free debate

April 6, 2011

Scientific Unknowns: Life on Europa

Europa as seen by the Galileo Spacecraft. 
When we think of aliens we often think of a place similar to Earth. We think of creatures with similar body plans and similar needs. But what about the possibility of creatures that have never seen the Sun? This is the kind of life that could be hiding on Europa, Jupiter's fourth largest moon.

There are two sides to every claim, plausibility and evidence. Some claims, like many new medical drugs, start with a high plausibility but the evidence never bears them out. Others, such as quantum mechanics, start with low plausibility but the evidence becomes overwhelming until they are accepted. Right now, to my knowledge, there is no evidence of life on Europa. What makes it exciting, however, is how plausible it is that life could exist there.

Europa's entire surface is covered with ice. Located almost a half billion miles from the Sun, there is nowhere near enough heat from the sun to melt Europa's ice covered surface. Still many, if not most, scientists agree that there is likely a ocean under that ice. As Europa orbits around Jupiter, it is squeezed and stretched. This is what creates the cracks you see on the surface. This also heats Europa's core in the much the same way playing with Silly Putty will warm it up over time, creating a layer of liquid water. There is a lot of debate between scientists on how thick this ocean is. Right now, it seems likely that the ice is tens of kilometers thick with an ocean that is between 25 to 100 kilometers thick. So the question is could anything survive in the ocean?

A cutaway view showing Europa's interior. Notice the
inner rocky core surrounded by liquid water and capped
 off an outer layer of ice.
Credit: NASA/JPL
If there is any life in Europa's ocean, it have had to have formed and survive with no sunlight. The ice above this ocean is just too thick to allow in enough sunlight for any organism to use that as a source of energy. So scientists have looked to the Earth for creatures that can survive without the Sun. Probably the most similar environment to Europa here on Earth is the ocean under the Antarctic ice. When scientists have drilled into the ice there we have found life. In fact scientists have found entire colonies of organisms called black smokers that live in some of the harshest conditions on the Earth. These organisms live off of hydrothermal vents at the very bottom of the oceans where there is no light at all. Some scientists have even speculated that this is where life on Earth originated in the first place. These unique adaptations of life here on the Earth make it reasonable to think similar creatures could survive on Europa.

A hydrothermal vent on the
Mid-Atlantic Ridge. Credit NOAA
So when it comes to life on Europa we have a really good story. We have solid reasons to think the ocean is there and that life could possibly survive in that ocean. What we are missing is the evidence. A detailed study of Europa is high on NASA's priority list, but without the proper funding it could easily still be more than a decade away. At this point, we don't have the evidence to say if life exists on this icy moon or not. I hope in my lifetime a spacecraft arrives at Europa and drills through that ice. What we find in that ocean could change how we think about ourselves and the universe we live in.