The Lunar Atmosphere and Dust Environment Explorer (LADEE): New Mission, Longstanding Questions

R. C. Elphic Project Scientist G. T. Delory Ed Grayzeck Deputy Project Program Scientist Hq Scientist P.P. R.R. MahaffyMahaffy A. Colaprete NASANASA GSFCGSFC NASA ARC

B. Hine M.M. HoranyiHoranyi NASA ARC CU/LASPCU/LASP

D. Boroson J. S. Salute MIT/LL NASA Hq LEAG Meeting 09-15-10 1 LADEE Context & Motivation

• 2003 NRC Decadal Survey: “New Frontiers in the Solar System: An Integrated Exploration Strategy” a. Make precise compositional measurements of the surface-bounded atmospheres of Mercury and the Moon and determine the relationship between ionospheres and magnetospheres, b. Quantify regolith processes on bodies with tenuous atmospheres. • Objective Sci-A-3 in the LEAG Roadmap (exosphere & dust) • National Research Council (NRC) report, “Scientific Context for the Exploration of the Moon” (SCEM)

LEAG Meeting 9-15-10 2 2 Exospheres, Dust and Comparative Planetology

Surface Boundary Exospheres (SBEs): Evidence of dust motion on most common type of atmosphere in asteroids and the Moon.... the solar system…?

Itokawa Moon

Europa & other Icy satellites

Io Large Eros Asteroids & KBOs

LEAG Meeting 9-15-10 3 3 Lunar Exosphere - Measurements

Lunar Atmospheric and Composition Experiment (LACE) 40Ar Measurements

Global model distribution of Ar-40 at 30 km and 50 km (provided by D. Hodges). Gas densities peak at the sunrise terminator, where desorption is greatest, > 4000/cc at 50 km.

LEAG Meeting 9-15-10 4 Lunar Exosphere – Emissions

• Na, K resonant scattering emission from sunlight.

LEAG Meeting 9-15-10 5 “Disappearing” Surficial H2O and OH

• Chandrayaan-1 M3, EPOXI and Cassini VIMS 3-m observations.

• Presence of H2 O and OH in/on surface grains: o Signature deepest at high latitudes and off-noon local times. o Where do OH, H2 O go? Into exosphere? Polar cold traps?

Pieters et al Science 2009 Clark et al Science 2009

LEAG Meeting 9-15-10 Lunar Exosphere Transport

LEAG Meeting 9-15-10 7 Dynamic Lunar Dust

• Surveyor 7 images of lunar horizon glow (“LHG”) • Prevailing theory: <10 um dust, ~150m away, ~1m high on sunset horizon

Lunar Ejecta and Meteorites experiment (LEAM) Terminators

100 m

• Apollo surface experiment LEAM detected dust activity correlated with the lunar terminators Berg et al., 1976

LEAG Meeting 9-15-10 8 Baseline Science-Instrument Traceability

LEVEL 1 LEVEL 2 LEVEL 3

4.2.1.1 Measure spatial and Neutral/ion mass spectra NMS temporal variations of Ar, 40Ar, He He, Na, and K. Temporal scales: 12 hours to 1 month. UV/visible spectra Resolve variations SNR > 5 for resonant emission UVS within±20 of the Na, K terminator. UV/visible spectra 4.2.1.2 Detect or establish new O, OH, H2 O, and Mg, Al, Si, Ca, Ti, UVS limits for selected species Fe at SDT density limits, w/SNR > 5 exogenic/volatiles (CH4, O, Neutral/ion mass spectra OH, H2 O, CO, S), endogenic CH , CO, H O, OH, S, and Fe, Al, (regolith-derived refractory) 4 2 NMS (Si, Al, Mg, Ca, Ti, Fe) Mg at SDT density limits

UV/visible spectra 4.2.1.3 Perform survey for other over passband UVS species … within mass range 2-150 Da, sensitivity of Neutral/ion mass spectra several particles/cc 2-150 Da with a sensitivity of several NMS particles/cc.

LEAG Meeting 9-15-10 Baseline Science-Instrument Traceability

LEVEL 1 LEVEL 2 LEVEL 3

4.2.1.4 Detect or set new limits for UV/visible spectra -4 spatial and size distribution Detect >100 nm grains n >10 /cc over 1.5 to 50 km altitude of atmospheric dust: UVS • Solar occultation observations altitude range from 3 km up • Limb sounding, scattered light to 50 km, with a height resolution of 3 km, minimum detectable density In situ spatial and size -4 of 10 grains/cc, 100 nm to distribution for dust grains < 1um LDEX at least 1 micrometer in Detect existence of dust >100 nm diameter. Temporal and Density 10-4/cc at 50 km spatial scales of 4.2.1.1.

NMS

4.2.1.5 Measurements over 100 day Operate instruments for 100 days UVS mission life in appropriate orbit

LDEX

LEAG Meeting 9-15-10 Science - 10 Instrument Payload

Neutral Mass Spectrometer (NMS) UV-Vis Spectrometer (UVS) MSL/SAM Heritage LCROSS heritage

In situ measurement of exospheric species

P. Mahaffy NASA GSFC Dust and exosphere measurements A. Colaprete 150 Dalton range/unit mass resolution NASA ARC

Lunar Dust EXperiment (LDEX) Lunar Laser Com Demo (LLCD) HEOS 2, Galileo, Ulysses and Cassini Heritage Technology demonstration SOMD - directed instrument SMD - Competed instrument High Data Rate 100 mm Optical Optical Comm Module M. Horányi, LASP D. Boroson MIT-LL ms de 51-622 Mbps Mo

l tro on ics C on ctr Ele

6 0 cm

LEAG Meeting 9-15-10 Orbit Design Tailored for Science

• Measurements at ≤ 50 km altitude over the sunrise terminator are of high priority

• Low altitude measurements desired throughout the orbit • Retrograde orbit (avoid sunlight into FOVs over sunrise terminator) • Orbit plane within ±20 of the equator (inclination 180 ± 20)

Near-circular Science Orbit 25 x 75 km

Aposelene

Periselene

LEAG Meeting 9-15-10 12 LADEE Payload & Schedule

UVS LADEE Milestones – LDEX Passed PDR: 7/20- 23/2010 KDP-C: Approved for Phase C, 8/23/2010 CDR: 5/18/2011 LLCD Launch Readiness Date: 5/02/2013

NMS

Ames Common Bus

LEAG Meeting 9-15-10 13 Summary

•• LADEELADEE missionmission addressesaddresses longstandinglongstanding questionsquestions outlinedoutlined byby thethe NRCNRC andand LEAG.LEAG.

•• PayloadPayload drawsdraws onon high-heritagehigh-heritage instruments.instruments.

•• LADEELADEE addressesaddresses aa keykey issueissue raisedraised byby LCROSS,LCROSS, LRO,LRO, Chandrayaan-1Chandrayaan-1 MM33,, EPOXIEPOXI andand CassiniCassini VIMSVIMS surficialsurficial HH22O/OH O/OH measurements:measurements:

–– originorigin andand transporttransport ofof volatilesvolatiles toto polarpolar coldcold traps.traps.

LEAG Meeting 9-15-10 14 End

LEAG Meeting 9-15-10 15 Model of Lunar Dust and Na Emissions

Stubbs et al., Planet. & Space Sci. 2010

July 20 – 23, 2010 16 LEAG Meeting 9-15-10 System Design Tailored to Meet Science Objectives (3) Meteor Shower Flux and LADEE Launch Date

Impact rate of ~5-cm objects

100 days ~9.5 events/hr globally

LADEE Launch

LEAG Meeting 9-15-10 Lunar Dust – in Orbit?

Gene Cernan sketches from Apollo McCoy and Criswell, 1974 Command Module

Apollo CM Trajectory

Dust?

• Eyewitness accounts of “streamers” from Apollo command module • Too bright to be meteoritic ejecta • Exosphere and/or high altitude (50 km) dust is one possibility • Key goal if LADEE is to help resolve this open question

LEAG Meeting 9-15-10 18 The Lunar Exosphere and Dust: Sources & Sinks

Inputs:Inputs: SolarSolar photonsphotons SolarSolar EnergeticEnergetic ParticlesParticles SolarSolar windwind MeteoricMeteoric influxinflux Dayside:Dayside: UV-drivenUV-driven LargeLarge impactsimpacts photoemission,photoemission, +10s+10s VV

Nightside:Nightside: electron-drivenelectron-driven negativenegative chargingcharging -1000s-1000s VV Processes:Processes: ImpactImpact vaporizationvaporization InteriorInterior outgassingoutgassing Chemical/thermalChemical/thermal releaserelease Photon-stimulatedPhoton-stimulated desorptiondesorption SputteringSputtering

LEAG Meeting 9-15-10 19