Plenty of water in our Solar System


enceladus-moon-lifeThis week in the journal Nature, an international team of scientists reported evidence for hydrothermal vents on the Saturnian moon Enceladus, with temperatures of its rocky core surpassing, in some places, 194 degrees Fahrenheit (90 degrees Celsius). The discovery, if confirmed, would make Enceladus the only place other than Earth with this chemical reactions, what for many scientists, would make Enceladus a most promising place to look for life.

Meanwhile, in a paper published Thursday in The Journal of Geophysical Research: Space Physics, another team reported signs of another under-ice ocean, on Ganymede, the largest of Jupiter’s moons. Scientists already have the theory that there is a large ocean, also covered by ice, on another Jovian moon, Europa. NASA’s Galileo spacecraft had also found hints of hidden water on Ganymede and on another of Jupiter’s moons, Callisto.

The new research, using the Hubble Space Telescope, fits with the earlier hints. “This is now stronger evidence for an ocean,” said Joachim Saur, a professor of geophysics at the University of Cologne in Germany and the lead author of the Ganymede paper.“After spending so many years going after Mars, which is so dry and so bereft of organics and so just plain dead, it’s wonderful to go to the outer solar system and find water, water everywhere,” said Dr. McKay, who studies the possibility of life on alien worlds. The earlier evidence for an ocean on Ganymede came from magnetic measurements during flybys by the Galileo probe, which suggested a conductive layer below the surface. Ice is not a good conductor, saltwater is. But the readings could also be explained by oddities in Ganymede’s magnetic field.

In the new research, the Hubble telescope scrutinized Ganymede for seven hours. It could not see below the surface, but it observed the shimmering lights of Ganymede’s auroras. As Jupiter rotates, once every 10 hours, its changing magnetic field causes the auroras to sway. If Ganymede were frozen, computer simulations showed, its aurora would sway by 6 degrees. But the salts of an under-ice ocean would generate a counteracting magnetic field and the auroras would sway by only 2 degrees.

In spite of everything, as a place for life, Ganymede is less promising, because the ocean looks to be sandwiched between layers of ice and not in contact with rock, in contrast, Enceladus appears to possess all of the necessary ingredients — heat, liquid water and organic molecules — and a future probe could analyze the water by simply flying through the plumes.