The Possible Contribution of Dielectric Breakdown to Space Weathering on Phobos

The origins of Phobos and Deimos are uncertain; both are so space weathered that their surface compositions are difficult to determine using spectral reflectance measurements. We show how the winter temperatures and associated conditions in the polar regions of Phobos could make the regolith susceptible to space weathering from dielectric breakdown caused by solar energetic particles (SEPs). During SEP events, charged particles accumulate throughout the top ~ 1 mm of the regolith, which has low condukctivity, and create subsurface electric fields that act to dissipate any net buildup of charge. The faster the net charge accumulates, the larger the electric field needed to dissipate it. If the magnitude of the subsurface electric field exceeds ~10 6 V m -1, then dielectric breadkown is likely. This process rapidly dissipates the buildup of charge by vaporizing electrically conducting channels through the regolith. Dielectric breakdown