Icy Craters on Mars and Ceres

Abstract

The broad topic of my PhD dissertation is: Where and when do volatile compounds exist on the surface of planets? My two areas of focus are Mars and Ceres. For Mars, I study the Polar Layered Deposits (PLDs), which contain a stratigraphy that may contain a record of Mars climate history. In my thesis, I use crater statistics based on High Resolution Imaging Science Experiment (HiRISE) images to measure crater diameters on the North PLD (NPLD) and Context Camera (CTX) images for craters on the South PLD (SPLD), in order to determine the model ages of the surfaces. I utilize a new crater production function for Mars developed from real-time, direct observations of new craters forming on Mars today [Daubar et al., 2013]. I find that the NPLD surface age, using the new crater production function, is an order of magnitude younger than previously calculated, and that the expected accumulation rates within craters could be as high as ~cm/terrestrial year. For the South PLD, I large disparity in surface ages depending on which crater production function used. For Ceres, I model water ice sublimation as a source of the transient exosphere. The transient water vapor exosphere is not unexpected due to the high water content of Ceres determined from geophysical modeling, but the source is still unknown. I combine a thermal and vapor diffusion model in order to determine what possible sources of water ice (buried water ice tables or exposed surface ice) could explain the magnitude of this observation. I eliminate a water ice table, both massive and pore-filling, as the sole source of the present day telescopic detections. I find that currently exposed surface ice can, in some conditions, generate seasonally varying water vapor at the right order of magnitude of production to match telescopic observations. However, the water ice exposures currently identified on Ceres alone are not enough to match the telescopic vapor production rate. Small impacts over short timescales can provide a similar amount of vapor, but an ice table, the currently observed water ice patches, and ice-exposing impacts over short time scales still only produce at most ~16% of the vapor inferred by telescopic observations.