Ask Ethan: How Can Worlds That Never Get Above Freezing Have Liquid Water? (Synopsis)

"Day after day, day after day,
We stuck, nor breath nor motion;
As idle as a painted ship
Upon a painted ocean.
Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink." -Samuel Taylor Coleridge

Here on Earth, water can easily exist in all three phases of matter: solid, liquid, and gas. The reason for this is simple: Earth has the right range of temperatures and pressures to experience not just the common solid and gas phases, but the liquid water phase, too. In the outer Solar System, worlds like Europa, Enceladus, and Pluto are too far from the Sun to ever reach surface temperatures high enough to create a liquid phase; it seems that water is a no-go.

Europa, one of the solar system's largest moons, orbits Jupiter. Beneath its frozen, icy surface, a liquid water of ocean is heated by tidal forces from Jupiter. Image credit: NASA/JPL-Caltech/SETI Institute/Galileo Orbiter.

But there must be subsurface oceans on these worlds! Not only is there geological evidence of an ocean beneath a thick layer of ice, but on some worlds, like Enceladus, we can actually see large plumes of liquid water ejected hundreds of kilometers above the surface, like some sort of planet-scale geyser. While the increased pressure from the ice plays a role, it isn’t enough on its own; there must be other factors, too.

The tidal forces acting on Saturn's moon Enceladus are enough to pull its icy crust apart and heat the interior, allowing the subsurface ocean to erupt out hundreds of kilometers into space. Image credit: NASA / JPL-Caltech / Space Science Institute.

How do worlds that never get above freezing actually come to have liquid water on their surfaces? Find out on this week’s Ask Ethan!

More like this

"Aha! That satellite was scuttled on Enceladus, Saturn's main dump moon!" -Professor Farnsworth, Futurama When you think about life beyond Earth, you likely think of it occurring on a somewhat Earth-like planet. A rocky world, with either a past or present liquid ocean atop the surface, seems ideal…
By Dr. Cynthia Phillips Planetary geologist at the Carl Sagan Center for the Study of Life in the Universe, SETI Institute Jupiter's moon Europa could be the best place beyond the Earth to search for life. This small moon, about the size of Earth's Moon, is one of the Galilean moons first…
Neat. One of the moons of Saturn, Enceladus, has cracks and eruptions that couldn't be explained by heat. (It is much too small to have volcanic actiivty.) They think that the cracks might be caused by tidal forces from Saturn's gravity: In 2005, the Cassini spacecraft flew by Enceladus and saw…
This sweeping mosaic of Saturn's moon Enceladus provides broad regional context for the ultra-sharp, close-up views NASA's Cassini spacecraft acquired minutes earlier, during its flyby on Aug. 11, 2008. See PIA11114 and PIA11113 for the higher resolution views. This false-color mosaic combines…