The Distribution of Frosts on Mars: Links to Present-Day Gully Activity

Numerous types of activity in mid latitude martian gullies have been observed over the last decade. Some activity has been constrained to occur in the coldest times of year, suggesting that surficial frosts that form seasonally and diurnally might play a key role in this activity. Here we use thermal infrared data to explore the global, spatial and temporal variation of temperatures conducive to CO₂ and H₂O frost formation on Mars, and assess their distribution relative to gully landforms. CO₂ frost detections are observed at all latitudes and are strongly correlated with dusty, low thermal inertia regions near the equator. While it is difficult to accurately detect the formation of H₂O frost, the global H₂O frost point distribution generally follows water vapor column abundance, and is weakly correlated with surface pressure. Most global CO₂ frost detections do not contain gullies, but 47% of all gullies, and 73% of active gullies (76% in the south, and 25% in the north) do overlap with CO₂ frost detections. We predict that the conditions necessary for significant present-day gully activity include a few centimeters of CO₂ frost within loose, unconsolidated sediments (I ∼ 300 (Formula presented.)) on relatively steep (>20°) slopes. Additionally, it could be possible for small amounts of H₂O frosts to play a role in present-day equatorial mass wasting events. However, whether present-day gully activity is representative of gully formation is still open to debate, because it seems unlikely that frosts can erode channels into rocky substrates–even considering geologic timescales.