Scientists have discovered the strongest evidence yet of extraterrestrial, liquid water. A study of NASA images show evidence of underground lakes as big as the Great Lakes on Earth below the surface of Jupiter’s icy moon Europa.

In a study led by planetary scientist Britney Schmidt of the Jackson School of Geosciences at the University of Texas, Austin, Jupiter’s ice-covered Europa shows lumpy, cracked areas called chaos terrains that researchers say are caused by movement of trapped pools of water in the ice.

Dr. Schmidt told EarthSky:

The real evidence for the lakes is the fact that at one location, one of these chaos terrains called Thera Macula, the surface is depressed in a large, circular area. And that circular area is around 100 by 100 kilometers. It’s relatively large, about the size of Lake Ontario. But the surface has dropped down by about 400 to 600 meters in this whole area. The big icebergs have kind of cracked up, and they’re floating along higher than that lowest point. And what that tells us is that the material below this feature on the surface is still liquid. So there’s a giant lake. If you use how much the surface is depressed as an indicator of about how much is below that, then you get an answer that is a lake that is 3-4 kilometers deep, which is in fact the depth of the Earth’s oceans.

The study, published late November 2011 in the journal Nature, re-examined images gathered by NASA’s Galileo orbiter, which probed the planet Jupiter and its moons from 1995 to 2003. Galileo took took stereo images of Europa’s icy surface, which gave researchers ability to measure the height of geologic features such as dome-shaped ice rises and ice bergs, and lumpy material called matrix. Dr. Schmidt said this:

Inside this ice shell, we have this evidence for trapped, liquid water bodies. And it’s basically because the icebergs are floating. The surface is depressed down, which tells us that it melted, and the icebergs are floating, which tells us that it’s floating on water. When you look someplace else on the surface, where you see these domes that have formed, those domes can’t form if the water has drained away. That’s what tells us that that water body is trapped inside the ice shell. So it’s not melting through the entire ice shell, but there is this liquid lake that’s formed up near the surface, just below the surface of the ice, but is trapped up inside the ice, initially at least.

Dr. Schmidt said that the evidence has been mounting of vast pools of water beneath the ice shell of Europa. In addition to imaging, NASA’s Galileo spacecraft also measured the Jovian moon’s magnetic field, which found a layer inside Europa that conducts electricity, indicating a strong possibility of salty water. Schmidt told EarthSky:

This global ocean, we’ve known for a while. What hasn’t been known is how much water might get up close to the surface of Europa. Basically, this is the best evidence for large amounts of it.

Jupiter’s volcanic moon Io rains salts and other minerals such as sulfates and magnesium onto the surface of Europa, which according to Schmidt lowers the melting point of its icy shell and makes it easier to form the cracks seen at the dome-like chaos terrains. Those minerals could fuel the possibility for life. She said:

At Europa, we think there are these ingredients for life — water, chemical energy, the things that we think we need. From the perspective of this paper, what we’re saying is the ice shell is overturning actively. And so if the ice shell is overturning — I mentioned all of this material is raining down on the outside of Europa, and it’s going to be sitting on that brittle ice — as that ice overturns, it gets pulled down into these lakes. When that lake re-freezes, that ice is now much deeper in the ice shell. And so it can be pulled back down. It’s heavier than the ice around it. That oxidant-rich ice can now be pulled down into the ocean. It’s basically like a highway, bringing food for the ocean down through the ice shell.

The next steps in understanding what water lies in Europa might be gained ice-penetrating radar, the technology used to map out the structures of ice at Earth’s poles. Said Schmidt:

On Europa, the rock is down below the ocean. And the ice shell is floating. So features like these giant lakes, because there’s only a few percent density contrast between ice and water, you might not even be able to detect them with gravity. The reason I think ice-penetrating radar is likely to be important is because of the ability to really see those features and go looking for water, divining water on Europa. In terms of how that ice shell works, which is something of an unknown at this point, I think that’s going to be the most important thing to constrain for understanding how Europa works. Of course I’d like to go back and land one day. I think anybody who is interested in Europa wants one day for us to go back and land and answer, is life there? What’s down there? But you want to give yourself the best chance to succeed. So from my perspective, I’d like to have that answer about how the ice shell works, so I know where to land in the first place. I think all of those answers are out there, and hopefully in the next few decades we do go back.

Bottom Line: Scientists have discovered underground lakes as big as the Great Lakes on Earth below the surface of Jupiter’s moon Europa. Evidence is mounting that Europa contains the liquid water, combined with the right chemistry, to possibly support life. It will take future space probes to find out for sure.



EarthSky 22: Other Earths? Other lifeforms?

Steve Squyres looks ahead to next 10 years of space exploration of planets



Bill Stone: Robot sub, alien life, Jupiter’s moon