Search for a high-altitude lunar dust exosphere using Clementine navigational star tracker measurements

During the 1994 Clementine lunar mapping mission, portions of 25 orbits were dedicated to a search for lunar horizon glow (LHG) using the spacecraft star tracker navigation cameras. Previous putative detections of LHG were believed to result from forward scattering of sunlight by exospheric dust gra...

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Bibliographic Details
Published in:Journal of geophysical research. Planets 2014-12, Vol.119 (12), p.2548-2567
Main Authors: Glenar, David A., Stubbs, Timothy J., Hahn, Joseph M., Wang, Yongli
Format: Article
Language:English
Subjects:
Abundance
Altitude
Atmosphere
Brightness
Cameras
Computer simulation
Dust
dust scattering
Estimates
Exosphere
Fluctuations
Forward scattering
Geophysics
Grains
High altitude
Limbs
Lunar dust
Lunar exosphere
Mapping
Moon
Navigation
Orbits
Scale height
Searching
Spacecraft
Spacecraft contamination
Star trackers
Stars
Stellar mass
Subtraction
Sun
Sunlight
Sunrise
Sunset
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Summary:During the 1994 Clementine lunar mapping mission, portions of 25 orbits were dedicated to a search for lunar horizon glow (LHG) using the spacecraft star tracker navigation cameras. Previous putative detections of LHG were believed to result from forward scattering of sunlight by exospheric dust grains with radii ≈ 0.1 µm, observable above the limb from within the shadow of the Moon near orbital sunrise or sunset. We have examined star tracker image sequences from five Clementine orbits in which the limb occulted the Sun, and was at least partially shadowed from earthshine, minimizing the chance of stray light contamination. No LHG appears in the image data, or in any of the net brightness images, after subtraction of a reference zodiacal light model. However, some of the images display faint excess limb brightness that appears to be solar streamer structure. Therefore, we derive upper limits for the amount of dust in the lunar exosphere that could be hidden by these brightness fluctuations using a dust‐scattering simulation code and simple exponential dust profiles defined by surface concentration n0 and scale height H. Simulations using grains of radius 0.1 µm show that fluctuations in the observed excess brightness can be matched by a dust exosphere with a vertical column abundance n0H of 5–30 cm−2 and overlying mass
ISSN:2169-9097
2169-9100
DOI:10.1002/2014JE004702