Small meteoroids’ major contribution to Mercury’s exosphere

Abstract

The contribution of the meteoroid population to the generation of Mercury's exosphere is analyzed to determine which segment contributes most greatly to exospheric refilling via the process of meteoritic impact vaporization. For the meteoroid data, a differential mass distribution based on work by Grün et al. (Grün, E., Zook, H.A., Fechtig, H., Giese, R.H. [1985]. Icarus 62(2), 244–272) and a differential velocity distribution based on the work of Zook (Zook, H.A. [1975]. In: 6th Lunar Science Conference, vol. 2. Pergamon Press, Inc., Houston, TX, pp. 1653–1672) is used. These distributions are then evaluated using the method employed by Cintala (Cintala, M.J. [1992]. J. Geophys. Res. 97(E1), 947–974) to determine impact rates for selected mass and velocity segments of the meteoroid population. The amount of vapor created by a single meteor impact is determined by using the framework created by Berezhnoy and Klumov (Berezhnoy, A.A., Klumov, B.A. [2008] Icarus, 195(2), 511–522). By combining the impact rate of meteoroids with the amount of vapor a single such impact creates, we derive the total vapor production rate which that meteoroid mass segment contributes to the Herman exosphere. It is shown that meteoroids with a mass of 2.1 × 10−4 g release the largest amount of vapor into Mercury's exosphere. For meteoroids in the mass range of 10−18 g to 10 g, 90% of all the vapor produced is due to impacts by meteoroids in the mass range 4.2 × 10−7 g ≤ m ≤ 8.3 × 10−2 g.

A cold‐pole enhancement in Mercury's sodium exosphere

“…So far, we have discussed the recycling of sodium atoms between the top surface and exosphere but not the ultimate source of sodium. Before it reaches the surface or exosphere, the sodium is extracted from the regolith by a variety of poorly constrained processes that include thermal diffusion and ion-enhanced diffusion from regolith grain interiors [McGrath et al, 1986;Sprague et al, 1990;Killen and Morgan, 1993;Killen et al, 2004;Burger et al, 2010], impact vaporization [Cremonese et al, 2006;Berezhnoy and Klumov, 2008;Grotheer and Livi, 2014;Burger et al, 2014;Merkel et al, 2016], and ion sputtering [McGrath et al, 1986;Wurz et al, 2010;Pfleger et al, 2015].…”

Seasonal Variability of Mercury's Sodium Exosphere Deduced From MESSENGER Data and Numerical Simulation

“… R is the polar radial coordinate from the Sun. was estimated by using numerical calculations following Grotheer and Livi (2014). c Na is equal to the fraction of Na atoms in the regolith, unlike the case of SWS.…”