Saturday, December 15, 2012


My favorite moon, other than the one orbiting the Earth, has got to be Europa. Jupiter's sixth moon is special in one incredible way that makes it stand out among all the other moons in the solar system.

Europa. Source

You may have noticed that this moon looks a bit odd. Most of the rocky bodies in our solar system are barren hunks of rock floating dead in space, pitted and scarred with impact craters from numerous run-ins with space debris. You'd never expect to find long, unbroken lines marring the surface of any of these objects, yet Europa abounds with long, river-like markings. But it is not the appearance of Europa that makes it special, it is the reason for this appearance that sets it apart. The entire surface of the moon is water ice. That's right, Europa has water, a lot of it.

The surface of Europa even looks like it's made of ice. Source

The lines on the surface of Europa are cracks in the surface of the ice. Tidal flexing, caused by the moon's rotation and the gravity of Jupiter, cause these cracks, creating a process similar to plate tectonics on Earth. This tidal flexing could also be doing something much more interesting than cracking ice. It is likely that this tidal flexing is creating heat in the moon's core, and thus could be causing the water ice below the surface to melt. If there is liquid water, protected from space by the shell of ice, on Europa, then it is entirely possible that there is also life on the large moon.

Europa likely has an abundance of liquid water. Source

I think it's time for some boring facts before getting back to the question of life. Europa is slightly smaller than Earth's Moon, making it one of the largest moons in the entire solar system. The interior of the moon is likely silicate rock surrounding a small iron core. Beyond the rocky center of the planet should be a fairly thick sheet of liquid water. It is important to note that water has the special property of expanding when it freezes. This is important because it means that a large amount of water could be kept liquid at fairly low temperatures and gravity because the icy sheath of the moon could act as a sort of pressure chamber. All that would be needed would be some extra heat from the moon's core which, as I've mentioned, could be supplied by tidal flexing. Beyond the icy surface of Europa, there is extremely little atmosphere. Just a little bit of oxygen floating around. 

Europa orbits once of every two rotations. Source

Back to the question of life on Europa. Before I start making any claims, let me first state that there is no evidence of life on Europa. This is all speculation.
As the ice surrounding Europa cracks, water spews forth to close up the cracks. Because of this upwelling, we know that water exists, the question is how much and at what temperature. In Earth's oceans there are entire ecosystems living around geothermal vents that don't require light from the sun. These ecosystems survive off of bacterial that are capable of living off of the heat and reactive chemicals coming from these vents. It is possible, even likely, that similar vents exist on Europa. If these vents do exist it is entirely likely that bacteria and other simple organisms could live on Europa. If these bacteria do exist then it's possible that other, larger organisms could live off of them. The problem with this, however, is that the larger organisms that survive around geothermal vents on Earth also rely on oxygen, something that likely doesn't exist in the oceans of Europa. It is possible that life on the large moon could find some other way of life independent of oxygen, but Richard Greenberg posits that they might not have to. He claims that cosmic rays that hit the surface of Europa could convert some of the water ice into oxygen which could then be absorbed into the subsurface oceans through the cracks that form in the ice. This would be a slow process, but eventually it could put enough oxygen into the oceans for large, aerobic organisms to survive. 
I don't know what's down below the ice on this moon, but whatever we find, it won't be an ecosystem as large or diversified as the one on Earth. Our planet is just too conducive to life for Europa to ever match.

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