Liquid water appears to be a fundamental requirement for life, which is why a recently published article reporting evidence of a 20-kilometer-wide lake located at the bottom of Mars’s south polar ice cap—1,500 meters below the icy surface—has stimulated considerable scientific interest. The article’s authors proposed that concentrated salts, which lower the freezing point of ice, could account for the lake’s presence, but the study did not consider the conditions needed to melt ice in this location or whether they are physically plausible.
Now Sori and Bramson have taken this step to better constrain the circumstances under which subglacial water could form on Mars today. Using a series of one-dimensional thermal models, the team evaluated whether several key parameters, including subsurface heat flow and the concentrations of different salts, could induce melting at the base of the south polar ice cap.
Their results indicate that no amount of salt would suffice to melt the basal ice under typical Martian conditions. Instead, the researchers calculate that a local source of heat with a flux of at least 72 milliwatts per square meter would be necessary to raise subsurface temperatures high enough to melt the ice.
The authors argue that a subsurface magma chamber is the most plausible local heat source. According to their calculations, a chamber with a diameter of at least 5 kilometers, located about 8 kilometers below the ice, and appearing within the last few hundred thousand years could generate enough heat to create a lake that is 20 kilometers wide. Because of the spotty nature of magmatism, this explanation implies that liquid water is not likely to be widespread along the ice cap’s base. Although the authors caution that the presence of this liquid water on Mars must still be confirmed, if it does exist, their findings imply that the Red Planet has experienced volcanism much more recently than other lines of evidence have indicated. (Geophysical Research Letters, https://doi.org/10.1029/2018GL080985, 2019)
—Terri Cook, Freelance Writer