SciTech

Food for microbes found on Saturn’s icy moon Enceladus

Saturn’s moon Enceladus contains molecular hydrogen, which many microbes use as food, scientists announced this month. And if microbe food is present on Enceladus, microscopic alien organisms could be too.

Enceladus, long thought to be a strong candidate for extraterrestrial life in our own solar system, has an icy crust with a vast ocean beneath. This ocean is heated by gravitational forces, and when it gets hot enough, the water forces through cracks in the ice and shoots into space — creating large plumes, like a geyser.

Scientists working on NASA’s Cassini mission wondered whether there was anything in these plumes besides water. On Oct. 28, 2015, the Cassini probe bypassed the moon’s south pole at less than half the speed it had in previous fly¬bys. The slow speed allowed Cassini to collect accurate data and samples from the plumes erupting out of the 80-mile-long parallel cracks in the ice known as Enceladus’s ‘tiger stripes.’

The plumes were almost entirely water, as the scientists had predicted, but they contained between 0.4 and 1.4 percent molecular hydrogen — a level “way above the limit for life,” according to NASA astrogeophysicist Chris McKay. “The ocean of Enceladus would be a nice place for life.” The plumes contained trace amounts of carbon dioxide, methane, and ammonia.

The exciting presence of hydrogen raised another question — where is it coming from? After consulting data from this and other missions, and ruling out the possibility that it was leftover material from the moon’s formation, scientists concluded that this much hydrogen could be produced only by extensive hydrothermal activity under Enceladus’s ocean.

“We are not saying Enceladus has life, but the discovery does move the moon higher on the list of potentially habitable places in the solar system,” says atmospheric scientist J. Hunter Waite. There is indeed such a list: Enceladus is just one of many moons in our solar system that might sustain alien microbes. Its neighbor, Saturn’s moon Titan, has an atmosphere and oceans of methane where methane-dependent life forms could flourish.