Researchers Think There's A Warm Ocean On Enceladus | KUOW News and Information

Researchers Think There's A Warm Ocean On Enceladus

Mar 12, 2015
Originally published on March 31, 2015 5:07 pm

Saturn's moon Enceladus is a mystery. From Earth it looks tiny and cold, and yet it's not a dead hunk of rock. Passing spacecraft see trenches and ridges, similar to Earth's, and in 2005 NASA's Cassini mission spotted ice geysers streaming from its south pole.

"The moon is actually alive in a sense," says Sean Hsu with the Laboratory for Atmospheric and Space Physics at the University of Colorado at Boulder.

Beneath the surface, most researchers believe it even has a liquid ocean. Now Hsu and his colleagues have found new evidence that it's a downright balmy ocean.

The team used the Cassini spacecraft, which orbits Saturn, to detect tiny particles of silica floating in space. It's not sand exactly, but researchers think the particles did come from the bottom of Enceladus' ocean.

The silica particles could only be made if that ocean were hot. "We think that the temperature at least in some part of the ocean must be higher than 190 degrees Fahrenheit," Hsu says. "If you could swim a little bit further from the really hot part then it could be comfy."

In fact, 190°F is cooler than many hydrothermal vents at the bottom of Earth's oceans. Hsu says experiments on Earth also suggest the ocean is similar in salinity and pH to oceans here.

The evidence, published in the journal Nature, is somewhat circumstantial. The theory is that the silica formed and then dissolved in seawater beneath Enceladus' icy crust. It then left the moon through geysers, and filled Saturn's E-ring. From the E-ring, the silica eventually wound up in the giant planet's magnetosphere, which is where Cassini saw it.

"It's not like they flew through the plumes of Enceladus and measured these particles," says Bill McKinnon, a planetary scientist at Washington University in St. Louis.

Nevertheless, he and other independent researchers think the hypothesis has a reasonable chance of being right. "It's very hard to make silica in the Saturn system except if you have a warm wet environment," says John Spencer, a researcher at the Southwest Research Institute in Boulder, Colo. Enceladus is the most likely place.

Why is tiny Enceladus so warm? Spencer suspects it's the gravitational pull of Saturn and some of its other moons. Their attraction could tug the water and rock inside Enceladus, causing it to slosh around and heat up.

But current models show that gravity alone can't explain the warm oceans, says McKinnon. He thinks something else could be generating that energy.

"The most exciting possibility is that there's ongoing chemical reactions between the rock inside Enceladus and the water," McKinnon says.

Those chemical reactions could generate heat, and possibly create conditions for life. Some primitive organisms on our planet live off energy from ocean vents on earth without ever seeing the sun. The energy heating Enceladus' oceans "could be exploited by simple living systems, as happens on the Earth," McKinnon says.

Right now, such speculation is still pretty far-fetched, but more clues are coming. Later this year, the Cassini spacecraft will skim past Enceladus at a distance of just 30 miles. It should provide one of the best opportunities yet to learn about what's going on inside.

Copyright 2015 NPR. To see more, visit http://www.npr.org/.

Transcript

STEVE INSKEEP, HOST:

Now let's drill down to understand a far more distant ocean. It's an ocean beyond the reaches of planet Earth. To find it, you would have to head for the planet Saturn and then find one of its many moons, a hunk of matter called Enceladus. That moon is covered by a thick layer of ice. New research suggests there's a balmy ocean beneath that cold surface. NPR's Geoff Brumfiel reports.

GEOFF BRUMFIEL, BYLINE: Enceladus is a mystery. From Earth, it looks tiny and cold. And yet, it's not a dead rock. Passing spacecrafts see trenches and ridges like here on Earth. In 2005, NASA's Cassini mission spotted ice geysers streaming from its south pole. Sean Hsu is at the University of Colorado.

SEAN HSU: The moon is actually alive in a sense.

BRUMFIEL: Beneath the surface, most researchers believe it even has a liquid ocean. Now Hsu and his colleagues have found new evidence for what this ocean is like. The team used the Cassini spacecraft to detect tiny particles of silica floating in space. The silica's not exactly sand, but researchers think it did come from the bottom of Enceladus's ocean. And it could only be made if that ocean was hot.

HSU: We think the temperature, at least at some part of the ocean, must be higher than 190 degrees Fahrenheit.

BRUMFIEL: That doesn't really sound like swimming temperatures.

HSU: No, but if you can swim a little bit further from the really hot part, it could be comfy.

BRUMFIEL: In fact, 190 degrees is cooler than many hydrothermal vents at the bottom of Earth's oceans. The evidence, published in the journal Nature, is a little circumstantial. But if it's right, then something is keeping the core of this ice world toasty warm.

BILL MCKINNON: The interesting thing to me is, like, you know, what is the source of the heat?

BRUMFIEL: Bill McKinnon is a planetary scientist at Washington University in St. Louis. There are many theories as to why Enceladus is so hot.

MCKINNON: The most exciting possibility is that there's ongoing chemical reactions between the rock inside Enceladus and the water.

BRUMFIEL: Those chemical reactions could be generating heat. But what's more...

MCKINNON: This is energy that can be exploited by simple living systems, as happens on the earth.

BRUMFIEL: Some primitive organisms on our planet live off energy from ocean vents. They don't need the sun. Could similar life exist under the ice of Enceladus? That's probably a bit of a long shot. But more clues are coming. Later this year, the Cassini spacecraft will skim past Enceladus at a distance of just 30 miles. It should provide one of the best opportunities yet to learn about what's going on inside this strange little moon. Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.