Other
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010eguga..1214555s&link_type=abstract
EGU General Assembly 2010, held 2-7 May, 2010 in Vienna, Austria, p.14555
Other
Scientific paper
The discovery measurements of Mercury's exospheric magnesium, obtained by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) probe during its second Mercury flyby, are modeled to constrain the source and loss processes for this neutral species. Fits to a Chamberlain exosphere reveal that at least two processes are required to reconcile the distribution of magnesium measured far from and near the planet: a hot ejection process at the equivalent temperature of several tens of thousands of degrees K, and a competing source at lower temperatures, 3000-5000 K. The cooler process is consistent with an impact vaporization source at an inferred rate of (3-7)x105 atoms cm-2 s-1. Models of ion sputtering indicate that this process may provide ~20% of the column abundance measured over the polar areas if a mean influx to the surface of 2x108 solar-wind protons cm-2 s-1 poleward of ±50° latitude and an effective sputter yield of 0.1 per ion are assumed. This result leads to the conclusion that another energetic process, such as the rapid photodissociation of exospheric MgO, assumed to be produced by meteoroid and micrometeoroid impacts at an inferred rate of (5-12)x105 molecules cm-2 s-1, is required in order to explain the residual distant neutral component. The total amount of impact-produced magnesium is found to be less than that predicted by impact vaporization models for any reasonable combination of magnesium abundance in the regolith, a result that, subject to uncertainties in the meteoroid influx, suggests that condensation during hypervelocity impacts might constitute a major loss process for gas-phase refractories.
Benna Mehdi
Bradley Eric Todd
Killen Rosemary
McClintock William
Sarantos Menelaos
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