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- Title
Phobos Surface Sputtering as Inferred From MAVEN Ion Observations.
- Authors
Nénon, Q.; Poppe, A. R.; Rahmati, A.; Lee, C. O.; McFadden, J. P.; Fowler, C. M.
- Abstract
Phobos is bombarded by both protons and alpha particles from the solar wind and by Martian atomic and molecular oxygen ions. A numerical model of the distribution of planetary ions has previously proposed that these ions may dominate solar wind ions in sputtering the surface of Phobos when the moon is located downstream of Mars. This conclusion suggests a unique link between planetary atmospheric escape at Mars and the surface processing of its moon yet, remains to be confirmed with in situ ion measurements. In this article, a 4‐year‐long average of the ion environment that Phobos is exposed to is constructed from in situ ion observations conducted by the Mars Atmosphere and Volatile Evolution (MAVEN) mission. In turn, the flux of material sputtered from the surface of Phobos by this environment is computed. We confirm that planetary atomic oxygen ions dominate over solar wind ions in sputtering the surface of Phobos downstream of Mars during 20% of the moon's orbit. We also reveal that molecular oxygen ions sputter the surface of Phobos as much as or more than atomic oxygen ions in the Martian magnetotail. In addition to the long‐term average picture, the time variation of Phobos surface sputtered fluxes is investigated during the series of solar wind events that hit the Martian system in March 2015. We find that the flux of material liberated from Phobos' surface increased by a factor of 50 during this period. Plain Language Summary: Phobos is the closest of the two moons of Mars and its surface is bombarded by positively charged particles, ions, that liberate surface material into space (sputtering). The moons of Mars are exposed to not only ions coming from the solar wind but also to ions coming directly from the atmosphere of their host planet. Previous work used a numerical model to study the relative importance of solar wind and Martian ions in sputtering the surface of Phobos and found that ions coming from Mars may be important, in particular when Phobos is behind Mars with respect to the Sun. However, this has never been discussed or studied with in situ measurements of ions. In this article, we use observations of ions obtained by the NASA Mars Atmosphere and Volatile Evolution mission (MAVEN), in orbit around Mars since 2014, to confirm that ions coming from Mars dominate solar wind ions in sputtering the surface of Phobos in the nightside. We also find that the flux of material liberated from the moon surface can increase by a factor of 50 during solar wind events. Key Points: The long‐term average ion environment at Phobos is constrained from 4 years of in situ measurementsPlanetary atomic and molecular oxygen ions dominate solar wind ions in sputtering the surface of Phobos downstream of MarsThe flux of material sputtered from the surface of Phobos increased by a factor of 50 during the March 2015 solar wind events
- Subjects
MARS Atmosphere &; Volatile Evolution (Artificial satellite); OBSERVATIONS of Mars; SOLAR wind; SOLAR activity; MARS (Planet); PHOBOS (Satellite)
- Publication
Journal of Geophysical Research. Planets, 2019, Vol 124, Issue 12, p3385
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2019JE006197