Enceladus, a tiny ice-ball of a moon orbiting Saturn, might not seem like a likely place for life. But when we sent NASA’s Cassini orbiter to do some investigating, we found that Enceladus was venting plumes of water 50 miles high. Those vapor jets also hold salt, ice and organic material, and gravity measurements suggest they are coming from an ocean lurking beneath the icy crust. Now researchers think that ocean might be heated by hydrothermal vents—maybe similar to ones on the bottom of Earth’s own oceans that enable life to flourish far from the Sun’s rays.
Two papers detail why scientists think Enceladus has these vents. The first, published in Nature, describe minute grains of silica found by Cassini’s cosmic dust analyzer floating in the space around Saturn. On Earth, the most common way to form such grains is near hydrothermal vents—the particles form when salty and slightly alkaline rich in dissolved silica undergoes a dramatic temperature drop, explains a statement from NASA. That drop causes the silica to precipitate into the minute grains. Enceladus’s geysers could then blast those grains into space.
"We methodically searched for alternate explanations for the nanosilica grains, but every new result pointed to a single, most likely origin," paper co-author Frank Postberg, a Cassini CDA team scientist at Heidelberg University in Germany, says in the statement.
The second paper, published in Geophysical Research Letters, looks for reasons why the plumes erupting from Enceladus are so rich in methane and also points toward hydrothermal activity as a likely source.
Where is this hydrothermal activity coming from? Saturn’s gravity itself "squeezes and stresses" the moon, writes Phil Plait for Slate’s Bad Astronomy blog. That wringing of the planet causes the cracks, or sulci, to form on Enceladus’s surface and builds up pressure to explain the jets of water vapor. It also tugs on the probable rocky core sitting at the moon’s center, warming it. Again, cracks can form where that core meets the ocean above—those are hydrothermal vents.
Temperatures at those vents reach at least 194 degrees Fahrenheit, the Nature paper researchers estimate. That makes the ocean a warm one.
While the evidence for these hydrothermal vents is still a bit scant, we might be on to something. Critics have pointed out that the silica grains weren’t gathered from the plumes themselves, just from near Saturn. However, "It's very hard to make silica in the Saturn system except if you have a warm wet environment," John Spencer, a researcher at the Southwest Research Institute in Boulder, Colo., told NPR. The best place to do it is on Enceladus.
Enceladus was already pinned as the most likely place to find life outside of Earth. This new information should make us even more excited.