NASA recently announced that they’re launching a mission to investigate Europa, an icy moon of Jupiter some 390million miles from Earth. The news has been met with widespread joy from just about everyone who possesses the remotest interest in science. So, what's the big deal? Put simply, recent scientific evidence appears to suggest that Europa represents our best chance of discovering alien life within our lifetimes. While NASA's first mission to Europa won't actually touch the surface, it is hoped that it will eventually lay the groundwork for the robotic and even human exploration of the moon's icy crust. It could be that some day in the next few decades, humanity will finally be able to answer the question of whether or not we're alone in the universe.
Liquid Water
Let's start with the obvious. Europa's outer crust is made up of solid ice a few miles thick, but it’s what’s beneath the crust that makes the moon so interesting. Scientists believe there is a liquid water ocean under the icy crust of Europa that reaches depths of over 100 miles, which is a big deal because as far as we know, life doesn’t exist without water. And not only is there lots of water, but it’s thought to be highly active water, constantly being churned, and therefore heated, thanks to Jupiter’s strong gravitational pull. “Nothing grows or reproduces when the water activity falls below some pretty high value, actually,” says NASA scientist Christopher McKay. “Microorganisms need surprisingly wet conditions.” It’s also worth noting that current estimates suggest that Europa has more liquid water than planet Earth, and last we checked Earth had a solid amount of life.
Lots of Oxygen
Another key to life on Earth is oxygen; it would be pretty tough to breathe without it. When it comes to O2, Europa has us covered. A recent study by University of Arizona's Richard Greenberg revealed that Europa has roughly enough oxygen to support 3 million tons of alien fish. But before we start celebrating, there's the small issue of Europa potentially having too much oxygen. An abundance of O2 can actually end up inhibiting the chemical processes necessary for life to form, but Greenberg thinks he’s figured out this problem, too, arguing that the amount of time potential organisms would have had to figure out how to use the oxygen on Europa before it became too plentiful (over a billion years) is the same amount of time it took life on Earth to develop before oxygen levels became too high. We like that comparison.
Cracks in the Ice
Ok, so there’s lots of water and oxygen, but is there a way for the oxygen and other chemicals to reach the water in the right amounts to sustain life? Thanks to deep cracks present in Europa's icy crust, there just might be. The Hubble Telescope has observed geysers of water bursting up from the surface of Europa, suggesting a pathway from the atmosphere through the ice to the ocean below. This could potentially allow chemicals to reach the ocean, something that excites Steve Vance, a member of NASA’s Europa mission science team. “When I think about the fluxes of oxygen to Europa's ocean, I wonder if Europa could have the kinds of vigorous biosphere that Earth has that supports larger forms of life,” Vance says. “And then the imagination can go wild thinking about fish and octopi and whatever else might live in an ocean that's 100 kilometers deep.”
Hydrothermal Vents
Despite all we’ve discussed, there’s still the issue of Europa’s harsh climate. The moon’s surface temperature never creeps above -260°F, which is, shall we say, a bit too chilly for life as we know it. But there may be a way around that. In the most hostile environments on Earth, we still find life deep underwater near hydrothermal vents, where heat rises from deep inside the planet and provides energy for life that doesn’t have access to sunlight. “It's the only system we know of on Earth where life can thrive in the complete absence of sunlight,” says scientist Bob Vrijenhoek of the Monterey Bay Aquarium Research Institute. Scientists believe the ocean floor of Europa has similar vents, and if it does, life could be there as well. It’s not little green men, but it’s a start.
