A NASA probe will hurtle past Saturn's moon Enceladus on Wednesday, coming to within just 30 miles of the surface.
In the process, it will sample mist from a liquid ocean beneath the frozen surface. Doing so may provide clues about whether the ocean can support life.
At just 314 miles across, researchers originally expected Enceladus to be a tiny ball of solid ice. But thanks to NASA's Cassini probe, they now know it's somewhere really special.
"We're very confident there's a liquid ocean underneath Enceladus' crust," says Linda Spilker, a project scientist for Cassini, which has spent the past 11 years orbiting Saturn.
Cassini has previously sent back images of water literally spewing out of the moon's south pole. Now on its 21st visit to Enceladus, the spacecraft will get closer to the geysers than it ever has before. The spacecraft will streak through the icy mist at 19,000 miles per hour. The entire encounter will last under a minute.
The real goal here is to figure out whether the hidden ocean that feeds those geysers could support life. Cassini will look for hydrogen gas burbling out of hot vents on the ocean floor.
"By measuring the amount of hydrogen coming out, we think we can better understand the amount of energy available in this ocean, this potential habitat for life," Spilker says.
On Earth, there's definitely life in hydrothermal vents. Cassini won't be able to tell whether the same is true on Enceledus, but if there is, Spilker says, it's not much of a life. The alien beings would cling to their vents, in darkness, far beneath the icy surface.
"[They] wouldn't know about the sun that was up there," Spilker says. "Or anything else that's going on."
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