GEospace Magnetosphere-Ionosphere-Neutral Interaction (GEMINI) A science mission framework targeting the core of the globally coupled magnetosphere-ionosphere providing continuous data optimized for global model validation D. Mitchell (JHU/APL), P. Brandt (JHU/APL), E. Donovan (U. Calgary), M-C Fok (GSFC), S. Fuselier (Lockheed), D. Gallagher (MSFC), J. Goldstein (SwRI), J. Kozyra (U. Mich), R. Meier (NRL), S. Mende (UCB), T. Moore (GSFC), P. Newell (JHU/APL), S. Ohtani (JHU/APL), G. Parks (UCB), L. Paxton (JHU/APL), T. Sotirelis (JHU/APL), J. Spann (MSFC), R. Wolf (Rice) Introduction The Solar System is comprised of a collection of coupled systems. In fact it is one large system-of-systems in which the Sun is the primary source of energy. Earth, as our home, is the planet we know most about. We have ventured extensively into Earth’s immediate surroundings, called Geospace, and have learned how Geospace is intrinsically interconnected over diverse scales of space and time. Over time an armada of spacecraft have revealed extraordinary global phenomena such as geomagnetic storms, with plasma energized in the magnetosphere distorting its magnetic and electric fields leading to strong modification of the radiation belts, and ionospheric storms, in which large regions of Earth’s ionosphere are redistributed over the globe. Plasma and fields in both the ionosphere and magnetosphere are coupled with each other and multiple processes (precipitation, Joule heating, particle acceleration, wave generation, mass outflow) are competing simultaneously on global and local scales to produce the global phenomena we observe. Such a system requires simultaneous global and continuous measurements of the critical regions of the magnetosphere and ionosphere. By the very nature of coupled systems, observation of the relationships among components is critical to understand and characterize the collective behavior. Imaging is the most effective (and arguably the only) way to carry out such system-level observations. Understanding of the complex interrelationships is impossible without a global view of Geospace. Imaging provides more information than any practical number of distributed single-point measurements and therefore is indispensable for system-level exploration. In this paper, we outline a science mission framework that targets the core of the globally coupled magnetosphere- ionosphere system from two platforms in a high circular orbit, providing continuous data optimized for global model validation. A range of outstanding mysteries in space physics drives the choice of observational targets. Planetary magnetospheres are efficient particle accelerators, generating a “ring current” that couples the inner magnetosphere with the ionosphere, and produces field distortions and wave activity leading to dramatic radiation belt intensification. In ionospheric storms, plasma is redistributed globally by magnetospheric as well as solar wind driven currents, auroral precipitation and solar irradiation, disrupting communications and navigation systems. GEMINI targets the ring current, plasma sphere, aurora, and the ionospheric-thermospheric plasma redistribution through continuous imaging of both northern and Figure 1: GEMINI targets the core of the coupled magnetosphere-ionosphere system by providing global, southern auroral emissions; mid-latitude far continuous 3D images of the ring current (orange), plasma ultraviolet (FUV) imaging; stereo extreme sphere, aurora, ionospheric-thermospheric dynamics and flows. ultraviolet (EUV) imaging of the plasmasphere; and GEMINI obtains the collective behavior of the complex, coupled, stereo energetic neutral atom (ENA) imaging of the interconnected Geospace system and the measurement resolution ring current and the near-Earth plasma sheet. enabling global model validation and discovery science. These measurements are made together with ground-based radar (both HF SuperDARN and ISR such as AMISR), auroral imaging arrays, and magnetometer chains) as well as other existing space assets such as IRIDIUM/AMPERE, DMSP, GOES, LANL, GPS, whatever is upstream, and any NASA Explorers or other Earth magnetosphere/ionosphere missions that may fly contemporaneously. With ground-based and LEO data providing detailed information on field aligned currents, ionospheric electron densities, temperatures and flows, GEMINI will provide the means to link the global scale magnetospheric state with these detailed ionospheric conditions. Global modeling and assimilation is a core part of the GEMINI concept. We have reached a stage where we no longer can understand the behavior of geospace without the use of physical models to retrieve the mechanisms that compete simultaneously on several scales. Meanwhile, the existing global models are continually starved for global data against the models can be validated. Imaging plays a natural and necessary role in providing global validating observations of system level interactions and processes that are not possible otherwise. Dynamics Explorer made a good beginning to the investigation of this coupling. DE imaging and ionospheric and magnetospheric in situ observations gave us a simultaneous view of small-scale physical processes and geospace at the system-level, albeit projected onto the 2D ionosphere. The DE images provided context, and more importantly, they provided our first means of assessing how the smaller scales probed by the in situ observations coupled to the larger system. ISTP took this to another level, using multiple coordinated in situ probes in combination with auroral imaging. The IMAGE Explorer mission expanded the kinds of imaging available to characterize the global scale of the Geospace system, adding magnetospheric energetic ENA and plasmaspheric EUV imaging to the FUV imaging that had been used on the earlier missions. And the many in situ measurements provided by FAST, DMSP, Polar, Geotail, and other missions provided the means of assessing how the smaller-scale processes drove (or were driven by) the larger scale system. Features as fundamental as plasmaspheric drainage plumes (which were still argued about until the IMAGE EUV images proved their existence), the local time distribution of the partial ring current (which was shown by ENA imaging to vary between early morning and dusk from one storm to another), and the substorm acceleration of oxygen in the context of storms (revealed by ENA imaging) became instantly clear using the IMAGE global images. Combined with in-situ measurements it provided the global context required to interpret the in-situ measurements correctly. For example, was a spacecraft inside or outside of the partial ring current? Where was the plasmapause relative to the spacecraft measuring a particular plasma wave signature? Mission Objective and Science Questions GEMINI seeks to determine how the Figure 2. The magnetosphere-ionosphere-thermosphere system is complex. magnetosphere-ionosphere-thermosphere Global scale measurements are critical to placing in situ (HEO, MEO, and LEO) system is coupled and responds to solar and and ground-based measurements in an appropriate framework. Global models are strongly constrained by global scale imaging. The combination (global magnetospheric forcing and to provide a imaging, in situ, ground based, and models) will enable understanding the long-duration mission framework into coupling among these interconnected plasmas. which additional science missions can naturally fit. GEMINI’s science questions are chosen to address critical pieces in the global redistribution, acceleration and response in the magnetosphere and IT system as illustrated in Figure 2. We discuss these overarching science questions in terms of the global system and identify “ports” where external science investigations fit in naturally, enabled by GEMINI’s long lifetime. 1. How does MI-coupling control plasma redistribution in the magnetosphere and ionosphere/thermosphere? (GEMINI) Both magnetospheric and solar forcing gives rise to IT plasma redistribution. Plasma accumulation in the afternoon/dusk sector at low latitudes appear to be funneled to higher latitudes that eventually reach the cusp, where most of the ionospheric outflow is seen in statistical studies. Is this snaking pattern a how plasma is supplied to the breathing hole of the Earth’s ionosphere to space? The funnel coincides with the Sub-Auroral Polarization Stream (SAPS) channel, which appears almost perfectly reflected in the plasmaspheric drainage plume in the magnetosphere. The SAPS phenomena is believed to be an effect of the closure of the ring current through the low- conductance gap in the ionospheric trough region, which leads to Figure 3: Strong ionospheric flows (SAPS) is enhanced ionospheric flows in a narrow region. Fundamental plasma only one example of a coupled phenomena physics mysteries are nicely illustrated in this interface region. As that requires simultaneous imaging of both magnetospheric currents close through the different and dynamically the magnetospheric “driver” and the changing conductances of the ionosphere, the global electric field of ionospheric response. The SAPS flow is an the ionosphere is altered and feeds back to the large-scale electric field effect of magnetospheric currents closing of the magnetosphere producing macroscopic effects in the location through the low-conductance ionospheric and dynamics of both the ring current and the plasma sphere. Defying trough region [Brandt et al., 2008]. expectations that the ring current would shield the inner magnetosphere through these coupled processes, E-field in the equatorial magnetosphere displayed the opposite behavior, with surprisingly strong E-fields found very deep in the magnetosphere. The complicated MI-coupling also modifies important boundary regions such as the overlap between the hot and cold plasma of the ring current and plasma sphere, critical for wave growth that can accelerate electrons to high energies. The dense plasma of the plasma sphere is further stretched out in EUV-visible plasmaspheric drainage plumes that reach the dayside magnetopause, where the presence of heavy ions may regulate the dayside reconnection rates. 2. What are the processes governing ionospheric outflow from the polar ionosphere and its subsequent acceleration in the 5000 km gap region that transports it to the magnetosphere? (External investigations needed) After ionospheric plasma has been redistributed to higher latitudes, other processes take over that accelerate ions to escape energies. This acceleration region has seen very scarce measurements, impacting our ability to reproduce how ionopsheric plasma populates the magnetosphere and leaving a gap in our understanding of when/how the ring current becomes dominated by heavy ions from the ionosphere (O+). Addressing this critical question requires addition satellites taking measurements in this critical altitude range (5000-10000 km altitude), a good example of how a separate or coordinated mission might naturally fit in to the global science framework of GEMINI. 3. How is hot plasma created, accelerated and transported to the inner magnetosphere to form the driving plasma pressures of the plasma sheet and ring current and how do these couple to the ionosphere? (GEMINI HEO only) Both ionospheric and solar wind plasma are believed to enter through the flanks of the magnetosphere from where it is transported in to the magnetosphere. While terms such as “storm convection” and “substorm injection” have been used to represent the collective mechanisms that are responsible for transporting and heating plasma to the energies that form the driving plasma pressure, observations show no resemblance to a convective plasma bulk motion with negligible response to solar wind driving [Hori et al., 2006] and no resemblance to “fronts” of substorm injections moving earthward, but rather fin-like structures populating the even the deep inner magnetosphere indicating a critical role of plasma instabilities [Ohtani et al., 2008; Yang et al., 2008; Keika et al., 2010; Nose et al., 2010], not unlike what is found at Saturn and Jupiter. Hot plasma represents a gap when it comes to modeling. Magneto Hydro Dynamic (MHD) models capture the global dynamic field variations and their response to solar wind driving, but has no representation of hot plasma. So-called kinetic models (typically solving a bounce averaged Boltzmann equation) reproduce the large-scale features of the ring current provided source populations at its outer boundary, but do not reproduce the field variations required for energizing the hot plasma. To successfully couple these two families of models, model validation against global data is not only desired, but also required. 4. How does coupling between the ionosphere and the magnetosphere control inter-hemispheric currents and structure? Earth’s auroral zones map from the open polar cap at high latitudes to as low as L ~4-5 at low latitudes, during storms. However conjugate imaging of the north and south auroral zones has been only by chance, not design, and so data is sparse and wavelength coverage and spatial resolution poorly matched. GEMINI provides for a long, nearly continuous experiment in which conjugate, full auroral zone images may be analyzed for evidence of direct interhemispheric connection, dynamics confined to one hemisphere only, and north-south asymmetry in precipitation patterns while simultaneously obtaining ring current pressure and composition with stereo ENA imaging and global electric field structure and strength with stereo EUV imaging of the plasmasphere internal structure and flow speeds, drainage plumes, and plasmapause location. An added AMPERE-like capability will enable GEMINI to address how field-aligned currents (FACs) are affected by hemispheric conductance differences. Mission Implementation The GEMINI mission uses two identical nadir-viewing spacecraft in an 8 RE circular polar orbit with variable orbital phase separation to enable global and continuous stereo measurements of the 3D distributions of the ring current pressure and plasma sphere. Auroral and airglow imaging provide nearly continuous and, depending on mission phase, conjugate remote observation of the ionosphere and thermosphere, enabling estimations of the precipitating electron energy flux, ionospheric electron density, and thermospheric composition and energy input. UV analysis techniques now exist to rapidly convert airglow emission intensities into geophysical quantities (e.g., precipitating particle average energy and flux, ionospheric Pedersen and Hall conductivity, and thermospheric O/N2 ratio). Large- scale maps of the spatial, intensity and energy distribution of proton and oxygen precipitation will be made by measuring their small signature Doppler-shifts. This approach enables tracking of dynamical features in the ionosphere, such as polar cap ionization patches, positive and negative storm effects, neutral atmospheric responses to auroral heating, ionospheric scintillations and plasma bubbles. The important coupling components missing from the high altitude measurements will be obtained using GEMINI’s low altitude components, which comprise measurements from a large range of resources including DMSP, IRIDIUM/AMPERE (for global field aligned currents), SuperDARN radar at high and mid latitudes for ionospheric flows and electron density profiles, Millstone Hill and AMISR radar for mid latitude dynamics, GPS TEC maps, and magnetometer and all-sky camera arrays. The result will be global specification of the ionospheric electric field and electric current patterns in both hemispheres, essentially completing the electrodynamic picture at low altitude. A new feature of this mission, enabled by nearly simultaneous observations in both hemispheres, is the ability to investigate the little-understood role of inter-hemispheric asymmetry (due to the tilt of the dipole and rotation axes) on the global system behavior. Mission Strategy • Image the 3D magnetospheric distribution and evolution of critical populations: o The plasma pressure in the plasma sheet and ring current using energetic neutral atoms (ENA) with sufficient temporal and spatial resolution to retrieve the electrical current system that distorts the magnetic field and that connects through the ionosphere producing the electric field o The plasmasphere using extreme ultraviolet (EUV) with sufficient temporal and spatial resolution to retrieve response to the electric field • Image the ionosphere-thermosphere system using o multiple wavelengths of far ultraviolet (FUV) to assess auroral energy input, conductance, IT composition changes and redistribution o multiple radars to image the plasma flow and electron density profiles in order to estimate the ionospheric electric field and constrain conductance o multiple low-flying magnetometers to derive global FAC patterns, such as AMPERE to help constrain ionospheric electric fields o ground based magnetometers to map magnetospheric coupling regions at low altitude o Ground based all-sky camera arrays to obtain high spatial and time resolution auroral configuration and precipitation patterns. Mission Description

• Two High Altitude Spacecraft in ~8RE circular near-polar orbit (continuous and global 3D) o 1 ENA, 1 EUV, 3 FUV cameras per S/C o nadir pointing with yaw about nadir • Ground-based radar network to cover the mid- to high-latitude ionosphere • Existing ground-based magnetometer networks and all-sky camera arrays • Low-altitude satellite component or existing facilities such as AMPERE and Swarm • 2 year life time required, but orbit enables a long-duration (~10 yr) mission • No new technology development • Taurus II provides ample launch capacity; we have book-kept $100M to $130M in the mission costs Attitude Control Requirements (driven primarily by auroral imaging): • Attitude control 0.1° (3 sigma) • Attitude knowledge 0.02° (3 sigma) (after the fact) • Orientation 3-axis with payload sensor axis to nadir Mission Cost (2 spacecraft HEO component only) • Original detailed estimate made in 2003, assuming Delta II 7925. • Current cost estimated using 1.2 (low) to 1.5 (high) inflation across all mission components. • Cost, FY2010 $290M to $405M including 25% reserve, all mission phases; • For 10 year mission, cost range is $350M to $500M Instruments: Component Measurement Mass Power FOV Envelope Bitrate [Heritage] kg Watts (deg) (cm) kbps FUV Oxygen-I (1356 Å) 21 2.4 15x15 80x50x30 40 Spectrographic Proton (Doppler shifted Imager [IMAGE] 1216 Ly-α) FUV 1 LBH long (170-190 nm) 6 1.5 15x15 32x17x18 20

FUV 2 LBH short (140-160 nm) 6 1.5 15x15 32x17x18 20

ENA [Cassini, 2 - 200 keV H, 6.1 3 120x120 40x50x50 20 IMAGE] 10 - 300 keV O 2° ang. res. > 10 keV/nuc. 30 second time resolution EUV 30.4 nm He 30.4 nm 20 20 90x90 50x50x50 10 [IMAGE] Electronics 7.5 11 N/A 23x23x23 0.25

Total 66.6 44.4 110.5 HEO Instruments (2 flight, 1 flight spare for each type): FUV (SI + 2 CAM+ELECTRONICS) $16400K EUV $7800K ENA $17200K GEMINI can be supplemented by any remote or in-situ measurements of plasma, energetic particles, electric and magnetic fields at as many points separated by distances of RE as feasible. Many in situ measurements are generally available from a variety of existing assets (e.g., AMPERE, GOES, LANL Geosynch, GPS, ACE/WIND/SOHO/DMSP (in situ + SSUSI, SSULI)/Swarm, etc.). While ionospheric dynamics can be studied in detail by in situ measurements, valuable complementary tools to obtain medium scale morphology include remote sensing through auroral imaging, ground-based auroral imaging networks and magnetometer networks, as well as radar (both HF, such as SuperDARN including the newer mid-latitude stations, and incoherent scatter, such as AMISR). Global imaging provides the system-level view while high spatial and temporal resolution imaging of more limited regions probe detailed coupling. Simultaneous, conjugate ENA and auroral imaging provides critical information on global ring current evolution and pitch angles, and on how ionospheric conditions differ in the two hemispheres and what those differences can tell us about magnetospheric coupling—in particular, the flow of particles and currents between different parts of the system. Coupling between neutral winds and the ionosphere, serving as either a generator or a load for the magnetosphere, requires measurement of neutral winds at altitudes where neutral-ion collisions are important to transferring momentum between the two populations. This component would require in situ and/or interferometric neutral wind measurements from LEO satellites. While we have not specified a directly funded low altitude component to address the coupling problem, many such components can be envisioned. Our estimate of the GEMINI HEO mission costs places the mission squarely in the low-cost category. This leaves ample room to add a specifically funded low altitude spacecraft, or even pair of spacecraft. For example, one appropriately instrumented spacecraft in a FAST-like orbit could measure ion outflows from the polar cap, auroral zone, and plasmaspheric refilling (addressing science question 2), while also dipping deep into the mid and high latitude ionosphere at perigee to directly measure ionospheric and thermospheric parameters important to establish conductance, heating, current closure, precipitation, neutral wind speeds, etc. Or, alternatively a pair of LEO polar spacecraft could be placed relatively close to each other in longitude to measure longitudinal ionospheric structure and dynamics at, for example, the dawn and dusk meridians. We have not estimated costs for specific LEO satellites, as we consider GEMINI to be a complete mission without them. However, an even more ambitious mission could include some combination of the LEO examples we have suggested, or others we have not mentioned, and probably at an incremental cost that would remain within the medium size range ($500M - $750M). Modeling The coupling problem cannot be understood without a strong modeling effort. A cornucopia of quantitative theoretical models now exists that solve basic equations of the inner and middle magnetosphere and their coupling to the ionosphere. Generally, each of these models only include a subset of the relevant physics needed to describe the entire region. For example, some compute energy spectra, pitch-angle distributions, and charge-exchange rates for ring current particles (e.g., Jordanova et al., JGR, 111, A11S10, 2006). Some compute particle drifts self- consistently with electric and magnetic fields, including ionosphere-magnetosphere coupling (e.g., Lemon et al., GRL, 31, L21801, 2004). Global MHD models provide the overall magnetospheric context and some now include ion outflow (e.g., Glocer et al., JGR, 114, A05216, 2009) and coupling to active ionosphere-thermosphere models (e.g., Raeder et al., Space Sci. Rev., 141. 535. 2008). Much effort has been devoted to coupling these models together (e.g., DeZeeuw et al., JGR, A12219, 2004; Moore et al., JGR, 113, A06219, 2008). At this point, it would be easy to configure solar-wind-driven coupled models that could compute nearly all of the parameters to be measured in the GEMINI mission, including parameters measured by the GEMINI spacecraft themselves as well as ground observations and complementary spacecraft programs. Of course, the GEMINI images could help determine which model combination is most accurate. The broad central challenge for modeling now is to figure out how to adjust and upgrade the models to bring them into optimal agreement with observations made at many different points by many different instruments. The global images provided by GEMINI of the plasmasphere, ring current, and innermost plasma sheet will help enormously, because comparison with images will show how well the models are doing throughout a large region of the magnetosphere that is central to the most important magnetospheric events, including substorms and storms as well as sawtooth and steady-magnetospheric-convection events. Ultimately, models constrained by imaging data will lead to better predictive capabilities in which upstream solar wind conditions can be used to forecast conditions throughout the magnetosphere-ionosphere-thermosphere system. This will not be verified without the global scale constraints that a mission like GEMINI can provide. Evaluation Criteria High Priority: The basic mission design and science objectives for this GEMNI mission have appeared as specific missions and science concepts in the previous Solar and Space Physics Decadal Survey and the 1997 SEC Roadmap (as SMI), in the 2003 NASA Roadmap (as GSRI), and in both the 2005 and 2009 NASA Heliophysics Roadmaps (as GEMINI). Contribution to Multiple Panel Themes: GEMINI contributes both to the Solar Wind-Magnetosphere Interactions theme as well as to the Atmosphere-Ionosphere-Magnetosphere Interactions theme of the current Heliophysics Decadal Survey. Coupling and feedback between and within geospace regions (the atmosphere, ionosphere and magnetosphere and the solar wind) are fundamentally important in determining the response of the Earth’s near-space environment to the high-energy electrified plasmas and magnetic fields moving outward from the sun. The interplay between geospace components can alter the first order global system response even going so far as to limit the entry of solar wind energy during extreme events. Key science questions for the next decade center on this coupling. A true understanding of Earth’s near-space environment requires a new observational approach that provides a systems view of geospace and includes any effects of hemispheric asymmetries on the global response. Contributes to Important Scientific Questions: The GEMINI science objectives derive from the NASA Heliophysics Roadmap Societal Relevant Science Investigation: How do the magnetosphere and the ionosphere systems interact with each other? And the fundamental questions related to plasma processes that determine how energy and momentum from the solar wind propagate downward through geospace to Earth. Understanding the dominant plasma acceleration and transport processes operative in the Earth’s geospace region also has more general applicability. Particle acceleration and particle transport are two of the most fundamental processes in the plasma universe occurring in essentially every region of the heliosphere from the Sun to the heliopause, in the solar wind, in planetary magnetospheres and ionospheres, in cometary tails, and many others. The same processes that have been discovered by Heliophysics missions form a foundation for understanding astrophysical systems. Complements Other Observational Systems or Programs Available: As discussed above, GEMINI exquisitely complements a multitude of other observational systems, including everything from SDO to upstream solar and solar wind measurements to geosynchronous, GPS, and various LEO spacecraft (both NAS and other agency), as well as many ground based resources (radar, magnetometers, auroral imaging arrays). GEMINI science goals directly benefit from these other systems, and science based primarily on any of these systems is enhanced by what GEMINI can contribute. Is Affordable: Estimated Cost, FY2010 $290M to $405M including 25% reserve, all mission phases; For 10 year mission, cost is estimated $410M to $530M Appropriate Degree of Readiness: No technology developments required. Instrument TRL is high (5 to 9). Mapping to RFA, Decadal Challenges, and Decadal Missions This science target primarily falls under research focus areas H2 to understand changes in the Earth’s magnetosphere, ionosphere, and upper atmosphere to enable specification, prediction, and mitigation of their effects and F2 to understand the plasma processes that accelerate and transport particles. This science target is primarily relevant to Decadal Survey Challenges numbers 3, 4, and 5: Challenge 3: Understanding the space environments of Earth and other solar system bodies and their dynamical response to external and internal influences. Challenge 4: Understanding the basic physical principals manifest in processes observed in solar and space plasmas. Challenge 5: Developing a near real- time predictive capability for understanding and quantifying the impact on human activities of dynamical processes at the Sun, in the interplanetary medium, and in Earth’s magnetosphere and ionosphere.