There has been some really exciting developments in understanding what kind of life might exist in our own Solar System recently. The Cassini spacecraft showed us that hydrogen makes up some of the plumes of gas and stuff shooting out of Saturn’s moon, Enceladus. Now scientists have demonstrated that methane can be produced by microbes that feed on hydrogen and carbon dioxide in conditions very similar to those found on Enceladus.
Enceladus is not very big and scientists noticed a few years ago that there was a disturbance in the E ring of Saturn’s ring system that correlated with Enceladus’ orbit. Observations of the little moon showed it was pumping out something in geysers (pictured above in the image from NASA) created by the flexing of the moon due to tidal forces created in its orbit around Saturn. In April last year NASA announced that the Cassini mission had detected hydrogen in one of the plumes coming out of the moon. This was a very important discovery because the presence of hydrogen means that it is likely that deep inside the moon’s oceans there is hydrogen probably being pumped out via hydrothermal vents. This hydrogen then could provide a valuable energy source for microbes by combining with carbon dioxide to produce methane. This is a process called methanogenesis.
Scientists created conditions in the lab that would be very similar to those found in hydrothermal vents in the oceans of Enceladus that are probably present under the thick layer of ice encapsulating the moon. The Cassini mission helped identify that hydrothermal vents exist on the moon through the bits of silica detected in the plumes that Cassini flew through. The existence of this silica is best explained through the reaction of hot water on rocks. This discovery combined with the discovery of hydrogen in the vents as a potential energy source all point to the possibility that life could survive in a hydrothermal vent in the icy moon. It doesn’t mean there is life but that the condition are possible for life.
The microbes examined are from the Archaea domain of single celled organisms. These are very primitive forms of life and have no nucleus and may well have been some of the type of early life that formed on the Earth billions of years ago. One of these types of microbes called Methanothermococcus okinawensis (you can guess it’s something to do with methane and probably from Okinawa based on that name) was exposed to conditions that might be found in the hydrothermal events of Enceladus including the same mix of gases and high temperatures and pressures. The microbes got to work under these conditions and produced methane. The scientists, at the University of Vienna, also figured out that the combination of rock and gases in the vicinity of possible hydrothermal vents on Enceladus would produce enough hydrogen to sustain the microbes and their lab experiments showed they would grow under these conditions.
This is a huge development in astrobiology as it shows that life is a very real possibility in these extreme environments. There are no specific plans to send any more probes to Enceladus by either the European Space Agency or NASA so we may not know too much more about the composition of the geysers for a while yet. Helpfully though, Europa, orbiting Jupiter, has similar characteristics that may indicate a liquid ocean under the icy surface and the possibility of hydrothermal vents due to evidence of an eruption of water picked up by the Hubble Space Telescope. The Europa Clipper is due to launch in the 2020s to take a closer look.