-altering atmospheric processes. with NASA’s Vision for Space Exploration. Intended The layering of the lunar interior preserves for near-term guidance to NASA, NRC’s records of the differentiation of planetary bodies in recommendations were prioritized by three criteria: the early solar system. Understanding of the lunar scientific merit, opportunity and technological surface and the stratification of the lunar interior readiness. The top eight science goals were provides a window into the early history of the Earth- prioritized and discussed in Table 5.1 of the NRC Moon system, and can shed light on the evolution of report. Since the report, NASA mission LADEE has other terrestrial planets such as Mars and Venus. been accepted for flight in 2012, aimed at studying In 2003, the National Research Council’s Decadal the lunar exosphere with in-situ instrumentation from Survey on “New Frontiers in the Solar System, An low altitude, and ARTEMIS has been approved to Integrated Exploration Strategy” identified the commence ascend operations to conduct critical importance of understanding: (1) the core, Heliophysics observations around the Moon. mantle and crust evolution, and the characteristics of Moreover, the Japanese mission SELENE/Kaguya’s the metallic core of inner planets; (2) the history and results on the lunar exosphere have reshaped our role of early (3.8-4.5 Ga) meteoritic impacts and (3) understanding of lunar atmosphere populations and the history of water and other volatiles at inner interactions with the surface and the environment, planets. The Moon specifically and its South Pole- sparking renewed interest in conducting planetary Aitken Basin in particular were singled out as high- science via remote sensing of exospheric and surface return targets for further studies and for sample charged particle populations, and paving the way for return, in order to address these questions, since ARTEMIS. Equipped with charged particle detectors understanding our closest planetary body and the and electromagnetic sensors, ARTEMIS will make chronology of its oldest large crater exposing significant contributions to 4 of the top 8 lunar material elevated from the early lunar mantle holds science goals identified in the NRC report, as shown clues on inner planet evolution and differentiation. in Table 1. At the same time it will provide

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synergistic information to the extended LRO mission, magnetic fields and measured particle populations far and the upcoming LADEE mission. from the source. ARTEMIS will use its energy-angle spectroscopic capability and its full electric and ARTEMIS Science Goals Primary relation to NRC magnetic sensors to determine motion, source and and Means prioritized concepts flux of exospheric ions. Additionally, dust particles A. Sources and transport of exospheric and sputtered SCEM# 8. Processes involved are controlled (i.e., lofted and transported) by surface species, in relation to with the atmosphere and dust electric fields, which can be remotely sensed using surface features, as revealed environment of the Moon, electron reflectometry or measured directly from in the charged particle accessible while the altitude. ARTEMIS will use its unique environment environment remains in a B. Dust charging and pristine state. electromagnetic field measurements to determine the circulation by electric fields. forces acting on dust populations and their C. Structure and SCEM # 2. The structure and acceleration and deposition or loss in the lunar composition of lunar interior composition of the lunar interior environment. The ARTEMIS dataset of solar wind, as revealed by provides fundamental exospheric species and electromagnetic fields will electromagnetic sounding information on the evolution of a from orbit. differentiated body. provide important synergies to LRO’s UV SCEM # 3. Key planetary spectroscopy of the exosphere using LAMP and to D. Surface properties and processes are manifested in the planetary evolution as LADEE’s neutral mass and UV spectroscopic diversity of lunar crustal rocks. revealed by crustal measurements of dust using NMS and UVS. SCEM # 7. The Moon is a magnetism and space natural laboratory for regolith The third goal of the ARTEMIS investigation weathering. processes and weathering… deals with the structure of the lunar interior as Table 1. ARTEMIS science goals and their relevance to the determined by electromagnetic sounding from orbit. concepts and goals of the NRC report on the Scientific Context By studying differentiation of the lunar interior we for Exploration of the Moon can better understand the origin of all inner solar

system planets, including our own. Analysis of ARTEMIS Science Goals and Means. The first Apollo-era data indicates that the Moon formed by two goals of the ARTEMIS investigation deal with impact of a Mars-sized object with the early Earth, the lunar atmosphere, i.e., the tenuous lunar surface and later differentiated into primary crust, mantle boundary exosphere. Individual atoms rarely collide residuum, and possibly a small iron-rich core. The there (thus no chemistry is involved) and ions move Moon’s temperature and composition radial profiles, subject to the electromagnetic fields of the ambient as well as their lateral variability today hold environment. Ions and dust are constantly sputtered important clues regarding lunar differentiation history from the surface and then circulate in the exosphere and by inference that of Earth and inner system until they either escape into the solar wind or they are planets. Broadband (<<10mHz to 10Hz) trapped in permanently shadowed polar regions. electromagnetic sounding including novel use of the Interactions of sputtered and ionized particles, or magnetotelluric methods at higher frequencies will reflected solar wind ions, contribute to the dynamics improve knowledge of these state variables for the of the lunar wake. Similar atmospheres may surround core, mantle and crust. These are high priority goals Mercury, Europa, Ganymede and other bodies, but of the NRC report. the lunar atmosphere is the only surface boundary ARTEMIS is equipped with magnetic sensors of atmosphere accessible enough for detailed study in 3pT sensitivity and <100pT/12hr stability. The the next two decades. Therefore this goal is highly probes are on orbits that will bring them, one at a rated by the NRC report. Based on the availability of time, within ~100km from the surface or lower, i.e., the ARTEMIS orbits (i.e., an opportunity) and the at an altitude close enough to detect the core response health and status of the ARTEMIS instrumentation but least perturbed by crustal anomalies. Cross- (i.e., the technical readiness) this goal is rated even calibration during times prior to closest approach more highly in the list of ARTEMIS goals. enables offset removal. By comparing the periselene Recent Kaguya results have confirmed the signal from one probe to the driver signal from the presence of Na+ ions and also revealed the presence other probe further away we expect to achieve far of C+, O+, and K+. Ions with differing masses are greater sounding sensitivity than possible in the expected to be “picked up” by the solar wind and Apollo era: this is due to the stability of ARTEMIS attain the same (solar wind) average velocity, but can magnetometers, and the accurate removal of be distinguished further downstream by the geophysical plasma currents by use of concurrent ARTEMIS energy-angle ion spectrometers due to plasma measurements. their different energies. Kaguya has demonstrated excellent agreement between modeled particle motion in the presence of known electric and

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Furthermore, the highly sensitive electric field simultaneously explore the drivers and products of experiment on ARTEMIS provides a state-of-the-art exospheric source and loss processes, allowing us to measurement of the horizontal electric field at 1-10Hz, constrain the importance of each process and obtain which enables, for the first time, magnetotelluric information about the composition and structure of the investigations from orbit. ARTEMIS presents new lunar exosphere and its coupling to the surface. These capabilities for planetary investigations at the Moon, investigations are critical to the science questions on which can further constrain the radial profiles of surface-plasma interactions and will help us lunar composition and temperature, unraveling the understand surface-bounded exospheres encountered mystery of lunar formation and differentiation. on many other solar-system bodies (e.g., Mercury, Finally, ARTEMIS will study the interaction of asteroids, outer planet satellites). lunar crustal magnetic anomalies with the solar wind using its comprehensive particles and fields sensors. Initial Kaguya observations have already provided significant new information on an ion sheath, electron heating and solar wind reflection around magnetic anomalies at 100km (Saito et al., 2009), but waves properties and solar wind particle flow around the strong field region remain poorly understood. ARTEMIS will study the magnetic anomalies to infer properties of the ancient, seed magnetic field and to determine the accessibility of the solar wind to the surface and the effect it has on lunar surface ageing. Electric field and plasma wave data, together with ion and electron measurements in the vicinity of the mini- magnetosphere that forms around the crustal anomaly (the first comprehensive plasma measurements attempted at the Moon) promise exciting new science with possibly significant ramifications for planetary evolution. Relevance to NASA’s Solar System Exploration goals. Although ARTEMIS was primarily designed with several of NASA’s Heliophysics Division goals Figure 3.1 A schematic showing the trajectories of in mind, its unique instrumentation can address key recently picked-up ions and the expected Lunar science questions, important for Planetary measurements of the fluxes (top left) and composition Sciences. Many aspects of the Lunar environment (top right) of the picked-up ions. remain poorly understood, even though the Moon is our nearest neighbor. Notably, this includes the lunar Another highly rated science concept of the 2007 exosphere, which the recent NRC SCEM report NAS report concerns the: “processes involved with the prominently identified as a science priority. The atmosphere and dust environment of the Moon while species that populate the exosphere originate in the the environment remains in a pristine state”. As a solid solar wind, the surface, and subsurface, and are lost to body surrounded by a tenuous exosphere, the Moon’s the surface and to space by a variety of pathways. The surface lies directly exposed to the space environment, relative importance of the many exospheric source and including solar UV and X-rays, solar wind and loss processes is still under debate, and likely differs magnetospheric plasmas, and energetic particles. In an for each exospheric species. Both source and loss effort to maintain current equilibrium among these processes couple the exosphere to the surface, so that various populations of incident and secondary charged one cannot fully understand the exosphere without particles, the Moon acquires a dynamic electric field some knowledge of the surface. Similarly, many over its surface. As with most objects in space, to first source and loss processes are externally driven by order the lunar surface charges positive in sunlight and photons and solar and magnetospheric plasma, and negative in shadow, reaching potentials that vary over one cannot understand the exosphere and its coupling many orders of magnitude in response to changing to the surface without understanding the space solar illumination and plasma conditions. The environment around the Moon. ARTEMIS, with its full changing surface electric fields are suspected of plasma instrumentation, elliptical orbit spanning a transporting charged dust via electrostatic forces, thus large range of observational vantage points, and two- providing a possible link between solar/plasma point measurement capability, provides the means to conditions and dust dynamics observed in the lunar

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environment. The comprehensive field and plasma exosphere or at the surface. These measurements will instrumentation of ARTEMIS and simultaneous two- then be combined with the other, nearby ARTEMIS point measurements will help us understand the origin probe’s ESA and SST pristine solar wind data, and and dynamics of lunar electric fields. with GOES solar EUV measurements of the solar The 2003 NRC Decadal Survey noted that the activity to determine the relative variability of bulk compositions of the inner planets and the Moon exospheric source and losses and their dependence on remain poorly known, yet that knowledge is essential external drivers. in understanding the formation history of the inner planets and their satellites. For example, the models of the impact generation of the Moon by the collision of a Mars-sized object with the Earth would be further constrained if the bulk composition of the Moon were known more precisely. ARTEMIS studies of the deep Lunar interior from electromagnetic induction take advantage of the first simultaneous two-point magnetic field measurements of the nearby pristine solar wind and its effect on the Moon. This enables unique separation of the measured signal into a primary and an induction field. The technique is expected to provide new information on the structure, composition and temperature of the deep lunar mantle B-field

⊗ km) and lunar core. 3 V Z (10 3.1 Exosphere and plasma pick-up SW

Charged species discrimination: ARTEMIS will X (103 km) use charged particle measurements from the ESA and SST instruments as an extremely sensitive detector of the surface and exospheric properties, by measuring ions produced at the surface or in the exosphere and accelerated by solar wind electric fields. Newly created ions, produced by surface sputtering or ionization of exospheric gases are generated at Figure 3.2 (From Nishino et al., 2009) Ion and relatively low energies (0.01-10 eV), but immediately electron energy spectrograms from the downward- feel the effect of solar wind magnetic and electric looking SELENE (Kaguya) detectors. Kaguya (red- fields (which ARTEMIS will also determine). Ions are dashed circle in middle panel), is on a polar, 50-100 then accelerated in cycloidal trajectories (i.e. “picked km lunar orbit. It observed reflected solar wind ions at up”) as shown in Figure 3.1. the dayside, some of which can make it to the nightside Pickup ions are unique since their orbits have a equator, i.e., deep within the wake. Computer well defined energy and direction as a function of simulations reproduce the observations. gyrophase. Therefore, the pickup ions of a given species and flux detected at ARTEMIS at a given Recent Kaguya findings have advanced location near the Moon will be well-collimated and significantly our understanding of the solar wind nearly mono-energetic (beam-like). By measuring the interaction with the lunar surface as well as the near- pickup ion beams’ energy and direction and using EFI, Moon wake. Solar wind ions are reflected off the lunar ESA, and FGM measurements to determine the solar surface and from crustal magnetic field regions and are wind magnetic field and convection electric field, we then accelerated by the solar wind electric field to can back-trace the pickup ion trajectories, allowing the speeds as high as 3 times that of the solar wind [Saito ARTEMIS team to accurately determine the source et al., 2008]. The picked up ions find access to not region and differentiate between surface and only the high latitude wake, but also to areas deep exospheric sources [Hartle and Killen, 2006]. within the wake at low latitudes and altitudes, through In addition, ARTEMIS will roughly determine the fully kinetic processes (Figure 3.2). The solar wind ion mass, since both the ion energy and the size of the magnetic field and electric field can reconstruct the cycloidal trajectory scale with mass. ARTEMIS can observed proton spectra fully, assuming a reflected therefore use pickup ion measurements to remotely proton source on the dayside. probe the properties of neutral gases produced in the Yokota et al., 2009 used SELENE/Kaguya’s in situ mass spectrometry and confirmed the presence of

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Sodium in the Lunar exosphere. Sodium had Although ARTEMIS will generally be further previously been detected from the ground using a solar away from the Moon, the large geometric factor of the coronograph to occult the illuminated lunar surface ESA instruments and the long integration time (hours) (Figure 3.3). Kaguya’s observations from orbit have afforded by the 27hr-long, eccentric orbit will enable shown that the ions originate partly from the sensitive measurements of the pickup ions under stable exosphere and partly directly from the surface. Surface solar wind conditions. The technique will first be ions are able to obtain the full energy resulting from tested on lunar flybys in January through March of the electric field imposed by the solar wind; while 2010. When applied as function of lunar phase the exospheric ions, which commence their orbits midway technique will determine the dependence of the lunar between the surface and the detector, obtain less exosphere on lunar longitude undergoing illumination, energy. Thus energy can differentiate the source of thereby providing the ion composition versus those ions. The ions were observed by Kaguya at selenographic longitude. 100km altitude on the sunlit lunar hemisphere side that is favorably located for acceleration by the solar wind electric field. Moreover, Kaguya has shown that these dayside ions are composed of He+, C+, O+, and K+ in addition to Na+. Traces of Al+ were previously reported by WIND observations further from the Moon, and other species may also be present. The heavy ion flux varied with solar zenith angle but not with solar wind flux or meteor shower occurrences, suggesting a stable driver for the sputtering process. Within a distance of 2 gyroradii the ions can be discriminated in mass based on their energy and gyrophase by reconstructing their cyclical motion, shown in Figures 3.1 and 3.2, in external fields. Further away, a distinct, ion mass-dependent ring distribution in velocity space is expected.

Figure 3.3. Lunar exospheric Na, observed via remote sensing on a fortuitously clear night [Potter and Morgan, 1998]. Kaguya has recently measured the ionized Figure 3.4. [Yokota et al., 2009] Observations of Sodium. ARTEMIS sputtered ions from the lunar surface using the IMA will extend Kaguya’s sensor on Kaguya. The ions have sufficient flux to be results into the LRO and LADEE era and establish seen in the energy /charge spectrograms by IMA. their variability with solar activity. Feasibility. Many authors have demonstrated the The principle of operation and geometric factor of utility of pickup ion measurements in the way the ARTEMIS ESA instrument [McFadden et al., proposed by ARTEMIS to probe surface and 2008] are similar to those of the IEA (total ion) exospheric properties at the Moon [Cladis et al., 1994; instrument on Kaguya [Saito et al., 2008]. These total Yokota and Saito, 2005; Hartle and Thomas, 1974; ion instruments have a geometric factor 10 times Hartle and Killen, 2006; Hartle and Sittler, 2007]. larger than the IMA (ion mass analyzer) instrument on Though previous measurements of lunar pickup ions at Kaguya (Yokota). Figure 3.4 shows IMA instrument large distances from the Moon required very sensitive observations of accelerated ions from the lunar mass discrimination and background rejection [Cladis surface. ARTEMIS will provide information et al., 1994; Hilchenbach, 1993; Mall et al., 1998], concerning the continuous evolution of the energy fluxes of pickup ions near the Moon are both larger spectra as function of altitude from 100km to several and more collimated. Indeed, the geometric factor and thousand km. energy resolution of ARTEMIS suffice to measure these sources easily: For the three species in the lunar

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exosphere which are currently best understood (Ar, ARTEMIS will enable very accurate measurements of He, Na), convolving the exospheric neutral density upstream parameters and of local electric and with expected photoionization rates (both from Stern magnetic fields, allowing better back-tracing of ion [1999]) gives ion production rates of 10-3 - 10-2 cm-3 s- trajectories for appropriate orbital geometries. Since 1. Integrating ion production over a reasonable source ARTEMIS is in a similar part of the solar cycle, region leads to a prediction of pickup ion fluxes of results from the two missions can be compared and >103 - 104 cm-2s-1 near the Moon. This agrees with the cross-validated. more detailed particle tracing simulations of Yokota and Saito [2005], which predict pickup ion fluxes on the order of ~104 cm-2 s-1 for most major species near the Moon (see inset in the upper right corner of Figure 3.1) and Kaguya’s direct observations of such fluxes at 100km [Yokota et al., 2009]. Sputtered ion fluxes from the surface are similar [Cladis et al., 1994; Yokota and Saito, 2005]. For example, the upper left inset in Figure 3.1 shows the expected differential fluxes at ~100 km altitudes from Na sputtering and Figure 3.5 Kaguya measurements [Nishino et al, photoionization. The ions from the surface are nearly 2009] in the proton-governed region (PGR) indicate monoenergetic, while those from the atmosphere are that the wake electric field may be severely distorted still spread out in energy because the source is from its anticipated inward direction due to proton extended and the observation altitude is very low. At concentrations moving ballistically there, after their higher altitudes, the ions will be accelerated further, generation by solar wind scattering at the dayside. producing a much more monoenergetic spectrum and Measured ion and electron concentrations confirm much higher ion energies for both surface and that the nightside wake at 100km is quite dynamic. exospheric sources (with little reduction in flux unless Due to such plasma interactions the wake is expected significant scattering occurs in one ion gyroperiod). to host significant electric fields that likely map to the Using the two-point measurements and highly surface. elliptical ARTEMIS orbits, we can observe both exospheric and sputtered ions over a range of altitudes, ARTEMIS also complements LRO and LADEE, allowing us to determine their source properties quite being concurrent to both (also see Sections 3.6 and accurately. Due to their collimated and nearly 3.7). While LRO’s LAMP instrument will observe the monoenergetic nature the ion fluxes can be easily vertical scale heights of species such as Ar, H, OH and observed above background by either the ESA or SST H2 to understand volatile transport, ARTEMIS will instruments (depending on ion energy), especially measure the ionized fraction of those species, a result when the ions reach their peak energies near the apex of photo-ionization by solar UV radiation. LADEE’s of their cycloidal trajectory. Near the Moon, UV spectrometer (UVS) and Neutral Mass trajectories will be affected, to some degree, by: (1) Spectrometer (NMS) instruments will also observe magnetic perturbations due to crustal magnetic fields exospheric constituents both directly as neutrals, and [Halekas et al., 2001; Hood et al., 2001] (2) wake remotely via UV measurements. LRO and LADEE boundary currents [Halekas et al., 2005a], (3) electric thus measure gases before ionization, while perturbations due to lunar surface charging [Halekas et ARTEMIS measures them post-ionization. With the al., 2002, 2008] and (4) wake ambipolar electric fields solar UV flux known from other concurrent space- [Halekas et al., 2005b]. However, most of these borne instruments (e.g., GOES) it is possible to perturbations are small, and all of them can be correlate the ARTEMIS measurements with those on measured directly by ARTEMIS and/or determined LRO and LADEE and directly follow atmospheric from previous studies. Indeed, ARTEMIS’s ability to constituents from their source on the surface to their measure these perturbations is a key advantage in loss in the solar wind. By coordinating ARTEMIS understanding the details of pickup ion trajectories. measurements with those from LRO and LADEE the Synergistic Measurements – SELENE/Kaguya, community will greatly advance its understanding of which was in orbit around the Moon until a few the lunar exosphere, the exospheric coupling to the months ago, has an ion mass spectrometer. It could lunar surface and its escape rate into space. therefore detect pickup ions with better mass discrimination than ARTEMIS. However, the highly 3.2 Lunar Dust elliptical orbit of ARTEMIS enables high altitude The lunar surface electric field has been shown to pickup ion measurements that Kaguya could not make. respond closely to solar and magnetospheric plasma Furthermore, the unique two-point capability of and energetic particles [Halekas et al., 2007; Halekas

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et al., 2005b], and also to vary with inclination with determine all plasma currents incident on the surface, respect to the Sun. The largest lunar potentials occur thus facilitating accurate modeling of the charging on the nightside, in the absence of photoemission, process. where surface charging is primarily driven by ambient plasma currents [Manka, 1973; Stubbbs et al., 2007]. In turn, lunar electric fields affect the lunar ionosphere and exosphere, and may also control the distribution of charged lunar dust transported near the surface. Recent experimental results confirm the bulk properties expected of lunar electric fields, and have also yielded some surprises. Electron reflectometry techniques have been used on Lunar Prospector (LP) to measure the potential drop between LP and the surface [Halekas et al., 2002], and more recently to determine the absolute surface potential [Halekas et al., 2008, 2009]. On the dayside, surface potentials are small, and for much of the time below the sensitivity of the reflectometry technique. On the nightside LP data indicate potentials of −100 V or less in the wake and the magnetospheric tail lobes [Halekas et al., 2002]. A more startling result was the measurement of negative potentials occasionally as high as −4 kV in the tail plasma sheet [Halekas et al., 2005b] and during SEP events [Halekas et al., 2007, 2009]. More recently, Nishino et al., [2009] used the solar wind velocity measured on Kaguya to infer the motional solar wind electric field. In conjunction with the observed solar wind protons back-scattered from the sunlit side, this field provides a good prediction for ion signatures observed near the poles and the Figure 3.6 Measurements of the potential of the lunar equatorial wake (Figure 3.5). Contrary to the surface (Um), corrected for the LP spacecraft potential anticipated preponderance of electrons on the (Us/c) when the Moon is in the terrestrial nightside, there are occasions when positive ion fluxes magnetosphere, in sunlit and shadowed regions. accumulate, pulling the electrons in from the wake, ARTEMIS will enable the direct measurement of positive potentials in sunlight and establish which resulting in local electric field concentrations or particle populations dominate surface charging over a distortions of the inward electric field at the wake. broad range of solar and plasma conditions. The plasma and fields instrumentation on

ARTEMIS is far more comprehensive than that flown The ESA and SST combination on ARTEMIS will on previous missions, enabling significant strides also help determine the mechanism that causes high forward in our understanding of the origin and lunar electrostatic potentials during Solar Energetic dynamics of lunar electric fields: LP measurements Particle (SEP) events. These potentials likely result lacked direct knowledge of the spacecraft potential. from charging due to either energetic particles or Although the potential has been modeled on LP changes in the (lower energy) solar wind plasma (Figure 3.6), ARTEMIS will be capable of measuring distributions that may accompany some of these the spacecraft potential directly using its EFI events. By directly measuring particle fluxes over a instrument, and thus validate the model-dependent LP wide energy spectrum, ARTEMIS will directly results. The lack of an ion analyzer on LP made confirm or refute this hypothesis and identify the solar measurements of small positive dayside potentials wind particle population driving electrostatic charging. either extremely difficult or impossible. On Finally, ARTEMIS will explore the efficacy of ARTEMIS, the combination of electron and ion other surface electric field generation mechanisms, measurements will allow the extension of the which eluded detection by the low altitude orbit and reflectometry technique to consistently measure a wide incomplete instrumentation of LP. For example, large range of both positive and negative potentials, and to negative potentials are predicted within an “electron

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cloud” region in the wake expansion region [Farrell et could be readily detected from orbit [Farrell et al., al., 2008; Farrell et al., 2007]. Complete plasma 2007; Stubbs et al., 2006]. measurements on ARTEMIS from a range of altitudes ARTEMIS is expected to play a key role in in the sunlit regions of the wake expansion, just ongoing and future efforts to understand dust behind the terminator can reveal the predicted dynamics in the lunar environment. Maps of the lunar “electron cloud” and study its interaction with the surface potential obtained using the reflectometry surface. techniques described in the previous section will reveal average and extreme charging conditions that 3.3 Dust Transport contribute to dust dynamics. Dust transport is believed to occur on all airless Equally important is gaining an understanding of bodies in the solar system -- such as the asteroids the dominant currents involved in the charging [Colwell et al., 2005], Mercury [Ip, 1986] and many of process, enabling predictive capabilities to be put in the Moons of the outer planets -- and in some cases place for future missions. Currently, knowledge of the may be a significant process in determining the Moon’s location and average plasma properties of evolution of their surface regolith. The development of different regions (solar wind, magnetosphere, geotail) surface electric fields discussed in the previous section is not sufficient information to predict lunar surface may transport charged dust via electrostatic forces, charge. The LP results underscore the need for thus providing a possible link between solar/plasma continual monitoring of the plasma conditions and conditions and dust dynamics in the lunar electric fields around the Moon, which can be highly environment. These processes may be responsible for variable due to episodic SEP events combined with the presence of dust at high altitudes; for example, passages through the dynamic magnetotail plasmas. observations by Apollo astronauts from orbit of a ARTEMIS’ complete characterization of ion and “lunar horizon glow” (LHG) above the terminator is electron plasma currents incident on the surface over a thought to be due to the scattering of sunlight by an broad energy range will reveal the missing cause-and- electrified exospheric dust population extending to effect relationship of plasma conditions to surface altitudes in excess of 100 km [Zook and McCoy, potentials in these varied plasma environments, 1991]. McCoy [1976] used coronal photography from including the episodic extremes. In addition, the role Apollo to estimate dust concentrations ranging from of the wake in surface charging and subsequent dust ~105/m3 near the surface to ~10 /m3 at 100 km. trajectories is, at present, only speculative. The It is generally accepted that ambient solar and ARTEMIS wake investigations, aiming to characterize plasma conditions play a central role in dust motion on the electric field structure and loss of neutrality in the airless bodies, via electrostatic levitation of charged low-altitude wake expansion region will determine grains. This is known to occur at low altitudes on the how these processes are linked to the lunar surface Moon: images obtained by the Surveyor landers [Farrell et al., 2007]. showed a glow along the western horizon after sunset [e.g. Rennilson and Criswell, 1974]. The phenomenon 3.4 Interior Structure and composition of the Moon of dust levitation in a plasma sheath has also been from Electromagnetic induction reproduced in the laboratory [Sickafoose et al., 2002]. Determining the interior structure of the Moon The Apollo 17 Lunar Ejecta and Meteorite (LEAM) provides a key constraint on the history and evolution experiment may have yielded direct evidence for the of the Moon. Electromagnetic (EM) subsurface electrostatic transport of lunar dust. LEAM was sounding using natural energy is one of the oldest designed to detect hyper-velocity meteoritic impacts branches of geophysics, which can be used for lunar and associated ejecta (> 10 km/s); however, it instead sounding. EM sounding techniques seek to determine detected highly-charged dust grains of lunar origin the conductivity structures of solid-body interiors, moving at < 1 km/s with impact rates up to 100 times which is often sufficient to provide major insights greater than anticipated [Berg et al., 1976; Colwell et regarding the interior (e.g., radius of lunar core or al., 2007]. This activity peaked at the terminators, existence of Galilean satellite internal oceans). Further which strongly suggests that it is associated with the knowledge is gained in turn by using laboratory LHG. More recently, a dust fountain model has measurements of conductivity [Duba et al., 1974; described how charged lunar dust can become Constable et al., 1992; Xu et al., 1998; Yoshino et al., electrostatically “lofted” to high altitudes when the 2006] to constrain allowable mineralogy and forces due to surface charging effects are able to temperature. overcome gravity and cohesion. The charged dust is EM sounding exploits the fact that eddy currents then rapidly accelerated through the plasma sheath and are generated when a conductor is exposed to a subsequently follows a ballistic trajectory where it changing external magnetic field. The eddy currents generate their own magnetic field called the induction

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field, which is readily measured by ground or space the Moon from one lobe to the other twice per day, the instruments (see Figure 3.7). The depth to which a Moon will see very low frequency (50μHz to 50mHz) signal can penetrate depends on its frequency and the external drivers, ideal for probing at great depths. In conductivity of the probed material. By using multiple the magnetotail, traveling compression regions and frequencies, electromagnetic sounding has been used interplanetary shocks, have well characterized electric successfully to probe the upper mantle of the Earth and magnetic signals, and provide also high fidelity, [see Parkinson, 1983; and references therein] and the high frequency drivers (0.05-10 Hz) well suited deep lunar mantle, placing limits on the size of the magnetotelluric investigations. lunar core [Dyal et al., 1974; Russell et al., 1981; Hood et al., 1982] to be ~ 500 km in radius. More recently EM induction was used to discover liquid water oceans in the icy Galilean satellites of Jupiter [Khurana et al., 1998; Kivelson et al., 1999, Kivelson et al., 2002]. Two independent pieces of information are needed to derive the EM impedance at each frequency (see Grimm and Delory, 2009, for a review). The principal approach during the Apollo project was to use the magnetic transfer function between a distant satellite (source field) and a surface magnetometer (sum of source and induced fields). In special cases where the source field is known, a single magnetometer can be used (though having accurate measurements of the driver field is certainly preferable). The motion of the Galilean satellites in Jupiter’s main field (Khurana) and the near-uniform field in the earth’s geomagnetic tail (Russell et al., 1981, Hood et al., 1999) are two examples of the latter. The only other way that the impedance can be determined from a single platform is by correlation of orthogonal electric and magnetic fields, i.e., the magnetotelluric (MT) method (see Vozoff, 1991, for a review). As a single-platform measurement, MT is also not subject to spatial aliasing that may hamper transfer functions at high frequencies, and hence MT is optimal for relatively shallow probing of the outermost parts of the moon. ARTEMIS will use both Figure 3.7 Top: Principle of planetary scale methods—transfer function, and MT—to sound the electromagnetic induction. A time-varying primary lunar interior. Both methods rely on ambient field (red) induces a multipole secondary field (green geophysical signals to sound the interior. lines; only dipole response shown) that is directly Driver signals. A broad spectrum of frequencies is related to the electrical properties of the interior. available for lunar EM sounding as the Moon orbits Bottom: In practice, dayside response is confined about Earth. The largest fraction of the lunar month is when the moon is in the solar wind. Both this spent in the solar wind and the magnetosheath, where geometry (Sonett et al., 1972) and the near-vacuum turbulent waves, shocks and other structures can be nightside and magnetotail responses (Dyal et al., used for sounding. The supersonic solar wind results 1974) were exploited for whole-moon soundings. The in confining the Moon’s inductive signal near the magnetic-transfer approach between a distant satellite surface on the dayside. However, in the near-vacuum (Explorer 35) and the Apollo 12 Lunar Surface cavity on the dark side, the magnetic induction signal Magnetometer (LSM) is also illustrated; Artemis will propagates far away and can be sensed from orbit. use this technique between near and distant probes Additionally, for ~4 days each month, the Moon with higher fidelity magnetic data accompanied by passes into the Earth’s geomagnetic tail, consisting of excellent characterization of the plasma environment two near-vacuum magnetic lobes, sandwiching a dense from plasma data. Additionally, ARTEMIS will test the sheet of plasma moving at subsonic speeds. There the magnetotelluric method, which relies on correlations lunar induced response in tha tail is symmetric on the between electric and magnetic fields at a single probe. dayside and the nightside. As the Earth’s dipole brings

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EM transfer function sounding. Using the transfer function method, Apollo and Lunar Prospector (LP) data has constrained the radius of a highly conducting lunar core to < 400 km (e.g., Hood et al., 1999) and determined the deep mantle conductivity (e.g., Hood et al., 1982, Hood and Sonett [1982]) and its relation to the geothermal gradient and thermal evolution of the Moon. However the transfer function is not very well constrained at depths less than 500km from the surface or radial distances less than 500km from the center (Figure 3.8) because at high frequencies the planar approximation breaks down and at low frequencies there are uncertainties in distinguishing the induction signal due to instrument offsets or noise. For example, Explorer 35 data, used to determine the driver in the Apollo era, had significant offset fluctuations; while the lack of simultaneous plasma measurements prohibited identification and removal of ambient, space currents. Lunar Prospector studies did not have a nearby monitor of the driver signal. Hood (1984) and more recently Grimm and Delory (2008) argued that previous datasets are still inadequate for constraining the conductivity profile at all distances, and that the lunar core remains compatible with either metallic or silicate composition. Grimm and McSween (2009) recently calculated that tens of ppm H2O (Saal et al., 2008) can best explain the deep mantle conductivity, in lieu of high-alumina pyroxene. ARTEMIS will measure the external, driving magnetic field with one spacecraft and the response of the lunar interior to that field with probe near the surface. Differencing the highly sensitive magnetometer signals on the two spacecraft under various external driver frequencies is an ideal way to sound the interior conductivity of the Moon as function of frequency. For the first time the technique will be applied using nearby spacecraft, bearing identical sensors with very stable offsets, that can be cross-calibrated just hours prior to each pass, and can benefit from on board plasma measurements to remove localized space currents. The ARTEMIS periselene altitude will be approximately 100km (exact altitude depends on results of orbit stability analysis optimizing for planetary goals). This altitude is ideal for making induction measurements from orbit, because with the exception of known, localized magnetic anomalies all Figure 3.8 Top: Apollo-era electromagnetic sounding other variances from the input signal can be attributed of the lunar interior: Electrical conductivity versus to induction effects. The technique can be applied both radial distance from Moon’s center (km) inferred from in the solar wind at the nightside and in the various sources, including Hood et al., 1982. Dashed tail/magnetosheath/lobes on either side of the line corresponds to anhydrous basalt. Middle: terminator. Temperature-depth profile inferred by Hood and Sonett [1982] using laboratory data, assuming conductivity is dominated by high-alumina pyroxene. Bottom: Laboratory measurements of mineral conductivity vs. temperature.

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Magnetotellurics. EM sounding using the transfer lunar interior accurately over a broad frequency range. function method is valid at low frequencies (<10 mHz) On board plasma instrumentation allows diagnosis of where wavelengths are large relative to the lunar the ambient environment and culling of intervals radius, and the lunar response is well represented by a affected by ambient plasma effects (e.g., tail current dipole. In that case, assumptions regarding spherical sheet crossings, sputtered ions at the nightside, symmetry of the conductivity apply. Beyond 10mHz neutralizing electron currents). and up to 40mHz it is possible to extend the theory An important benefit of magnetotelluric sounding using a multipole approximation [Sonett, 1982; Sonett is that at shallow depths conductivity profiles are et al., 1972] though this requires assumptions on the local. Given the near-equatorial orbits of ARTEMIS wave-front propagation direction and speed. However, probes, this enables determination of the lateral above 40mHz it is no longer possible to use heterogeneity of conductivity, i.e., primarily as magnetometer data alone, because phase velocities and function of selenographic longitude. Such information speeds are only local and uncorrelated with the far could take the field beyond the spherically symmetric away driver signal monitor. In that case a complete lunar magma ocean hypothesis formulated in the electromagnetic sounding can only be performed with 1970’s thanks to Apollo era data. Evidence for such the magnetotelluric method: The ratio of orthogonal heterogeneity in the lunar differentiation process has magnetic and electric signals at a single point results been found in the Lunar Prospector measurements in the apparent conductivity as function of frequency; (Figure 3.9), and it is quite possible that ARTEMIS this can be inverted to a conductivity-depth profile may characterize further this heterogeneity in the lunar (Vozoff, 1991; Simpson and Bahr, 2005). magnetotelluric response. In summary, ARTEMIS will perform EM lunar transfer sounding measurements of unprecedented quality. Using state-of-the-art instrumentation and extremely high knowledge of the driver field, it will establish improved bounds on the deep subsurface conductivity profile, and has the potential of distinguishing between the silicate versus ferrous core hypotheses. ARTEMIS’ comprehensive fields and particles instrumentation, data collection capability and mission design allow us to utilize for the first time Figure 3.9 The asymmetric distribution of Thorium the technique of magnetotellurics from lunar orbit, to and (by inference) of other incompatible elements determine the subsurface conductivity at shallower (Potassium “K”, Rare Earth Elements “REE”, and depths than previously possible. Correlating that Phosphorus “P”, otherwise known as KREEP) information with known features in surface bespeak of heterogeneity in the formation of the lunar composition and age can result in a more thorough crust that cannot be explained currently. understanding of the asymmetric mantle development during lunar differentiation. Although routinely used at Earth, magnetotelluric sounding has never been attempted at the Moon, 3.5 Surface properties and planetary evolution as because never before have there been electric field revealed by crustal magnetism and space instruments flown in the lunar environment. The weathering. method is most valuable at higher frequencies (1- Crustal magnetism preserves ancient records of 10Hz), which are least affected by spatial aliasing of planetary and surface evolution. At Earth, study of an orbiting satellite. ARTEMIS coIs Delory, Halekas crustal fields revealed polarity reversals of the core and Grimm have been independently funded by NASA dynamo and established a chronology that ultimately to analyze existing datasets and determine confirmed the plate tectonics hypothesis. The origin of detectability limits of conductivity at various depths lunar magnetism is less clear because of the absence of from ground or space platforms. Preliminary analysis a present day dynamo (the lunar dynamo is at least 8 indicates that a geophysical signal ~0.1mV/m/sqrt(Hz) orders of magnitude less than that of Earth’s if it exists at 1-10Hz is expected from an orbital platform at all [Russell et al., 1978]). Lunar sample (e.g.,ILN SDT, 2009, p. 38); this signal is ~5 times the measurements indicate the possible presence of a lunar sensitivity limit of ARTEMIS’ EFI instrument from its dynamo from 3.6-3.9 Ga (Cisowski et al., 1983) with 40m and 50m tip-to-tip radial sensor pairs (Bonnell et an order of magnitude decrease before and after that al, 2008)). ARTEMIS periapsis measurements lasting period. Like at Earth, thermoremanent magnetization for 10s of minutes, at a cadence of 128Hz will be is expected to have magnetized igneous lunar samples captured in burst mode and will enable sounding of the during that period. However, lunar magnetic fields are

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stronger over highlands than over maria, in agreement A mini-magnetospheric interaction should result in with the absence of a recent strong lunar dynamo to solar wind density enhancements at the front and at the magnetize recent lava flows (Coleman et al., 1972). edges of the anomaly, but density depletions in the Lin (1988) showed that the largest concentration of center (where solar wind ions are excluded). Indeed, crustal fields is diametrically opposed to the Imbrium, shock-like features consisting of plasma density and Serenitatis, Crisium and Orientale impact basins magnetic field increases are often observed by LP over (Figure 3.10) as confirmed by Lunar Prospector and crustal magnetic anomalies in the solar wind; however, modeled empirically (Mitchell et al., 2008). Shock the expected density decrease is seldom observed in remanent magnetization may have magnetized the the electrons, even at very low altitudes [Halekas et metamorphosed breccias in these impact basin al., 2008]. We note that the LP mission did not have a antipodes, and possibly also in basin ejecta terranes. solar wind or ion spectrogram monitor. On the other hand, the ion spectrometers on SELENE/Kaguya did observe deceleration and reflection of ions from crustal magnetic anomalies [Saito et al., 2009]. The two strongest anomalies on the near side, Reiner Gamma and Descartes, and the strongest one on the far side, Crisium antipode, have surface fields that likely exceed 1000nT [Hood and Williams, 1989; Richmond et al., 2003] and all three anomalies provide typical examples of the general correlation between crustal magnetic field regions and high albedo “swirl” features [Hood et al., 1979; Hood and Schubert, 1980; Figure 3.10 Impact basin rims (white circles, for Richmond et al., 2003, Nicholas et al., 2006] (see Imbrium interior ring also shown) and their antipodes Figure 3.12). Reiner Gamma modeling results in (black circles), superimposed on a map of total magnetizations of 1-10A/m for layers of 1000 – 100 m surface field intensity averaged on 5x5deg bins respectively, with the source being very close to the (Mitchell et al., 2008). surface. This suggests the magnetized layer was due to ejecta from nearby Imbrium impact, and material that Highland breccias carry the strongest permanent was subject to ageing. Similar analysis at Descartes magnetization of all lunar samples today (Fuller and shows that the magnetization there is also likely Cisowski, 1987). These rocks are more efficiently concentrated in ejecta from nearby Imbrium or magnetized because they contain more metallic iron Nectaris. grains (likely produced by meteoritic impacts). Mare The correlation between regions with high albedo basalts, on the other hand, contain less nanophase iron and crustal magnetization may imply that strong and generally have weaker remanent magnetization. surface magnetic fields could be responsible for Shock remanent magnetization requires the prohibiting the optical maturation of the regolith, combination of an impact-generated shock and the otherwise known as “space weathering”. On the presence of a magnetizing field, either from the lunar Moon, spectral darkening was originally believed to core or from the solar wind of 3.6-3.9 Ga ago. The be caused by the accumulation of agglutinates, glass- magnetization may be enhanced in the antipodal rich aggregates formed by melting as a result of regions by compression of the magnetic field by an micrometeorite impacts (Adams & McCord, 1971a,b). ionized plume originating at the impact site (Figure These complex structures were known to contain a 3.11). reduced form of iron (nanophase Fe – npFe0), Whatever the origin of these magnetic anomalies, generated by impact melting of solar wind hydrogen- they are expected to stand off the solar wind or the enriched regolith. However, recent work has identified magnetosheath plasma, possibly forming a mini- npFe0 itself and not the agglutinate particles as the magnetosphere, i.e., a density cavity [Omidi et al., darkening agent, which also explains the spectral 2002; Harnett and Winglee, 2003]. Lunar Prospector reddening seen on the Moon and more importantly on has observed features suggestive of such an other weathered bodies (Hapke, 2001; Pieters et al., interaction, including shock-like signatures in the 2000). Moreover, the npFe0 is now believed to be electron and magnetic field data [Lin et al., 1998; formed by a fractionation process from solar wind Kurata et al., 2005; Halekas et al., 2008]. In addition, sputtering, vapor released by energetic micrometeorite recent observations from SELENE/Kaguya have impacts, or both (Pieters et al., 2000). identified the anomalies both in the magnetic field data at 100km [Tsunakawa et al., 2008] and, more readily, in the plasma data [Saito et al., 2009].

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form mini-magnetospheres. Despite this ongoing research, there is as yet no consensus on the relative importance of fluid or kinetic effects in these features, or whether they form shocks or whistler wakes such as suggested by Omidi et al (2002). While LP results are suggestive, other workers have stopped short of characterizing these features as mini magnetospheres (Lin et al., 1998) ARTEMIS, together with recent Kaguya data, possesses the complete set of plasma instrumentation necessary to help resolve this question. If RG is found to form an effective shield against the solar wind, this would imply that solar wind ion sputtering is an important or perhaps even dominant process for space weathering when compared with the micrometeorite contribution alone. These results can then be applied to other swirl features in order to explore the pervuasiveness and importance of this process over the lunar surface, and by extension other airless bodies throughout the solar system.

Figure 3.11 Adapted from Hood and Artemieva [1987]. A possible antipodal magnetization mechanism takes advantage of a global field from an early lunar dynamo (top, A and B) or an enhanced solar wind field (bottom A’ and B’). The transport of partially ionized impact ejecta from the impact site excludes this initial magnetic field, resulting in a field concentration at the impact antipode an hour to a few hours later. If this field compression is contemporaneous with enhanced shock pressures from antipodally focused impact ejecta and/or seismic energy, strong shock remanent magnetization can be impressed into both the local material and the Figure 3.12 Left: Descartes mountains albedo and its transported debris from the impact site. The depth, correlation with magnetic field magnitude at 19km, intensity and orientation of the crustal field holds, near the Apollo 16 landing site, shown in a box at the therefore, key information regarding the seed center (from Richmond et al., 2003). Right: Reiner magnetic field 3.6-3.9 Ga, at the time of formation of Gamma albedo (top) and its correlation with the these magnetic anomalies. Northerly magnetization (bottom) shown as contours at 0.1 A/m atop a 40km thick magnetized layer (from Reiner Gamma is an ideal feature to study in the Nicholas et al., 2006). context of space weathering, and has the potential to reveal the importance of the two competing Although recent impacts that bring up fresh weathering processes on the Moon: micrometeorites or material are also accompanied by high albedo, it is the solar wind. There is a close correlation between the possible to use albedo information and the knowledge albedo morphology and the anomalous magnetic field, gained from observations of intense anomalies including dark and light bands that may indicate open observed on orbit to understand other anomalies with and closed field line topologies. LP results also imply higher order poles that may not extend as far into the that the Reiner Gamma anomaly may indeed solar wind, yet are still able to fend the solar wind off effectively shield the surface from the solar wind at lower altitudes. This can provide further (Kurata et al 2005), and thus be classified as a “mini- information about surface magnetic topologies that magnetosphere.” Simple fluid MHD models (Hood & cannot be accessed by magnetic field measurements Schubert, 1980) and 2-D fluid simulations with from high orbit or remotely sensed using electron multipole field structures (Harnett & Winglee) reflectometry. indicate that RG and other small-scale anomalies can

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In fact, the Kaguya plasma team has recently The LAMP EUV spectrometer’s observations of the reported observations of solar wind ions reflected from lunar atmosphere and its variability are key LRO magnetic anomalies, with the typical surface objectives during the main mission. In the extended backscattering observed over the unmagnetized mission these objectives expand into the study of the surface absent in the vicinity of such anomalies. structure and variability of the exosphere, the horizon Electron heating due to turbulent electric fields is glow and the search for active outgassing regions. expected and observed at the interface of solar wind LAMP will probe the vertical scale heights of and the magnetic anomaly [Saito et al., 2009]. That constituent species, such as Ar, H, OH and H2 to interface is expected to be a host of numerous plasma understand volatile transport processes with dedicated instabilities and electron populations that can remotely campaigns. Understanding the path of those species sense the entire field line. These observations suggest requires correlating their occurrence patterns and that significant knowledge regarding the properties of characteristics with external drivers such as the solar the lunar crustal anomalies can be obtained from orbit, wind and magnetotail plasma fluxes and field by the study of the crustal field’s interaction with the orientations, parameters readily provided by ambient plasma. Specifically, the extent of influence ARTEMIS. of these interactions into the environment (solar wind, ARTEMIS can support LAMP observations of the magnetosheath or magnetotail) can provide exosphere by providing accurate measurements of information on the strength, multipole order, depth and solar wind and magnetotail drivers. For example, if the orientation of the underlying dipole. This information, Moon has a Lyman alpha corona, it is possible that it in turn, is related to the conditions at the time of varies with solar wind electron flux or external electric magnetization and can be used to constrain the initial field intensity/magnetic field topology. Topographic driver field. For example, random polarities at nearby measurements of source regions with LAMP can also sites would favor a solar wind seed, whereas polarities be directly compared with charged particle surface organized at a great circle, or meridian, could favor an sources from the ARTEMIS’ investigation, reinforcing internal dynamo theory. the findings or providing salient differences between ARTEMIS will measure lunar fields from 100km or the two techniques. Comparisons of ARTEMIS’s in- less, depending on the periapsis and longitudes that situ charged species loss rate measurements and will be attained, at a 10° inclination or greater (goal ~ exospheric source determination, when compared with 20°), depending on the communications link budget LAMP’s observations of these species’ neutral source and fuel margin available. It will study the interaction populations from the same epoch provides a very of near-equatorial magnetic anomalies with the solar strong synergy relating the exospheric constituent wind and the magnetotail. Near equatorial anomalies losses directly with their source population. which have been observed already by Observations during the overlap period between SELENE/Kaguya at 100km altitude include Reiner LADEE and ARTEMIS can be used as calibration Gamma (8N, 58W), Rima Sirsalis (12 S, 58W), points to relate the statistical studies that will be done Descartes (11S, 16E) and Crisium antipode (20S, independently by the two missions. 124W). The equatorward portion of South Pole – CRaTER’s objective to study Galactic Cosmic Aitken (20-50S, 150-180E) may also be measured. Ray (GCR) and Solar Energetic Particle (SEP) These anomalies deflect and shock the solar wind populations to constrain radiation transport models plasma and cause electron heating and wave and determine the temporal variation of radiation turbulence. Even from 100km altitude and from effects at the Moon is particularly well facilitated by inclination below 10°, the comprehensive the presence of ARTEMIS as a nearby solar wind instrumentation on ARTEMIS will measure the monitor. Variations in GSRs and SEPs at lunar magnetic properties of Reiner Gamma and the distance depend on the location of the Moon relative interaction of this mini-magnetosphere with the Solar to the magnetosphere and solar wind, the Wind and the Earth’s magnetotail. interplanetary magnetic field orientation and connection to the Sun, and variations in flux of solar 3.6 ARTEMIS and LRO wind plasma. This is particularly true for SEPs with Because it overlaps with LRO’s extended ~100 keV energies, whose flux can vary by orders of investigation in FY11 and FY12, the ARTEMIS magnitude as the Moon moves through the mission is in a unique position to support LRO’s prime magnetotail plasma sheet and lobes, the and extended mission science objectives. LRO will magnetosheath or the solar wind. As these study the lunar atmosphere and its variability with the magnetospheric regions are very dynamic, only a lunar LAMP instrument, and particle acceleration solar wind monitor can determine them accurately and mechanisms and their radiation effects on tissue with provide the necessary input to model and interpret the the CRaTER instrument. CRaTER measurements.

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ARTEMIS mission during its low-altitude phase (~100 3.7 ARTEMIS and LADEE km) about the Moon. The synergy is immune to a By measuring both upstream solar wind and local launch delay because the ARTEMIS probes will be in plasma conditions near the Moon, ARTEMIS is in a stable orbits for many years. The LADEE deputy unique position to support the Lunar Atmosphere and project scientist, Dr. G. Delory, is also an ARTEMIS Dust Environment Explorer (LADEE) mission, slated co-I, ensuring early and effective scientific and for a mid-2012 launch. LADEE carries operational coordination between these two missions instrumentation to study the dynamics of the lunar prior to their lunar conjunctions. exosphere and dust environment, much of which will be tied directly to the ambient plasma conditions at the 3.8 ARTEMIS and International Lunar Network. Moon and in the solar wind. Sputtering by the solar A major element of NASA’s lunar flight projects is wind has been proposed as a possible mechanism for the International Lunar Network (ILN), comprised of the generation of neutral exospheric species such as small geophysical nodes on the lunar surface. These Na [Potter & Morgan, 1994], along with photon- nodes are expected to be deployed in the next decade stimulated desorption (PSD) and micrometeorite by NASA and international space agencies, with the impacts [Mendillo et al., 1999]. Although recent goal to improve our understanding of the interior Kaguya results suggest that the solar zenith angle is structure and composition of the moon (ILN SDT, the dominant effect on the observed Na+ flux, distinct 2009). One of the goals of the ILN is to perform lunar changes in the exosphere have been observed when the EM sounding from the surface with both electric and Moon enters the magnetotail [Potter et al., 2000; magnetic sensors. Magnetotelluric measurements are Wilson et al., 2006], indicating the importance of the baseline ILN measurements to achieve a desired goal local plasma environment on exosphere dynamics. of the ILN, however magnetometers alone could Most recently, correlations between Lunar Prospector provide an ILN measurement floor, assuming a low- plasma data and ground-based observations indicate orbiting magnetometer was available. ARTEMIS can that ion impact may enhance PSD efficiency [Sarantos provide continuous magnetometer measurements of et al., 2008], possibly due to the introduction of the driver signal to meet the needs of the measurement crystalline lattice defects in the regolith. This recent floor of the ILN network EM sounding goal. discovery is a preview of the synergies possible ARTEMIS’ magnetotelluric observations from orbit, between ARTEMIS and LADEE, in which one over various spatial and temporal locations also spacecraft measures the complete plasma inputs to the complement the magnetotelluric measurements of the system, while a second monitors the exospheric expanding ILN network of nodes during the next response. Since LADEE lacks any plasma decade. instrumentation, the presence of ARTEMIS will enable a more direct linkage to be made between the 4. Planetary Science Trade Studies specific plasma processes and the resultant exospheric variability measured by LADEE. Similarly, The ARTEMIS team is committed to optimize the ARTEMIS plasma measurements will cast light on the science return for the Planetary investigation of the processes causing any dust activity measured by mission without affecting its Heliophysics LADEE. To first order, LADEE measurements will commitments and without posing risk to the probes or confirm or refute some of the more obvious potential undue burden on operations. The following are the sources of lofted dust, such as the photoemission- trade studies that will occur in 2010-2011; the results related day-night asymmetry at the terminator region will be documented in a special issue of Space Science where the surface potential of the Moon is known to Reviews on ARTEMIS. change on a regular basis [Farrell et al., 2008; Halekas et al., 2005b; Manka, 1973; Stubbs et al., 2006]. It is 4.1 Periselene reduction also possible that dust activity is rare on the Moon, The ARTEMIS orbits are affected most by Earth occurring only during extreme charging events perturbations, and less by lunar perturbations because [Halekas et al., 2007, 2009] or follows unexpected most of their time is spend far from the Moon. Orbits temporal or spatial patterns. In this case ARTEMIS are rather predictable with the periapsis altitude measurements of the plasma conditions and surface exhibiting periodic behavior dominated by an potential could revolutionize our understanding of the oscillation at 1/2 the lunar orbital period with a underlying physical mechanisms at work which would secondary oscillation at four times the lunar month have otherwise gone unnoticed with LADEE (Figure 4.1). Both modes of the periselene oscillation measurements alone. can be reduced by lowering aposelene, and the orbit The LADEE launch is currently planned for mid- can be further optimized to “graze” the surface in the 2012, and thus will overlap with the nominal <100km domain once a month. By expending

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maintenance fuel on the order of a few m/s it is possible to maintain a stable orbit at low periselene. The operational aspects of this optimal design will figure prominently in this trade study, including: position knowledge accuracy from Doppler tracking data obtained between trajectory correction maneuvers; fidelity of long-term orbit predicts from models; and burn targeting accuracy.

4.2 Inclination adjustments An inclined orbit increases the gravity gradient torque on the spin axis away from its optimal orientation of 3-13° (8° nominal). This affects communications as there are significant signal losses below 15° from the spin plane. Spin axis station- keeping results in a 225 gr/year fuel expense assuming a 26° inclination, which is equivalent to 5m/s/year and should be gauged against ~5 m/s/year needed for periselene station keeping. Further inclination increases or fuel reductions are also possible assuming data can be lost from a small part of the orbit whose location depends on the time of year and the evolution of the inclination/spin axis as function of mission elapsed time. The trade space includes thermal considerations (top deck illumination runs the spacecraft hotter), boom shadow effects (for solar incidence angles greater than 10° the magnetometer booms shadow the solar array resulting in spin tones in the magnetometer measurements during one portion of the year). The study will culminate in a Figure 4.1 Current periapsis altitude of ARTEMIS recommendation for an inclination/spin axis attitude probe P1 and P2, optimized only for heliophysics that will optimize science at low additional operational studies. For purposes of Planetary science, a <10m/s costs for the amount of fuel available. burn (margin is available, see Section 7) or further optimization of the orbit insertion maneuvers can 4.3 Instrument Planetary rates and modes result in lower periapsis (<100km). Lowering of The five instruments on each ARTEMIS probe can apoapsis can further reduce the periapsis spread from be run in ways that optimize planetary objectives Earth perturbations. Such orbits are expected to result without reducing their efficacy for heliophysics in ~ a dozen “grazing” lunar encounters per probe science. We will consider the following: (i) Averaging per year, or about three dozen low altitude passes in particle distributions rather than capturing snapshots, the period 2011-2012, and continue with minimal to increase counting statistics at no volume expense. maintenance thereafter. This is needed for high quality measurements of exospheric species. The cadence and orbit duration of 5. Instrument Operations for Planetary these measurements will depend on volume allocation. (ii) Time-based perigee burst mode collection for The ARTEMIS science team together with the magnetotelluric and crustal fields/space weathering instrument engineers and instrument leads will science. The burst duration, cadence and products will consider the following operational changes to the have to be adjusted to values optimal for capturing this instruments for the purposes of the Planetary science based on orbit characteristics (duration below investigation. The changes will not affect the team’s maximum useful altitude). (iii) Apportionment to slow commitments to Heliophysics science. These changes versus fast survey modes, and data products returned will be documented in a special issue of Space Science will have to be revisited to optimize exospheric Reviews on ARTEMIS. science versus low altitude science. At nominal rates 5.1 Particle instrument mode changes and products, it is expected that 3.5 hrs of fast survey, The ESA instrument (McFadden et al., 2008) 22.5hrs or slow survey and 2 particle bursts (with 2 operates in the magnetosphere by scanning in energy wave bursts each) will not saturate the memory. from 3eV to 25keV, on 32 energy channels and 88

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angles. At stored maximum resolution of 22.5 o, these 30keV – 6MeV for ions and 30keV – 1MeV for 88 angles cannot fully resolve the solar wind beam and electrons. Its lowest energies are well-suited to pickup thus the instrument was designed to have a special ion detection. Increased energy resolution at these “solar wind” mode that increases angle resolution to lower energies will enable the better mass 5.125o producing accurate solar wind plasma moments differentiation needed for planetary objectives. The but reduces the energy resolution to only 50eV-5keV. corresponding decrease in energy resolution at higher These two separate modes suffice for doing energies represents a minor sacrifice for heliophysics heliophysics science at the Moon when in the studies of ion acceleration to high energies. magnetosphere or the solar wind, and switching between them is accomplished using time-based commands on orbit predicts with standard magnetospheric models. Planetary science, however, requires capturing both the solar wind input to the lunar environment and the spectroscopic differentiation of species, many of which are expected to occur at higher energies due to their greater masses (e.g., pickup Na+ ions will be seen as a ring in velocity space from 0 km/s to 2VSW, or ~800km/s, which corresponds to 4keV*(mNa+/mH+)=92keV. While the species can be differentiated based on their lower energy signatures, this calculation suggests that the method requires energy detection up to (and beyond) the maximum energy of the ESA detector (30keV) and into energy range of the SST instrument. Figure 5.1 The power currents create a ripple visible The plan is therefore to develop a special mode for the in the magnetometer signal at quiet times. This can be ESA, which preserves energy range and angle identified by sun-synchronous superposed epoch differentiation for solar wind directional information. analysis and be removed from the data. The signal This will either be a reconfiguration of the ion sensor depends on solar angle incidence (power generation) modes, or a combined use of the ion and electron and battery state of charge which, in turn, depends on sensors. An alternate scenario in the trade space would internal power draw and thus controls the number of be to develop mission design tool automated scripts strings producing current and shunt operation. This that would switch the instrument between solar wind signal can be cleaned in a dynamic way with and magnetospheric modes based on lunar wake techniques that exist but have yet to be implemented predicts and entry/exit into the magnetosphere. operationally and distributed widely.

5.2 Magnetometer noise removal 5.3 Shadow spin rate changes The FGM instrument (Auster et al., 2008) is The spin-stabilized ARTEMIS probes use sun subject to power system current interference at a level sensors as their primary means of attitude (spin phase) of 60pT peak-to-peak (Figure 5.1). As the internal information. When the probes enter shadow, the sun power system currents change, noise removal has to be pulse is lost and the last known spin period is used to applied piecewise to ensure the noise signal retains the sector the particle counts, compute the spin-average same properties throughout the selected cleanup magnetic field and despin the data on the ground. For interval. If left uncleaned, the signal appears as a spin- heliophysics investigations, cleaning up shadow tone and its harmonics, affecting the magnetotelluric period data is not critical. This is because especially at investigations in the 0.1 -10Hz range. Power system large lunar distances where refilling is more evident, changes (one or more array strings off-line/shunting) the lunar wake lies outside the lunar shadow, i.e., the also affect the DC level of the magnetometer. typical solar wind flow direction, ~4o away from the Although the THEMIS magnetometer team has Sun-Moon line, enables sunlit wake crossings. developed techniques for recognizing and removing However, shadow period spin phase determination is the spurious signals, these techniques have not been an issue critical for planetary science, because crustal implemented due to resource constraints and because fields extend furthest on the nightside, and these are these spurious signals do not affect heliophysics precisely the periods of highest science return. science. For planetary studies, implementation Cleanup is possible by modeling spin rate changes becomes essential. (Figure 5.2). An alternate, and likely more robust, The SST instrument has much higher sensitivity despinning method while at the Moon would be to use than the ESA instrument and operates at energies the nearby illuminated probe to determine the actual

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magnetic field direction, correlate with the shadowed approved by the Planetary Division, optimization of probe to determine the actual field direction and from the nominal trajectory for planetary objectives will this determine the spin period at all times. This has not occur in FY10 and FY11, i.e. prior to lunar insertion, yet been tested because to date there have been no and will be adjusted and maintained in FY12 based on shadowed intervals in which the two spacecraft were actual flight data from the redesigned orbits. Section in close proximity; however the team can use the lunar 6.9 itemizes the tasks to be accomplished under flybys in 2010 to develop and validate the procedure Planetary funding. ahead of lunar orbit insertion. 6.1 Observatory and instrument status As of this writing, all five THEMIS spacecraft, including the two probes slated for ARTEMIS, are in place and in excellent health, conducting the final (dayside science) portion of the nominal THEMIS mission, while the two probes slated for ARTEMIS move toward the Moon. Automated operations support routine data collection. Probe and instrument status is updated with real-time pass-supports, see http://soleil.ssl.berkeley.edu/ground_systems/themi s_constellation_status.html. Three instruments suffer from minor contamination effects. As expected for the THEMIS SST and typical for all solid-state detectors, sunlight affects two sectors per spin of one out of four SST detectors. Spin harmonics and 32 Hz noise affect the SCM. An 11 Hz tone from sector processing and power system currents affects the FGM. Post-processing software already eliminates the first two problems, while the third is suppressed completely by careful selection of the spacecraft spin rate to avoid beating of the sector clock with the FGM Figure 5.2 Top panel: A model fit (red) to spin period drive frequency – this is done by a spin-change variations determined from magnetic field maneuver, once any major maneuvers are completed observations (green) as the THEMIS spacecraft enter and the probes are to enter a prolonged intervals of and exit shadows (bounded by the vertical lines). The science observations. In-orbit tests have demonstrated spacecraft’s spin period decreases due to thermal that spin-rate changes during shadows on the order of contraction of the wire booms in shadow. Bottom 1-2 hrs (the length of typical shadows in lunar orbit) panel: The black trace shows the duskward component will not re-introduce inordinate noise power. of the magnetic field determined by using the “last The low amplitude FGM noise at the spin tone and known” spin period prior to shadow entry to despin its harmonics is inconsequential for heliophysics the data. The on-board fiducial sun-pulse time drifts science but important for magnetotellurics and crustal from the actual sun direction by 10o-20o/min as the field remote sensing, planetary science objectives. spacecraft spin period decreases. The red trace shows Techniques that remove the noise have been devised results determined when the modeled spin period is and proven to work in principle. They will be used to despin the data. By modeling spin period implemented as discussed in Section 5.4. Sun pulse changes during shadows, we can develop a recovery leads to spin phase recovery. Reprocessing standardized code to remove the “ripple” effect. of distribution functions and moments results in nearly full recovery of shadow data from all instruments except from the electric field antennas. Instrument 6. Mission Operations: operation personnel will restore the Level 1 data in Status and Planetary Tasks accordance with modeled spin phase information. Instruments operate in Slow Survey (SS) mode This section covers the status of the ARTEMIS most of the orbit, and in Fast Survey (FS) mode during flight hardware and mission operations, and the time-based, prime-science intervals (~3 hrs/orbit). anticipated work that will enable the planetary science Marked by the horizontal yellow, red and black bars in observations discussed in Section 3. The ARTEMIS the overview plots at: mission profile is shown in Figure 6.1. The profile and http://themis.ssl.berkeley.edu/summary.php, they orbits have already been optimized for heliophysics. If will also be used to denote data collection modes

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during the ARTEMIS mission. On-board events such to support THEMIS. The NTR T-1 line from GSFC to as high particle fluxes, or low frequency field events the MOC over the Open IONet and 3 voice loops at (e.g. north/south magnetic field turnings in the the MOC continue to function nominally. magnetotail), can be used to trigger 8-12 min Particle 6.3 Prime mission operations (FY07/08/09) Bursts (PB); while high frequency wave power During the first year of operations (Feb 07 – Feb intervals can be used to trigger 3-6s Wave Bursts 08), the five THEMIS probes underwent a combined (WB). Planetary investigations will require an 176 thrust operations, most for probe ascent to final additional, low-altitude FS and burst mode that is time positions. Instruments were turned on and based (Section 5) and that will be implemented commissioned, while both magnetometer and all six operationally using standard practices from THEMIS. EFI booms deployed flawlessly on all probes. Instrument parameters (ESA plate voltages, SST bias 6.2 Status of ground systems voltages, EFI bias current) were configured nominally, All data processing and software continue to and undergo routine periodic tests. In the second year function reliably. All flight dynamics systems are of operations, the mission design team optimized the nominal. Mission design runs with the latest orbit second tail season by adjusting probes P1 and P2 solutions are repeated regularly, covering the entire inclinations and apogees to obtain higher quality mission life to reaffirm conjunctions, shadows and conjunctions within Earth’s magnetotail, based on fuel budget. Product generation, based on updated results from the first tail season indicating that the ephemeredes, is fully automated. Coast phase orbit current sheet was much thinner than previously design telemetry files are transferred post-pass from anticipated. This resulted in a significantly higher the ground stations to UCB, checked and archived. science yield for the second tail season. Additional Level 0, 1 and 2 data processing is automated. mode changes for radiation belt, tail, and dayside Instrument scientists (“tohbans”) review survey plots science resulted in ~100 Instrument Configuration within ~1 day after receipt of data on the ground. See: Change Requests, all successfully implemented. This at: http://sprg.ssl.berkeley.edu/~themistohban/ for demonstrates the tight integration of the instrument tohban functions. The Berkeley ground station science team with mission and science operations that continues to function well. NASA Ground Network will effectively serve the needs of ARTEMIS. stations continue to support THEMIS nominally, while 6.4 Translunar Phase (FY10) Universal Space Net has been certified and has started Once the ARTEMIS tail season begins, a number

23 Figure 6.1 Overview of mission profile for ARTEMIS

of maneuver “tweaks” will be needed to adjust the 5.) and will result in new orbit elements for the lunar three inner probe orbits and keep them fixed in portion of the mission. Orbit insertion to the new sidereal orbits. A large inclination change maneuver elements will be implemented by the operations team planned for P1 and P2 in the late summer of 2008 will at no appreciable additional effort. counteract lunar perturbations of the orbit planes in 6.7 Lunar Orbit (LO) phase time for the 2nd tail season. We will conduct The near-equatorial lunar orbit design, currently significant maneuvers to increase P5’s orbital period, aimed towards heliophysics goals, simultaneously resulting in conjunctions with the other probes each 8, optimizes science return and reduces mission 4, and then 8 days, in the forthcoming 1st dayside, 2nd operations complexity: P1 is retrograde and P2 is tail, and 2nd dayside seasons, respectively. A total of prograde, such that the orbits precess ~360o relative to ~50 nominal maneuvers are expected in the next 1.5 each-other in the proposed 17-month long lunar orbit years. Depending on 1st year results, a small number phase, providing a wide range of inter-probe (3-5) of additional orbital adjustments for enhanced separations and longitudes as needed for the science science (e.g. to ensure prolonged neutral sheet objectives. The fast relative precession of P1 and P2 encounters for P1 and P2) may be needed. removes the inertial longitude of insertion (and time of 6.5 Lissajous Phase (Q1,Q2 of FY11) LOI) from the design considerations. The team has The mission design and operations plan for found additional implementation options that even-out ARTEMIS calls for raising the apogees of P1 and P2 the fuel margin (shown in Table 7A) between the two and using lunar and Earth flybys to insert the probes probes and fine-tuned the DSN contact schedule. into weakly stable orbits at the two Earth-Moon Optimization for planetary objectives is discussed Lagrange points, LL1 and LL2, approximately one in Section 5. It is evident from Table 7A that the year after the initial Earth-departure operations, i.e., at probes have sufficient fuel margins to ensure re-entry the start of FY11. After a 5-month residence at the by periselene reduction (10m/s) as necessary at end- Lagrange points, the probes are inserted into stable, of-mission. Operationally, an inclined orbit, optimal 27hr period, near-equatorial lunar orbits, for ~17 for planetary) results in gravity-gradient torques months of operations, i.e. until the end of FY12. (15deg/year worst case for a 26deg inclination orbit) Science optimization of this orbit sequence has taken which perturbs the spin axis away from the science place since April 2005. attitude. This requires 225grams of fuel per year to At the Lagrange points the probes execute correct, which is equivalent to 5m/s per year of ΔV Lissajous orbits with ~14 day periods. The Lissajous and can be afforded for a number of years by both P1 orbit phase design has a dual goal: Operationally, it and P2. This tentative planetary mission design prepares the team for accurate, low risk orbit insertion, concept leaves sufficient fuel to ensure stationkeeping while orbit evolution flattens the orbit of P2 after its maneuvers, which may be needed for an extremely previous out-of- (ecliptic) plane motion (Figure 6.1). low periselene (~50km). The long term orbit stability Scientifically, this phase is important for Heliophysics to Earth perturbations and inclination/APER drifts science, as it results in a wide range of large inter- have to be considered as part of a trade study. probe separations (10-20 RE) and Sun-angles, suitable The ARTEMIS probes will be operated in the for studies of large-scale phenomena in the standard SS, FS, PB and WB modes used for magnetotail, solar wind, and lunar wake. There are THEMIS. Planetary science requires approximately two Lissajous orbit sub-phases, driven by heliophysics 0.5hrs of FS mode data at periselene, whereas science reasons (above): From late October 2010 to heliophysics science requires 2.5 hrs in the wake. This early January 2011 the probes are on opposite sides of results in a data volume one fourth that of THEMIS at the Moon; from January 2011 to early April 2011 the Earth. We anticipate only two PBs per orbit: one probes are on the same side. time-based at periselene and one on-board-trigger- 6.6 Lunar Orbit Insertion (LOI) based closer to aposelene. Burst selection will occur at The orbit insertion times and inclinations are ARTEMIS mission and science operations meetings, flexible and chosen to optimize the lunar orbits for incorporating a planetary scientist and a heliophysics heliophysics science. Once the sequence commences scientist, the mission tohban, and the instrument and the closest approach is reached, a series of critical scientists. Planetary requirements will be operations, namely periselene and aposelene burns, accommodated and adjusted as a result of these result in orbit capture. Planetary science would benefit deliberations. from a higher inclination and lower periapsis, ARTEMIS will use the DSN 34m BWG antennas assuming orbit stability and fuel margins are for communications at 3.5 hrs/probe/2 days. The maintained. The redesign of the lunar orbit insertion to proposed DSN pass duration allows 0.5hr of use by a optimize the lunar orbits for Planetary science will be range channel for orbit determination purposes, the topic of a science optimization trade study (Section followed by a transition into a 3hr-long, science

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telemetry recovery mode. At a maximum lunar range considered and routine orbit forecast runs are needed of 64 RE with the known G/T of the DSN 34m BWG to safely plan low periapses. Fuel budget and stations, we obtain: management of other mission resources (power, • DSN, science: 65.536 kbps / 3.2 dB margin thermal, data volume, observation time, geographical • DSN, ranging: 16.384 kbps / 2.1 dB margin coverage) are key. Science trades can mitigate risk, Assuming that 32kbps represents a worst case therefore the trade space between science yield, scenario for reasonable lunar orbit view-angles from operational costs and technical risk mitigation will be Earth (~5o to ecliptic), and spin-axis tilts planed for looked at very carefully for optimal science return. science operations (~8o to ecliptic) regardless of orbit Efficient operations factor highly in the overall cost- inclination, we observe that we can collect ~337.5 science-benefit analysis of the mission. Mbits / 3 hr contact. This exceeds mission requirements by more than a 50% margin. 6.9 ARTEMIS flight operations and scheduling As the probe apogees increase, the transition from 6.8 ARTEMIS Mission Design and Navigation operations using the Berkeley Ground Station to the The ARTEMIS science and mission Deep Space Network is proceeding very well. implementation teams (UCB, JPL, GSFC) are holding Telemetry, Commanding, Doppler and ranging tests weekly telecons to further solidify the ARTEMIS with both THEMIS B and C were already very mission heliophysics design. JPL has completed successful and final DSN certification for ARTEMIS delivery of the end-to-end mission design plan, operations has been completed. While command and including bias maneuvers, and currently participates telemetry tracking can be accomplished with BGS nominally in telecoms for cross-checking and until the translunar phase, DSN use will be continued maintaining the designers’ knowledge base. Maneuver through the summer for practice runs. In the translunar independent validation, navigation error phase, routine operations on a best effort basis by characterization, and insertion of additional trajectory DSN will continue, in order to maintain proficiency of correction maneuvers are currently under way at both personnel in operations until the prime science phase GSFC (for proof of principle and spot-checking) and at the start of 2010. Apart from the Lunar Orbit UCB (for detailed design) with identical tools. In Insertion there are no major critical maneuvers in the particular, propagation of targeting errors and mission. It is important, however, to maintain backups orbit/attitude knowledge errors on mission design is and contingency plans for the Orbit Raise Maneuvers currently under way. (ORM), because the mission design is based on a “Return to Nominal Trajectory” plan, which relies on successful execution of the ORMs with accurate targeting (<1%). This is accomplished by scheduling at least one backup ground station, and ensuring that schedule information and console personnel are in place a few hours prior to each planned pass. Flight operations for planetary require accommodating the new instrument modes (or revised regions of interest, see Section 5.3), new burst collection and ensuring that temperature and sun-angle limits are not violated in slightly inclined orbits. These require flight software changes, flatsat testing and spacecraft uploading and verification. Subsequently, Table 6.1 P1, P2 have started their journey to the instrument personnel are expected to validate the new Moon. The insertion scenario can be further modes in the lunar environment, ensure instrument optimized, but has sufficient margin for either de-orbit configurations are working properly in the various (~10m/s) or for operational use for planetary geophysical regions, and that the science return from objectives. reconfigured instruments satisfies the needs of the proposed ARTEMIS planetary investigation. Planetary objectives require re-targetting the Lunar 6.10 Summary of Mission Operations tasks Orbit Insertion (LOI), as explained in Sections 5.1 and The ARTEMIS design for heliophysics is already 5.2. This has negligible operational effects on the mature and under way. The planetary implementation actual implementation of the LOI (Section 6.6). has an identified tentative solution in line with current However, choices of inclination and apo/periselene heliophysics operations plans, and within the fuel affect probe stationkeeping at the Moon. Orbit / capabilities of the ARTEMIS probes. It will be vetted attitude determination tolerances have to be with the ARTEMIS science team, composed of

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leading experts in planetary and lunar science. In software and science team, and very efficient summary, the Mission Operations tasks to be done are: communications between the analysis and instrument • Implement shadow spin phase recovery scientist teams. These principles will guide the • Orbit detailed redesign of LOI for planetary ARTEMIS operations team. • Spin axis reorientations / periapsis tweaks • Planetary modes test/implementation • Instrument operations/mode validation

Figure 8.1 Special publications on THEMIS from the early part of the mission. Left: Mission, instruments and first results (Space Science Reviews, 2008). Right: Initial discoveries from the string-of-pearls configuration, a.k.a. coast phase of THEMIS, prior to probe ascent to their tail-aligned configurations (Geophysical Research Lett., 2009).

8. Prior Results, Community Support The THEMIS team has made significant discoveries in the last 2 years in the areas of magnetospheric substorms, inner magnetosphere science, and dayside science. Between launch and August 2009 the team has published about 100 papers, including a special issue of Space Science Reviews, and a special issue of GRL (Figure 8.1) Specifically the recent THEMIS results have identified magnetic reconnection as the origin of Figure 8.2 Significant THEMIS discoveries. Left: substorms in the tail (Angelopoulos et al., 2008), and First identification of substorm trigger in the tail by discovered the of dayside chorus waves at quiet times THEMIS resulted in a Science cover publication in (Li et al., 2009), see Figure 8.2. August 2008. Right: Identification of quiet time chorus THEMIS has also made significant progress in waves at the dayside magnetosphere resulted in a identifying the elusive origin of plasmaspheric hiss. Geophysical Research Letters Cover paper (May ‘09). This is an electromagnetic emission in the near-Earth environment that has been known through ground In particular THEMIS has released all its software observations in the audio range for almost a century, tools to the community and has made public all its but only now discovered to be generated by bursts of high resolution data through a number of data servers waves further away from Earth, called chorus waves around the US and abroad. On line software tutorials (Figure 8.3, left). In the ionosphere, the spectacular are available at http://themis.ssl.berkeley.edu, and swirls of auroral light often seen in the course of software demos are held at major scientific meetings storms have finally been linked to similar vertical (biannually). Machine-independent, IDL-based code plasma flows in the magnetosphere (Figure 8.3, right). can read standard CDF files and is freeware capable These exciting research advances were made possible (IDL Virtual Machine), though 100 IDL licences have thanks to flawless mission operations, an open-data been distributed by the THEMIS team to the philosophy, a well coordinated and highly talented community for analysis. The team has developed a

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Graphical User Interface (GUI) to ease novice IDL exchanged amongst scientists and strengthen users into THEMIS analysis (Figure 8.4). The GUI is collaborations or exchange of tools and ideas. based on a Data Analysis tool called SPLASH which is already working for Planetary Data Analysis (Galileo/Jupiter, Cassini/Saturn) and can readily ingest Planetary Data System files. All data/plots are available on-line and calibrated one day after downlink (http://sprg.ssl.berkeley.edu). Seamless data distribution through the IDL software happens via HTTP or FTP socket connection. Bundled downloads via the UCB site are also available on-line at VMOs and are SPASE compatible. PDS downloads will be available as part of this proposal. Software is managed by SVN and allows users to develop and submit their own contributions for distribution to the community. Community support is available through our help line: [email protected]

Figure 8.4 Left: On-line overview plots are processed and calibrated only hours after collection and appear on-line as overview plots available for event-selection and instrument check-out by a curator (“tohban”, see: http://sprg.ssl.berkeley.edu/~themistohban). Right: THEMIS software can be run on any platform that IDL runs on, and will automatically load the data with remote http or ftp connection. An IDL-based GUI creates publication quality plots of all the data Figure 8.3 Significant discoveries from THEMIS in available, including ground based or ancillary the inner magnetosphere. Left: THEMIS spacecraft spacecraft data with intuitive button selections. discover the origin of plasmaspheric hiss (from Installation is simple; tutorials are available on-line. Bortnik et al., Science, May 2009). Right: THEMIS finds the first correlation between auroral vortices in 9. Public Affairs and EPO the ionosphere and plasma vortices in space (Keiling 9.1 Recent Public Affairs Activivies et al., JGR, 2009, and European Geophysical Union A vigorous public affairs program at NASA/GSFC press conference, Vienna, Spring 2009). with the help of the Scientific Visualization Studio, has achieved remarkable successes during the past 2 As a result of the above open data policy and years. The THEMIS launch was covered extensively community engagement, more than 90 papers have by the media and the launch video was advertised by been written on THEMIS in the 2.5 years since launch, www.nasawatch.com and received more than 21,000 many of them not funded directly by the THEMIS hits on “YouTube”. The Fall 2007 AGU new results project. Additionally, other data centers press conference was well attended and was well (NOAA/SPIDR, GOES) have expressed interest in covered by the print media. It resulted in numerous creating data-ports with http/ftp sockets into the interviews broadcast by BBC, CBC, and NPR, THEMIS analysis system. Thus the team has including a feature on the NPR program Earth & Sky. experience in ingesting and interfacing with diverse Two presentations at the Maryland Science Center, (in datasets and supporting the entire heliophysics 2007 and 2008) and at the Smithsonian brought the community. excitement of science to the general public. PBS’s This practice will continue on ARTEMIS. The Newshour presented a special report on our E/PO dataset and analysis tools will be an extension of the efforts to engage Alaskan students and is preparing a THEMIS dataset. We will offer to integrate LRO and follow-up program. The NOVA channel repeatedly LADEE analysis tools into the THEMIS/ARTEMIS aired a THEMIS story on magnetic storms (Figure 9.1) analysis system. We will standardize PDS data entries while popular science magazines have captured into the system, and make available .LBL and .TAB THEMIS discoveries and extended the message of formatted ARTEMIS Level-2 data to PDS. “Crib” NASA’s successes to the public. Astronomy Magazine sheets that contain processing or plotting code can be rated the THEMIS discoveries one of the top 10 stories in 2008 (Figure 9.2).

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physical science. Figure 9.3A shows the locations of the 12 schools in 10 US states that host our research- grade magnetometers and participate in our E/PO program. We hold yearly workshops for the teachers, make the magnetometer data available on the web in real-time, and develop, test, and revise teacher guides (see Figure 9.3B). We actively maintain a website (http://ds9.ssl.berkeley.edu/themis/) that provides comprehensive information for the public, students, and teachers as well as EPO evaluation results. THEMIS is equally interested in higher education. Table 9.1 is a breakdown of the 47 young scientists (24 in the US) supported by the project.

Country Under Grads Post- Research grads docs Associates Figure 9.1 NOVA series aired a story on THEMIS Austria 1 1 discoveries and magnetic storms with footage from the Canada 1 7 4 3 UCB Mission Operations Center. Germany 1 2 Russia 1 2 These results bespeak of an public affairs team that USA 3 9 11 1 is well positioned to carry the ARTEMIS message of Table 9.1 Young scientists supported on THEMIS. innovation and discovery to the public, to inspire the nation and motivate the next generation of scientists and engineers.

Fig. 9.3A. Blue dotes indicate the locations of schools with magnetometers;, red dots indicate science observatories.

We will broaden the THEMIS Fig. 9.3B An example of a THEMIS teacher’s content to discuss planetary guide that will be used in objectives, such as the formation the future programs. of the Earth-Moon system, and planetary evolution. ARTEMIS content will include space hazards for astronauts on their way to the Moon and Mars. We will expand the program’s beneficiaries by collaborating with other E/PO partners, on LRO, LADEE and the ILN and also address an African American audience.

10. References (Terse) Adams, J.B., and T.B. McCord (1971a). Science, 171, 567. Adams, J.B. and T.B. McCord (1971b). LPSC 2, 2183. Angelopoulos, V. (2008). Space Sci. Rev., 141, 5. Figure 9.2 Left: Jim Lehrer show on THEMIS Ground Auster, H.U., et al. (2008). Space Sci. Rev., 141, 235. Magnetometers observing space currents in the Berg, O. E., et al. LNP Vol. 48, 48, 1976/1/1. classroom. Right: THEMIS discoveries were amongst Bonnell, J.W., et al. (2008). Space Sci. Rev. 141, 303. the top 10 stories in Astronomy magazine in 2008. Bortnik, J., et al. (2009). Science, 324, 5928, 775.

Cisowski, S. M., et al. (1983). JGR, 88, 691. 9.2 EPO Plans Cladis J.B., et al. (1994). 99, 53-64, 1994. The main goal of our E/PO program is to help Coleman, P. J., et al. (1972). LSC 3, 2271. inspire rural and Native American high school Colwell, J. E., et al. (2005). Icarus, 175, 159. students to become engaged in Earth, space and

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11. Acronyms NOAA National Oceanic and Atmospheric AGU American Geophysical Union Administration ALSEP Apollo Lunar Surface Experiments NPR National Public Radio Package NRC National Research Council ARTEMIS Acceleration, Reconnection and NSF National Science Foundation Turbulence, and Electrodynamics of P1,2,3,4,5 THEMIS probes 1,2,3,4,5 corresponding to Moon’s Interaction with the Sun letters B, C, D, E, A BBF Bursty bulk flow PBS Public Broadcasting System CNN Cable News Network Pc 1 Continuous pulsations, period 0.2 to 10s CRATER Cosmic Ray Telescope for the Effects of RE Earth radius (radii) Radiation RL Lunar radius (radii) DC Direct current Rx Reconnection EFI Electric field instrument SCM Search coil magnetometer EMIC Electromagnetic ion cyclotron SDO Solar Dynamics Observer E/PO Education and public outreach SDT Science Definition Team ESA Electrostatic analyzer SELENE SELenological and ENgineering Explorer FAC Field-aligned current SOC Science Operations Center FGM Fluxgate magnetometer SOHO Solar and Heliospheric Observatory FY Fiscal year SPDF Space Physics Data Facility GBO Ground-based observatory SSE Selenocentric solar ecliptic GEONS Geomagnetic Event Observation Network SSR Space Science Reviews by Students SSL Space Sciences Laboratory, UC Berkeley GEOS Geostationary Scientific Satellite SST Solid state telescopes GI Guest investigator STEREO Solar Terrestrial Relations Observatory GOES Geostationary Operational Environmental SW Solar wind Satellites THEMIS Time History of Events and Macroscale GPS Global positioning system Interactions GRL Geophysical Research Letters TLI Trans-lunar injection GSE Geocentric solar ecliptic UCB University of California, Berkeley GSFC Goddard Space Flight Center UCLA University of California, Los Angeles GSM Geocentric solar magnetospheric HF High frequency HPS Heliophysics HQ Headquarters IMF Interplanetary magnetic field ILN International Lunar Network JGR Journal of Geophysical Research KeV Kiloelectron volt LANL Los Alamos National Laboratory LL1 Lunar libration 1 point (between Earth and Moon) LL2 Lunar libration 2 point (along Earth-Moon on other side of Moon) LP Lunar Prospector LPSC Lunar and Planetary Science Conference LRO Lunar Reconnaisance Orbiter LSC Lunar Science Conference MeV Mega electron volt MHD Magnetohydrodynamics MHz MilliHertz MOC Mission operations center NAC NASA Advisory Council NASA National Aeronautics and Space Administration NLSI NASA Lunar Science Institute

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Addendum: Expanded Reference Section Dyal, P., C.W. Parkin, and W.D. Daily (1974). Magnetism and the interior of the moon. Rev. Geophys. Space Adams, J.B. and T.B. McCord (1971a). Alteration of lunar Phys., 12, 568-591. optical properties; age and composition effects. Science, Farrell, W. M., T.J. Stubbs, R.R. Vondrak, G.T. Delory, and 171, 567-571. J.S. Halekas (2007). Complex electric fields near the Adams, J.B. and T.B. McCord (1971b). Optical properties of lunar terminator: The near-surface wake and mineral separates, glass, and anorthositic fragments accelerated dust. Geophys. Res. Lett., L14201, from Apollo mare samples. Proc. Lunar Planet. Sci. doi:10.1029/2007GL029312. Conf. 2nd, 2183-2195. Farrell, W. M., T. J. Stubbs, J. S. Halekas, G. T. Delory, M. Angelopoulos, V. (2008). The THEMIS mission. Space Sci. R. Collier, R. R. Vondrak, and R. P. Lin (2008). Loss of Rev., 141, 5-34. solar wind plasma neutrality and affect on surface Auster,H.U., K.H. Glassmeier, W. Magnes, O. 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