講演情報
[PPS04-P19]Experiments on Water Ice Sublimation Under Simulated Planetary Conditions: Insights Into Pitted Terrain Formation On Mars, Ceres and Vesta
*Lauren Mc Keown1、Nagendra Dhakal1、Adrienne Dove1、Brady Dingmann1、Michael P Poston3、Jennifer E.C. Scully2、Hanna Sizemore4 (1.University of Central Florida、2.Jet Propulsion Laboratory、3.Southwest Research Institute、4.Planetary Science Institute)
キーワード：
Mars、Ceres、Vesta、Volatiles、Sublimation、Laboratory Experiments
Pitted terrains are polygonal to quasi-circular depressions that occur in clusters within impact craters across Mars, Ceres and Vesta. These features are proposed to be formed by either slow or rapid phase change of subsurface water. Individual pits range from 10 m to 3 km in diameter, increase in size with crater diameter and are hypothesized to reflect buried ice abundance at time of impact. Thus, pitted terrains can potentially be used as sounders for historic subsurface water ice abundance and depth. The two main schools of thought regarding pitted terrain formation are as follows: (1) low temperature and quiescent subsurface sublimation of ice-rich impact slurry [Hartmann et al., 2010] which suggests that pits represent void spaces, and (2) The Boyce Model [Boyce et al., 2012] which was used to account for the formation of Martian pitted terrain [Tornabene et al., 2012] and later applied to Vesta [Denevi et al., 2012] and Ceres [Sizemore et al., 2017], involving the explosive erosive action of gas `pipes’ formed by rapid degassing at high temperatures (>750°C). However, since that time, an advent of empirical studies of volatile phase change dynamics in regolith under vacuum resulted in a paradigm shift in our understanding of the agency of sublimation under low pressure and temperature. Volatile sublimation (albeit CO2) out of regolith has shown that vigorous sublimation dynamics can form a variety of pits under colder temperature regimes than those modeled by Boyce [Mc Keown et al., 2017, 2024). We present experiments performed under low temperature vacuum conditions in the UCF Microgravity Laboratory R2D2 chamber to investigate the parameter space bounded by these end-member models for water ice within regolith simulant. By heating a variety of buried water ice simulants within planetary regolith simulant, we constrain the relationship between volume and rate of water ice sublimated and morphology of pits. Acknowledging scale differences, we combine these observations with analysis of remote sensing imagery of pitted terrains to constrain the conditions where either rapid degassing or slow sublimation of water ice may have formed these features.