Two moons in the outer solar system—Jupiter’s Europa and Saturn’s Enceladus—are becoming the undisputed top targets in the search for life elsewhere in the solar system, scientists and NASA officials said at a press conference Thursday. Beneath their icy crusts both moons have deep, global oceans of liquid water, kept warm by tidal tugs from the gas-giant planets they orbit. Whether anything swims in those oceans remains unknown—but perhaps not for long.
At Enceladus, NASA’s Cassini spacecraft has discovered molecular hydrogen—a potential foodstuff for bacteria and a sign of hydrothermal activity—within plumes of water vapor venting from the ocean into space through cracks in the moon’s surface ice. At Europa, earthbound telescopes have spied signs of similar plumes, tracing one that seems to repeat—an “Old Faithful” of the outer solar system—to a mysterious thermal anomaly on the moon’s surface. Both findings boost the case for sending future life-finding missions to each moon as part of NASA’s burgeoning “Ocean Worlds” program of interplanetary exploration.
“These ‘ocean worlds’ have just been discovered,” said Jim Green, director of NASA's planetary science division. “They are in our solar system. We need to probe them because they are among the best locations—we believe—that may harbor life today.”
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