Other
Scientific paper
Oct 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.2101s&link_type=abstract
American Astronomical Society, DPS meeting #42, #21.01; Bulletin of the American Astronomical Society, Vol. 42, p.985
Other
Scientific paper
Measurements by instruments on MESSENGER during the spacecraft's three Mercury flybys have led to discoveries of previously undetected neutral (Mg) and ionized (Ca+) species in Mercury's neutral and ionized exosphere and mapped these and previously known constituents (Na, Ca) on the anti-sunward side of the planet and over the poles. Also, Neutron Spectrometer measurements have indicated neutron absorption consistent with the presence of some combination of Fe, Ti, Sm, and Gd. Another element with a high neutron cross section is Mn. Manganese-bearing pyroxene has been inferred from modeling of Mercury Atmospheric and Surface Composition Spectrometer (MASCS) spectra of Mercury's surface. The total neutron cross section of Mn-bearing clinopyroxene, for example, (294.2 barns), is comparable to that of ilmenite (284.0 barns), and we suggest it as a possible neutron absorber at Mercury. Some ions and neutrals can be released directly from mineral surfaces by electron-stimulated desorption (ESD). Because cross sections of neutrals can be higher than photon-stimulated desorption (PSD) cross sections and because active electron precipitation on both the day and night side of Mercury can produce ESD of ions, at least part of the ionized exosphere is produced directly from surface materials by ESD. The process does not require photoionization of atoms or molecules. One inference is that model assumptions for ion production and magnetospheric- interactions may need to add ESD as another source. ESD experiments and simulations of electron precipitation on Mercury provide support for this suggestion. More laboratory work is required to quantify known, and to discover other, pathways to ion desorption from Mercury's surface. Searches for resonant fluorescent emissions from atoms, molecules and ions (e.g., Mn and S emission line triplets near 280 and 162 nm, respectively) in Mercury's neutral and ionized exosphere during the orbital phase of the MESSENGER mission are planned.
Boynton Willam V.
Grieves Gregory A.
Killen Rosemary Margaret
Lawrence D. Jr. J.
McClain J. L.
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