Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p51d..06g&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P51D-06
Astronomy and Astrophysics
Astronomy
6250 Moon (1221), 7849 Plasma Interactions With Dust And Aerosols (2461)
Scientific paper
During the Apollo missions, horizon glow (HG) was observed by astronauts in lunar orbit just prior to orbital sunrise. These observations were further supported by excess brightness which appeared along the horizon in coronal photographs from Apollo 15 and 17. Horizon glow may also be present in star tracker measurements acquired during the Clementine mission, though it would be heavily masked by coronal and zodiacal light (CZL). The most likely cause of HG is thought to be forward scattering of sunlight by submicron dust grains in the lunar exosphere above the terminator, extending to 10's of km or higher in altitude. Such a dust population is thought to arise from charged lunar dust that has been electrostatically lofted from the surface, since strong surface electric fields are believed to exist at the terminator. Additional contributions to exospheric dust will arise from meteoritic ejecta. With many missions now returning to the Moon, it is important to be able to distinguish and quantify the observable sources of UV-VIS optical emission, specifically HG from lunar exospheric dust, CZL, and line emission from exospheric gases. We have developed a code which simulates 3D (2D spatial plus spectral) intensities of horizon glow arising from lunar exospheric dust, as it would be viewed from an orbiter in lunar shadow. The dust vertical profile used is the semi-empirical model proposed by Murphy and Vondrak. Dust scattering properties as a function of grain size are computed using Mie Theory. The code also incorporates CZL intensities as formulated by Hahn et al., as well as Na D-line emission as observed by Potter and Morgan, in order to contrast these three emission sources near the limb via their distinct spatial distributions, spectral intensities and dependence on solar elongation angle. We include a simulation of lunar HG, as it might be observed by the UV/Vis spectrometer aboard the Lunar Atmosphere and Dust Environment Explorer (LADEE).
Glenar David A.
Stubbs Timothy J.
Vondrak Richard R.
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