When it comes to life, biologists have long hypothesised that its origins -- on Earth, at least -- were in thermal vents on the ocean floor, following a period of spontaneous metabolism before life began. Thermal vents are rich sites for marine life -- especially in Antarctica where, in the darkness under the ice, creatures proliferate in the warm, mineral-rich waters streaming from the vents.
It's just one of several theories, but if it's correct, Jupiter's moon Europa could be a very exciting place indeed. Ever since plumes of vapour were discovered on Jupiter's moon in December last year, NASA has been floating theories about the oceans that may be sloshing away under the layer of surface ice -- its similarities to theories about the early Earth look like it may have the ingredients for life.
"[There is] an ocean in our solar system that has been in existence for billions of years. It's an ocean that is perhaps ten times as deep as Earth's ocean. It's an ocean that is global and may contain two to three times the volume of all the liquid water on Earth. It's an ocean that exists beneath the icy shell of Jupiter's moon, Europa," said NASA astrobiologist John Hand in a new NASA video.
In its early days, before the formation of the ozone layer, Earth's atmosphere was largely devoid of oxygen, and we know that the Earth has been all but covered in a layer of ice in several ice ages past. These ice layers, which provided protection from harsh ultraviolet light and a crude atmosphere, combined with thermal vents -- sites of propagation for single-celled organisms -- could very well bear strong similarities to Europa, with its layer of ice and crude atmosphere.
Scientists at NASA's Jet Propulsion Laboratory are studying the life around these thermal vents on Earth in order to collect clues about what life on Europa might look like. In particular, they're looking at a type of shrimp called Rimicaris hybisae, living on one of the world's deepest hydrothermal vents, in the Caribbean Sea.
"For two-thirds of the Earth's history, life has existed only as microbial life," said JPL senior research scientist Max Coleman. "On Europa, the best chance for life would be microbial."
Life on thermal vents is able to survive extraordinarily harsh conditions; bacteria, for instance, survives without sunlight -- and therefore photosynthesis -- by relying instead on chemosynthesis: a process whereby organisms obtain energy from chemical reactions. In the case of bacteria on the hydrothermal vent, the bacteria use hydrogen sulphide produced by the vents to produce organic matter. Although hydrogen sulphide is toxic to organisms in high concentrations, the bacteria have adapted by positioning themselves directly between the sulphide-rich water and the normal ocean water.
These bacteria are then eaten by the shrimp. The shrimp live in the cooler water, avoiding searing temperatures of more than 750 degrees Fahrenheit (400 Celsius) using thermal receptors on their heads. The shrimp themselves, having no need of eyes where there is no light, are blind.
"The overall objective of our research is to see how much life or biomass can be supported by the chemical energy of the hot submarine springs," Coleman said. "You go along the ocean bottom and there's nothing, effectively. And then suddenly we get these hydrothermal vents and a massive ecosystem. It's just literally teeming with life."
If NASA could get an explorer to Europa to drill the ice and survey the moon, we could find out if it does, indeed, have an ocean with thermal vents on its floor -- and if extraterrestrial organisms live there. But it seems the thermal vents may be vital for fauna.
"Whether an animal like this could exist on Europa heavily depends on the actual amount of energy that's released there, through hydrothermal vents," JPL postdoctoral fellow Emma Versteegh said.