Phobos Surface Sputtering as Inferred From MAVEN Ion Observations

Abstract

AbstractPhobos 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.