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An image of Saturn's moon, Enceladus

An ocean detected on Saturn's moon Enceladus (above) lies between ice and rock about 25 to 30 miles (40 to 48 kilometers) below the surface.

IMAGE COURTESY NASA/JPL/SPACE SCIENCE INSTITUTE

Marc Kaufman

for National Geographic

Published April 3, 2014

A substantial ocean most likely exists beneath the icy surface of Saturn's diminutive moon Enceladus, raising the possibility that primitive forms of extraterrestrial life exist in its briny depths.

The ocean lies between the moon's rocky core and a layer of thick ice, and is estimated to be about the size of Lake Superior. That's large for a moon that is only 310 miles (500 kilometers) in diameter and could fit within the borders of Arizona.

In our solar system, the only other moon known to have similar contact between liquid water and rock is Jupiter's Europa. Both the rock and the water are considered to be essential for the chemistry that could, over eons, turn nonliving matter into living entities.

"The main implication of our work is that there are potentially habitable environments in our solar system that are entirely unexpected," said Luciano Iess, an aerospace engineer at the Sapienza University of Rome and lead author on the study published Thursday in the journal Science.

The surface temperature on Enceladus is -180 degrees Celsius (-292 degrees Fahrenheit), but enough heat is produced by tidal forces that flex and melt the ice to create liquid water below. That the ice is heated by the effects of Saturn's gravity—the source of those tidal forces—rather than by radiation from the sun, Iess said, reinforces the theory that even distant and frigid celestial bodies might be habitable.

"This strong indication of a regional sea under the ice on Enceladus heightens our interest in Enceladus as a possible habitable world," said Carl Pilcher, former director of NASA's Astrobiology Institute.

Mapping a Moon With Gravity

Scientists were surprised in 2005 when images taken by the Cassini-Huygens mission revealed substantial jets of salty water were spitting out from the south pole of Enceladus. Later, close flybys produced dramatic photos of the geysers and the additional discovery of carbon-based, organic compounds being released from nearby darkened fissures called "tiger stripes."

Those discoveries strongly suggested there was water below the surface, but imagery alone could not confirm the liquid's presence. The scientists had to use the Cassini spacecraft in a different way, in effect turning it into a divining rod. (See "Ten Best Pictures From NASA's Cassini Probe—Saturn, More.")

During three flybys Cassini made of Enceladus between 2010 and 2012, scientists studied the moon's gravitational field in detail by measuring ever-so-slight shifts in the satellite's path. The gravitational field of a moon or planet subtly varies due to changes in the density and amount of land or liquid across its surface. The changes in that field can affect a spacecraft orbiting above.

Cassini scientists used Earth-based radio telescopes from the Deep Space Network to measure those tiny gravity-induced changes in the satellite's path, and to then indirectly map facets of the moon below.

Comparing those gravity measurements with the moon's topography allowed researchers to conclude that large amounts of liquid water were present well below the surface. Key to the research is the fact that liquid water is 7 percent more dense than ice, which means it produces a greater gravitational effect.

"To get our data, we had to detect exquisitely small changes in motion with a pretty impressive precision," said co-author David Stevenson, a planetary scientist at the California Institute of Technology in Pasadena. "That was new, but the rest of the story of how to understand masses from our data is basically Newton's laws of motion."

Stevenson said that while the team's understanding of the water on Enceladus remained "somewhat fuzzy," members were quite confident that a reservoir had been found about 25 to 30 miles (40 to 48 kilometers) below the surface. The ocean, or sea, is estimated to be in a layer about 6 miles (10 kilometers) from top to bottom, lying between ice and rock.

The team was convinced that the water was present in the south polar region—where the geysers and tiger stripes are found. However, there was not enough data to determine whether it might spread farther around the globe, Stevenson said. The ocean under the surface ice of Europa, a much larger moon, has been determined to circle its globe.

Good Place to Look for Life

Although the gravitational data painted only a very rough picture of the composition of Enceladus, the findings go a long way toward explaining some of the surprising features of the tiny and frigid moon.

In a teleconference Wednesday, several members of the team said it was increasingly plausible that the water vapor in Enceladus's geysers is coming from the subsurface ocean and up through what Stevenson called the moon's "plumbing," to the tiger stripe region on the surface.

Jonathan Lunine, a planetary scientist and astrobiologist at Cornell University in Ithaca, New York, and another member of the Cassini team, said the organic material detected earlier in the plume and around the tiger stripes increases the possibility that some form of life exists, or once existed, on Enceladus.

So too does the new finding that the moon's ocean sits on bedrock. "Like at the bottom of our oceans, liquid water would seep through the rock and pick up nutrients and get warmer," Lunine said. "This makes the interior of Enceladus an attractive potential place to look for life."

Finding that life, though, wouldn't be possible with Cassini. The spacecraft's spectrometer initially detected the organic material on the moon. However, Lunine said, a far more powerful instrument would be needed to determine if complex organics and possibly life existed in the liquid water.

Cassini has been in orbit around Saturn since 2004 and is expected to pass by Enceladus three more times before the planned end of its mission in 2017. The Cassini team hopes to navigate the spacecraft through the geyser plume during one of the flybys to get an intimate look at its composition.

"More studies of the plume material, particularly a sample return," said Pilcher, "would help us understand if life might even exist on this small moon."

48 comments
Jeff Beilfuss
Jeff Beilfuss

There has always been a lot of wishful thinking about other life in the universe. Is there or isn't there other life? Saying there has to be other life doesn't make it true. The evidence is accumulating? It is too early to get excited. Suppose this planet is all there is? Now there's a thought to dampen the excitement. As far as we know, Earth is very unique until we find another one. Has anyone read anything about Martian soil having any organic matter capable of growing food for explorers? It takes more than water to survive. Even after the moon landings and the return with lunar soil we did not see any headlines about it being able to grow food.

Moacyr Pereira Passos Junior
Moacyr Pereira Passos Junior

Anyone new, cause water is primordial for life, thas we know..., and in the Universe, water exist..

But, no water, its is matter...

I live in São Paulo city, Brasil, and, at now, we are suffering fault of water, no rain, wather changing is stop the rain in  our region.... and reservatories are staying empty...

Save Enceladus....

Joyce Oliveras
Joyce Oliveras

I hope there are extraterrestrial marine sea creatures!!!!!! 

Richard Elkhal
Richard Elkhal

If we could live on another planet without a problem, I'm going.

p. benjamin
p. benjamin

Nice I hope there is life like maybe in europa

Terry Allitt
Terry Allitt

Another possibility for life in our solar system ! The solar system gets more and more fascinating :)

Hasan Kabir
Hasan Kabir

Love to learn more about Cassini's research! And what news of Titan?

Ste Schlappi
Ste Schlappi

Why are all of the craters concentrated in one general area?

M. Akhtar
M. Akhtar

Amazing, it is 1.2 billion km far from us, this water is useless for us. We have to think something else because we have only 2% drinking with us now.

Rodmy Montero
Rodmy Montero

Dwayne,

I guess is all salt water.

In order to produce fresh water is need the atmospheric cycles which allow the particles to evaporate, liquefy and run fresh.

Well unless water have special filtering conditions in which water would not mix then you would have your water fresh.

Just my guess.

Dwayne LaGrou
Dwayne LaGrou

I was wondering if it is possible to tell if the water was fresh or salty like our oceans. And if the water that is found on these other planets is found to be salty, what are the chances of it being as equally saline as our oceans. It makes one wonder where all this salt came from if these are all fresh water. Also, I know we did the return mission from capturing debris from a comet. We're they able to tell if that water was fresh or saline?

Rodmy Montero
Rodmy Montero

WHERE? I can't see the ocean from the provided picture. Not sketches or drawings for the underneath ocean?

Not enough news.

Nick Sawaya
Nick Sawaya

thats interesting and very good to know

Ganesh Gore
Ganesh Gore

Good news for our researchers and encouraging too !!!!

Mazhar Ali
Mazhar Ali

It is fascinating to know that the evidence of life elsewhere in our solar system is slowly but surely accumulating.

Mohan Ayyappan
Mohan Ayyappan

How come it is possible to take that much clear picture


yogesh kumar
yogesh kumar

IT IS GOOD TO US TO EXPAND OUR THOUGHT WHICH WOULD BE COME TRUE ON ONE DAY IN FUTURE REGARDING WE ARE NOT ALONE IN THIS UNIVERSE. THERE IS SOMETHING MUST EXIST WHICH HAS STARTED LIFE ON EARTH MILLIONS OF YEARS AGO. 

HENCE WE CAN SAY THAT WE ARE NOT ALONE DEFINITELY ........................... 

Gregory S.
Gregory S.

If you had asked 100 planetary scientists at the time voyager 2 flew by Saturn if they thought there could be life on any of the moons aside from Titan, I would bet you none would have considered it an even remote possibility. This just goes to show you just how much we have learned since then.

Didier Newman
Didier Newman

Then, perhaps, is there fossils or life expressions elsewhere? Is it possible? Isn’t the emergence and maintenance of life a process of radical contingency? That is, is a unique and unrepeatable past totally necessary? Or does life emerge through space like mushrooms when some conditions are present? So, how many conditions are necessary: three, four, trillions, infinite? Only one, water or any sort of God? Is God the word that means infinite conditions, absolute necessity? Anyway, how did the life that emerge in a given conditions resist when switching to a different  moment? How does life resist time itself, the effects of entropy? But, is it possible for human beings to recognize a simpler life than their own brain only? On the other hand, beyond likeness, is it possible to recognize a complex life than their brain, is this the extra-terrestrial life that some people are searching unsuccessfully? However, is there an origin of life or would it be as finding a cut in the material history of the universe, an infinite void that human language patches now? Along these lines, there is a peculiar book, a short preview in http://goo.gl/rfVqw6 Just another suggestion, far away from dogmas or axioms.

Andrew Booth
Andrew Booth

I'm often astonished by how features of planets and moons can be discovered by methods such as these. To be able to infer a subterranean ocean on Enceladus from the slight changes induced in Cassini's flight path is amazing. Full credit to those team members.

What a wonderful success Cassini has proved to be. The immediate future of space flight certainly appears to be vehicles such as Galileo, Cassini, Opportunity, Voyager etc.       

Marty Johnson
Marty Johnson

I love these stories and very much looking forward to finding out more about Ceres.

Christopher Barrett
Christopher Barrett

@Jenna Ioviero NASA also discovered arsenic life form in 2010, all be it bacteria, and it is known that there is sulphur life here on Earth, again bacteria.

Mahmood Khan
Mahmood Khan

@M. Akhtar  : I don't think they are looking for drinking water but rather signs of extra terrestrial life, because where there is water, there is life.

Andrew Booth
Andrew Booth

@Dwayne LaGrou The salt and minerals in Earth's oceans are dissolved from the surrounding substrate. A water cycle sees every drop of ocean water cycled through the rocks of the crust every 5 million years. Each drop is subducted at plate boundaries or forced many miles into the crust through pressure. The water is heated and absorbs salts and minerals before being ejected back into the ocean via seafloor springs and geothermal areas at mid-ocean ridges (such as the features we call black smokers). 

I think it's presumed that oceans on other planets absorb salts and minerals in exactly the same way the ocean does on Earth. For those oceans to be composed of fresh water would mean that a water cycle doesn't occur which would be most improbable.

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