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| Titel |
Limits to Mercury's magnesium exosphere from MESSENGER second flyby observations |
| VerfasserIn |
Menelaos Sarantos, Rosemary Killen, William McClintock, E. Todd Bradley, Mehdi Benna, James Slavin, Sean Solomon |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250044508
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| Zusammenfassung |
| 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. |
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