How ARTEMIS Contributes to Key NLSI Objectives C.T. Russell, J. Halekas, V. Angelopoulos, et al. NLSI Lunar Science Conference Ames Research Center Monday, July 21,

THEMIS Extended Phase = THEMIS baseline + ARTEMIS ARTEMIS Lunar Exploration 2

THEMIS Prime Mission ( ) –Five spacecraft mission in Earth orbit to study magnetospheric dynamics THEMIS Extended Phase ( ) –Continues original THEMIS baseline (3 probes) –Pursues new objectives in lunar orbit (2 probes) ARTEMIS provides measurements: –From the Moon Earth’s magnetosphere Basic plasma physics –Of the Moon Interior structure –On the Moon Surface composition and weathering Exospheric composition, structure, and dynamics Electric fields and dust Support for other planetary missions (LRO, LADEE, etc.) THEMIS and ARTEMIS 3

ARTEMIS Payload SST ESA EFIa EFIs FGM SCM T spin =3s Probe instruments: ESA: ElectroStatic Analyzer (Carlson and McFadden) -Ions, Electrons ~3eV-30 keV SST: Solid State Telescopes (Larson) -Ions, Electrons > 25 keV FGM: FluxGate Mag. (Glassmeier, Auster, Baumjohann) -3-axis B measurements, 0.1 nT sensitivity SCM: SearchCoil Mag. (Roux) -B at frequencies 10Hz-4kHz EFI: Electric Field Instrument (Bonnell) -3-axis E fields: DC – 8kHz ESAFGMSSTEFISCM

ARTEMIS Orbit  6 Mo. Lissajous Transition Orbit:10-30 RL  17 Mo. Final Lunar Orbit  P1, P2 Periselene: 100 km, 1500 km  P1, P2 Aposelene: 10 RL LOI to 100 x 16,000 km 83.5 m/s LL2 Lissajous Orbits

In the Magnetosphere, study: – Particle acceleration – Reconnection: 3D character and global effects – Turbulence: Drivers and effects Reveal 3D distant tail, dynamics First two-point measurements; from gyroradius to R E scales In the Solar Wind, study: – Particle acceleration at shocks – Nature and extent of reconnection – Inertial range of turbulence First two-point measurements, at 1-10R E Plasma Physics from the Moon

Science from the Moon: Wake The Moon is an ideal plasma laboratory for studying magnetized plasmas. The simple geometry of the Moon and its absorbing boundary produces a system that can be readily modeled with computers. This allows the codes to be tested and the physics to be understood. ARTEMIS measurements are particularly useful for such tests. 7

Dust Levitation in Electric Fields Apollo observers saw dust elevated above the lunar surface to possibly high altitudes. LADEE will probably have a dust detector, but has no capability of measuring the solar wind electric and magnetic fields. ARTEMIS measures the solar wind velocity and the interplanetary magnetic field and hence the solar wind electric field. It also can measure surface potentials with electron reflectometry. ARTEMIS plus LADEE will enable us to determine the response of charged lunar dust to the lunar and solar wind electric fields. ARTEMIS-1 ARTEMIS-2 LADEE 8

Interior Structure of the Moon Apollo orbital measurements provided evidence of an iron core of about 400 km radius. Lunar Prospector made similar (single instrument) measurements and confirmed the Apollo subsatellite result. Two-point measurements are needed to go beyond the current two-layer model of the interior electrical conductivity. ARTEMIS will provide measurements of both the “exciting” field and the resulting induced magnetic field at about 100 km over a range of frequencies and sound the electrical conductivity profile above the core. Core? P2P1 9

Volatile Inventory and Lunar Outgassing Apollo’s ALSEP package contained a suprathermal ion detector (SIDE) that detected ions accelerated by the electric field toward the lunar surface. The temporal history of these ion fluxes suggested that the moon might be episodically outgassing. Alpha particle observations of localized concentrations of radon also support this viewpoint. This observation needs confirmation. If true, there may be a source of lunar volatiles at low latitudes, not just at the poles. ARTEMIS has an ion detector and measures the solar wind electric field so it can test the SIDE hypothesis of an outgassing moon. Exospheric Pickup Ion ARTEMIS-2 ARTEMIS-1 H+H+ He + H2O+H2O+ S+S+ V ,x Solar Wind 10

Human Activities: Effect on the Atmosphere The Moon is now the subject of rapidly increasing exploration: now robotic, soon human. These activities will alter the thin lunar atmosphere, changing its composition and density. We need to understand the present atmosphere, its sources and losses, before it is altered. This knowledge will help us to predict losses of the new gases introduced to the Moon. Artemis with its ion detector and magnetometer enables a “mass” spectroscopic study of the lunar atmosphere utilizing solar photons to ionize the neutral atmosphere. 11

In support of LRO: –ARTEMIS provides comprehensive monitoring of lunar space environment –Complements LRO/CRATER measurements below 200keV ARTEMIS and Support for other Planetary Missions In support of LADEE: –ARTEMIS provides comprehensive monitoring of plasma conditions and lunar surface electric fields –Allows study of the response of the lunar exosphere and dust to external drivers In support of all missions –ARTEMIS provides solar wind monitoring 12

Summary ARTEMIS consists of two well-instrumented spacecraft measuring the Moon’s plasma and magnetic environment. ARTEMIS can determine –How dust is levitated –The interior electrical conductivity of the Moon –Whether the Moon has significant outgassing episodes –The effect of the exploration program on the lunar exosphere –The fundamental physical processes at work in a magnetized plasma 13