1 ARTEMIS and LADEE
The ARTEMIS mission is in a unique position to support the Lunar Atmosphere and Dust
Environment Explorer (LADEE) mission currently under development, by measuring both
upstream solar wind and local plasma conditions near the Moon. LADEE carries instrumentation
to study the dynamics of the lunar exosphere and dust environment, much of which will be tied
directly to the ambient plasma conditions at the Moon and in the solar wind. Sputtering by the
solar wind has been proposed as a leading mechanism for the generation of neutral exospheric
species such as Na [Potter & Morgan, 1994], along with photon-stimulated desorption (PSD) and
micrometeorite impacts [Mendillo et al., 1999]. Distinct changes in the exosphere have been
observed when the Moon enters the magnetotail [Potter et al., 2000; Wilson et al., 2006],
indicating the importance of the local plasma environment on exosphere dynamics. Most
recently, correlations between Lunar Prospector plasma data and ground-based observations
indicate that ion impact may enhance PSD efficiency [Sarantos et al., 2008], possibly due to the
introduction of crystal lattice defects in the regolith. This recent discovery is a preview of the
synergies possible between ARTEMIS and LADEE, in which one spacecraft measures the
complete plasma inputs to the system, while a second monitors the exospheric response. Since
LADEE lacks any plasma instrumentation, the presence of ARTEMIS will enable a clearer
linkage to specific physical processes causing exospheric variability measured by LADEE.
Similarly, ARTEMIS plasma measurements will shed light on the processes causing any dust
activity measured by LADEE. To first order, LADEE measurements may reveal some of the
more obvious potential sources of lofted dust, such as the terminator region where the surface
potential of the Moon is known to change on a regular basis [Farrell et al., 2008; Halekas et al.,
2005; Manka, 1973; Stubbs et al., 2006]. However, it is also possible that dust activity is rare on
the Moon, occurring only during extreme charging events [Halekas et al., 2007] or follows
unexpected temporal or spatial patterns. In this case ARTEMIS measurements of the plasma
conditions and surface potential could revolutionize our understanding of the underlying physical
mechanisms at work which would have otherwise gone unnoticed.
The LADEE launch is planned in late 2011 or early 2012, and thus will overlap with the nominal
ARTEMIS mission during its low-altitude phase (100 km? 500 km?) about the Moon. The
LADEE deputy project scientist is also an ARTEMIS Co-I, ensuring early and effective
scientific and operational coordination between these two missions prior to their conjunctions at
the Moon.
Farrell, W. M., T. J. Stubbs, J. S. Halekas, G. T. Delory, M. R. Collier, R. R. Vondrak, and R. P.
Lin (2008), Loss of solar wind plasma neutrality and affect on surface potentials near the lunar
terminator and shadowed polar regions, Geophys. Res. Lett., 35(5), 1-5
Halekas, J. S., G. T. Delory, D. A. Brain, R. P. Lin, M. O. Fillingim, C. O. Lee, R. A. Mewaldt,
T. J. Stubbs, W. M. Farrell, and M. K. Hudson (2007), Extreme lunar surface charging during
solar energetic particle events, Geophys. Res. Lett., 34, 02111
Halekas, J. S., R. P. Lin, and D. L. Mitchell (2005), Large negative lunar surface potentials in
sunlight and shadow, Geophys. Res. Lett., 32, 09102
Manka, R. H. (1973), Plasma and potential at the lunar surface, in Photon and Particle
Interactions with Surfaces in Space, edited by R. J. L. Grard and D. Reidel, pp. 347-361,
Springer, Dordrecht, Netherlands.
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Mendillo, M., J. Baumgardner, and J. Wilson (1999), Observational Test for the Solar Wind
Sputtering Origin of the Moon's Extended Sodium Atmosphere, Icarus, 137(1), 13-23
Potter, A. E., R. M. Killen, and T. H. Morgan (2000), Variation of lunar sodium during passage
of the Moon through the Earth's magnetotail, J. Geophys. Res., 105, 15073-15084
Potter, A. E., and T. H. Morgan (1994), Variation of Lunar Sodium Emission Intensity with
Phase Angle, Geophys. Res. Lett., 21
Sarantos, M., R. M. Killen, A. S. Sharma, and J. A. Slavin (2008), Influence of plasma ions on
source rates for the lunar exosphere during passage through the Earth's magnetosphere, Geophys.
Res. Lett., 35
Stubbs, T. J., R. R. Vondrak, and W. M. Farrell (2006), A dynamic fountain model for lunar
dust, Adv. Space Res., 37(1), 59-66
Wilson, J. K., M. Mendillo, and H. E. Spence (2006), Magnetospheric influence on the Moon's
exosphere, J. Geophys. Res., 111
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