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 CO 2 and H 2 O frost formation on Mars, and assess their distribution relative to gully landforms. CO 2 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 H 2 O frost, the global H 2 O frost point distribution generally follows water vapor column abundance, and is weakly correlated with surface pressure. Most global CO 2 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 CO 2 frost detections. We predict that the conditions necessary for significant present‐day gully activity include a few centimeters of CO 2 frost within loose, unconsolidated sediments (I ∼ 300 Jm − 2K − 1s − 0.5 ) on relatively steep (>20°) slopes. Additionally, it could be possible for small amounts of H 2 O 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.