Free Astronomy Magazine November-December 2015

PLANETOLOGY source and, most likely, by the melting of ice masses. Unfortunately, however, the average Mars temperature at surface level is almost minus 63 degrees C, and only in rare circumstances it reaches and exceeds 0 degrees C. How is it possible then that in many places on Mars the water can move freely, even if for short distances? Already years ago, Oj- ha, McEwen and their assistants suggested that that water can present itself in a liq- uid state only thanks to a very high salinity level. And we are not talking about sodium chloride (cooking salt), that at most lowers the freezing point by a few degrees, but of less well-known com- pounds, which when dissolved in water can keep it liquid up to at least a few tens of degrees below zero, turning it into a kind of brine. In this spe- cific case, it was found that the RSL ap- pear when the environmental temperature reaches or exceeds minus 23 degrees C, and T hese two im- ages of the southwest wall of Asimov Crater show the trans- formations suf- fered by some RSL over a period of 2 Martian years. The black arrows indicate the points affected by major changes. [NASA/JPL, D.E. Stillman et al.]