Cassini samples an alien ocean
NASA/JPL-Caltech/Space Science Institute

Cassini samples an alien ocean

NASA’s Cassini spacecraft has just sent back the first pictures from its deep plunge toward the surface of icy Enceladus, a flyby that took it through one of the moon’s geysers. No visuals of the geyser itself yet—but the spacecraft’s new, unprocessed images of Saturn’s sixth largest moon highlight its fractured, cratered surface. Since Cassini began its flybys of Saturn and its moons in 2005, scientists have learned that beneath the layer of ice is a global ocean about 10 kilometers thick that may harbor life and probably contains hydrothermal vents. They have spotted more than 100 huge geysers of ice particles, water vapor, and organic molecules spewing from fractures in the ice covering Enceladus’s south polar region. These plumes shoot the contents of the moon’s subglacial ocean hundreds of kilometers high, in eruptions that may resemble curtains rather than columns. This week, the spacecraft made its deepest dive into one such plume—just 49 kilometers above the moon’s surface—to sample its contents. Scientists don’t expect that the spacecraft will detect life. However, by diving deeper it should give them a fuller picture of the plumes’ makeup, perhaps even settling the column-versus-curtain debate. And, of course, they want to know how hospitable that buried ocean is for biology. Molecular hydrogen in the plume, for example, would help confirm hydrothermal activity on the sea floor, a potentially important ingredient for life. But that data likely won’t be available for several months. For now, we can just admire the view.