Other
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.3803k&link_type=abstract
American Astronomical Society, DPS meeting #42, #38.03; Bulletin of the American Astronomical Society, Vol. 42, p.998
Other
Scientific paper
The Moon is known to have a surface-bounded exosphere, that is, a collision-free tenuous atmosphere. Although many ground-based observations have been conducted under different conditions of source candidates, continuous observations from the ground covering the whole lunar phase have been difficult because of strong reflected sunlight and geometrical constraints. Observations from a lunar orbiter, however, would be free of the constraints of ground-based observations. The present study presents the results of continuous observations of the sodium exosphere from the same lunar polar orbiter over a period of six months.
Observations of the lunar sodium exosphere were conducted from December 2008 through June 2009 using the UPI-TVIS (UPI: upper atmosphere and plasma imager; TVIS: telescope for visible light) instrument onboard the Japanese lunar orbiter SELENE (Kaguya). Variations in line-of-sight integrated intensity measured on the night-side hemisphere of the Moon could be described as a spherical symmetric distribution of the sodium exosphere with a temperature of 2400 to 6000 K. The average surface density in February is well above that in the other months, namely, by 30%. As for variation depending on lunar-phase angle, the sodium density gradually decreased by about 20% from the first to the last quarters during each lunar cycle, although any clear indication of changes in sodium density caused by the Moon's passages through the Earth's magnetotail could not be seen. One of the possible explanations for such a density decay in a half lunar cycle is an inhomogeneous source distribution of photon-stimulated desorption (PSD) on the lunar surface. If a sodium-rich region exists on the surface around λ = 90 ± 90 degrees, increased release of sodium atoms by PSD will explain the observed result.
Kagitani Masato
Kameda Shingo
Murakami G.
Okano Shinya
Taguchi Makoto
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