Some of you may have heard that Jupiter’s moon, Europa, is a likely to find life in our Solar System. This may sound odd. Europa is, after all, terribly far from the Sun. How could it host liquid water, let alone the photosynthesis that makes up the base of most of Earth’s ecosystems?
At a glance, you’d be right. Europa orbits Jupiter, which is about five times further from the Sun than earth. Its surface temperature can dip unsettlingly close to absolute zero. Plus, it’s pretty tiny–about 100 Europas could fit inside the Earth. The fact that Jupiter’s titanic magnetic field creates enough radiation on Europa’s surface to kill a human in five minutes is just sort of a perk. The cold would get you first.
But if we look closer, Europa has a lot to teach us about where life might arise in the Universe. It turns out that the bitter cold and the deadly force of Jupiter work together in an almost absurdly convenient way to make Europa a possible incubator for life.
Measurements of Europa’s magnetic field reveal that its entire surface is covered by liquid water about 62 miles deep. (Diagram of Europa’s interior, complete with magnetic field lines, courtesy of NASA.) Well, not its surface–its surface is a crust of ice whose exact thickness is not known. But that entire ice crust appears to float atop a 62-mile-deep saltwater ocean. That’s kind of a lot of water. Earth’s deepest ocean trench is only 6.8 miles deep.
How is that possible without sunlight? Europa owes its warmth to Jupiter’s immense gravitational pull. It’s so strong that as she orbits, Jupiter’s gravity stretches and squeezes Europa–creating friction. A lot of friction. Enough friction to keep some of Jupiter’s less watery moons partially molten, and apparently enough to melt water on Europa.
The ridiculously convenient part? Europa’s solid ice covering could provide one of the best shields imagineable from Jupiter’s deadly radiation. Due to its molecular characteristics, water shielding is actually toward the top of the list of ways NASA hopes to protect humans from radiation in space.
Where there’s enough heat to thaw ten Earth oceans’ worth of ice, there’s probably enough heat to support life. On Earth, photosynthesis supports most food chains–not all of them. Earth, in fact, has thriving deep-sea ecosystems which survive off the heat and chemical energy of water heated by Earth’s molten core. Some scientists even believe that life on Earth may have started at these deep-sea hydrothermal vents.
And hydrothermal vents aren’t the only examples of lightless ecosystems we have on Earth. There’s another kind that doesn’t even require intense heat. Cold seeps on Earth survive at near-freezing temperatures off of chemical energy from life forms that died and were buried on the sea floor millions of years ago.
These deep sea communities are very alien, and very cool. (Ha. Ha. That’s half punderful.)
Hydrothermal vent communities on Earth are gorgeous. (Image at right courtesy of NOAA. Science: one thing to love about our government.) Defying expectation for an environment that’s naturally pitch-dark, tube worms, crabs, and other communities are found in brilliant contrasts of red and white. Some of the animals there, like the crabs, look like things we’re used to seeing on the surface and may be the recent descendents of surface creatures. Others are completely alien and unique.
Take the trademark creature of the hydrothermal vent, the tube worm. These look kind of like a cross between a celery stalk and a sea anemone. Long, vegetable-like white body stalks end in brilliant red foliage/plumage that waves in the current but will retract like a snail’s eye if you poke it. The weirdest part: this plumage is red because it’s full of hemoglobin. You know, the oxygen-carrying pigment in human blood. The tube worms are full of something remarkably like human blood.
And in keeping with the bizarre plant-animal hybrid theme, they have blood, but they have no digestive tract. Instead of stomachs, the tube worms have special organs called trophosomes that are full of symbiotic bacteria. These bacteria turn toxic inorganic molecules like hydrogen sulfide and carbon dioxide from the water that comes out of the vent into organic molecules, which the worm feeds on. This “chemosynthesis” drives entire thriving ecosystems.
Then, there are cold seeps. These are exponentially more bizarre. Cold seeps lack even the familiar trapping of heat that we’re used to associating with life. And they have some positively spooky features–like the supersaturated salt water that creates “lakes,” complete with breaking waves, underwater. These really freaked scientists out the first time they found one (see video at bottom for lulz).
Cold seeps also play host to creatures that appear to be relatives of hydrothermal vent dwellers. There are tubeworms–with some significant anatomical differences to adapt to the cold–and bright organe bacteria that form thick matts along the bottom. There are corals, and even mussels that have symbiotic relationships with methane-eating bacteria much like those of the tubeworms and the hydrogen-sulfide eaters of the hydrothermal vents. But, being completely different species this symbiosis likely evolved at least twice independently. Curious.
One especially interesting feature of cold seep life is the effect the cooler temperatures have on metabolism. They slow it down. While life near hydrothermal vents happens at a fast pace, with organisms swiftly growing, dying, and being replaced–scientists believe that the individual tube worms found at cold seeps may take hundreds of years to grow. That may not be the most exciting thing in the world–tube worms taking hundreds of years to grow. But the thought of whole ecosystems composed of ancient creatures is sort of humbling.
Because we don’t know how life may have originated on Europa–or what forms it may take–we can’t say a huge amount about what life on that planet might look like. But here are some body types that have worked in Earth’s deep seas, in defiance of our photosynthesis-centric worldview.
Update: The recent discovery of unique hydrothermal vent communities on Earth near Antarctica may be relevant to our interests: http://news.yahoo.com/yeti-crabs-ghost-octopus-unique-life-found-1st-220903638.html