Free Astronomy Magazine May-June 2015

22 PLANETOLOGY Those who thought that the richest salt water reservoirs belonged to the Earth should think again, as it is now cer- tain that on Ganymede, the largest natural satellite in our solar system, there is a subterranean ocean whose volume exceeds that of all our oceans put together. An extraordi- nary piece of news from the astrobiological point of view. The largest ocean is on Ganymede MAY-JUNE 2015 G anymede pho- tographed by the Galileo probe in 1996. This moon hosts below its surface the largest ocean in the solar system. [NASA, Ted Styrk]