Free Astronomy Magazine September-October 2018

11 SEPTEMBER-OCTOBER 2018 PLANETOLOGY ! T his map shows the topography of the south polar region of Mars, in- cluding topography buried by thick de- posits of icy material. The map is a combination of subsurface elevation data acquired by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) aboard the ESA’s Mars Express orbiter and surface eleva- tion data acquired by the Mars Orbiter Laser Altimeter aboard NASA’s Mars Global Surveyor orbiter. The black line shows the boundary of the south polar layered deposits, an ice-rich geologic unit that was probed by MARSIS. Ele- vation values within the black outline, as measured by MARSIS, show the to- pography at the boundary between the layered deposits and the underly- ing material, an interface known as the ‘bed’ of the deposits. The elevation of the terrain is shown by colors, with purple and blue representing the low- est areas, and orange and red the highest. The total range of elevation shown is about 5 kilometres. The radar data reveal previously undetected fea- tures of topography of the bed, includ- ing depressions as deep as 1 kilometre shown in purple in the near-polar re- gion. The boundary of the layered de- posits was mapped by scientists from the U.S.G.S. The dark circle in the upper center is the area pole-ward of 87° south latitude, where MARSIS data cannot be collected. The map covers an area 1670 by 1800 kilometres. [NASA/JPL/ASI/ ESA/Univ. of Rome/ MOLA Science Team/USGS] life than a medium in which such organisms might exist. That final − and most interesting − question remains. Could this possible briny, subglacial lake support life? The general consensus is that the chances are very small. When scien- tists state that liquid water is a necessity for life, implicit in that statement is the fact that liquid water has enough energy to allow organic molecules to move and chem- istry to happen. A possibly -68°C salty brine is far removed from tropical sea water, al- lowing, at best, slow movement of dissolved molecules and only slow and infrequent chemistry. That said, Earth is full with ex- tremophiles that grow and thrive in envi- ronments that would quickly kill off other organisms − and 4 billion years is a long time to adapt to inhospitable conditions. Upcoming Mars missions will be directly probing the likelihood of existing or an- cient life on the planet, and astrobiologists anxiously await the findings. To have life develop independently on two or more bodies in our own Solar System would fun- damentally change our perceptions of life beyond our very small neighborhood in ways far more profound than how the dis- covery of exoplanets has changed our un- derstanding of planetary formation.