Monitoring Active Gullies

Gullies are common on steep slopes of many impact craters on Mars. When gullies were first observed, there was a lot of excitement surrounding them because similar features form on Earth through the action of liquid water. However, liquid water is currently unstable on the surface of Mars. Long-term observations have prompted many scientists to question a liquid water origin for the gullies, and alternative ideas have been suggested. These include flows of salt-rich (briny) water, as the salt would allow water to be liquid under lower temperatures than those for pure water. Also "dry" processes, which do not require the action of liquid water at all. Monitoring of gullies by HiRISE could help scientists better understand the conditions where the gullies are active, and in doing so, help understand how they form. https://photojournal.jpl.nasa.gov/catalog/PIA23850