Measuring Mars Atmospheric Winds from Orbit
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Scott D Guzewich↗
Engineering topics
X Sun
Publications and source records attributed to X Sun.
Searching for Lunar Horizon Glow With the Lunar Orbiter Laser Altimeter
We present the results of a 2-year-long systematic campaign to monitor the lunar dust exosphere for enhancements in dust concentration at altitudes < 20 km both during and outside of major meteor stream periods. We utilize the radiometric capabilities of the Lunar Orbiter Laser Altimeter Laser Ranging telescope onboard the Lunar Reconnaissance Orbiter to search for forward-scattered sunlight from exospheric dust grains, called lunar horizon glow (LHG). Specifically, we test the hypothesis that major meteor streams can produce LHG similar to what was measured in Apollo 15 coronal photography. Assuming a one-dimensional exponential vertical dust profile and a dust grain radius r ~ 0:1 μm, we derive an upper limit of ~ 10(exp -11) g cm(exp -2) on the overlying column dust mass density near the terminator during stream periods, a limit roughly 10 times lower than inferred from Apollo 15. Recent studies at altitudes ~ 1 - 20 km outside of major meteor streams and at higher altitudes during streams placed limits on the density of similarly-sized grains ~ 100 - 1000 times lower than Apollo 15. Our results show that Apollo 15-like LHG, if real, is also a rare occurrence at altitudes < 20 km during major meteor stream periods. This study is the first to quantitatively constrain the role of meteor streams in producing Apollo 15-like LHG at altitudes < 20 km and small forward scattering angles, and further narrows the properties of any similar high-altitude LHG and the conditions under which it can occur.
M K Barker↗
Salty Bennu: Halite and Sylvite in Fines Returned by OSIRIS-REx
Salt phases such as halite (NaCl) and sylvite (KCl) are important hosts of halogens (e.g., Br and I) and volatile alkali metals (i.e., Na, K) and are very rare in extra-terrestrial materials. Halite and sylvite have been discovered in carbonaceous chondrite clasts in ordinary chondrite meteorite falls Zag H3-6 regolith breccia (Zag), Monahans (1998) breccia (Monahans), and Sidi El Habib H5 chondrite, as well as on the surface of particles from asteroid Itokawa. Yet, it is uncertain whether the evaporites are indigenous or exogenous to their respective parent bodies, and their origin is debated. Analysis of the extinct 129I/129Xe decay system and 40Ar/39Ar show that halite in Zag may have formed within the first 8 Myr of the solar system, possibly from aqueous fluids during local and episodic low-temperature alteration on the parent body. Halite and sylvite in Zag are characterized by light δ37Cl values of −1.7 ‰. Halite in Zag could have been transported from the outer solar system, perhaps a P- or D-class asteroid, as indicated by O, H, N, and C isotopes. An alternative is a cometary or interstellar ice origin due to their deuterium-rich and 16O-poor composition.
N E Timms↗