Free Astronomy Magazine July-August 2018

ASTROBIOLOGY 25 T oday, Mars is an inhospitable planet, but over 3 bil- lion years ago it was much more similar to the con- ditions of our ancient Earth − the same conditions in which life here first developed. If, in those distant times, the martian surface had contained the necessary ingredients for life as we know it, then life would prob- ably have appeared there as well. The most basic of those ingredients are water, energy, and more-or-less complex organic molecules, which in their structure can JULY-AUGUST 2018 include carbon, hydrogen, oxygen, nitrogen, phospho- rus, sulfur and other elements. Water certainly existed on Mars in the first billion years of the solar system. The energy of the Sun never failed and, in ancient times, even geothermal energy could have supplied the heat necessary to support any possible elementary form of martian life. So far, however, we have not had the cer- tainty (beyond some controversial data) of the simulta- neous presence of organic compounds. But now, an T his low-angle self-portrait of NASA’s Curiosity Mars rover shows the vehicle at the site from which it reached down to drill into a rock target called “Buckskin” on lower Mount Sharp. [NASA/JPL-Caltech/MSSS]