Saturn’s moon Enceladus has looked like a tantalizing possibility for life in the Solar System for quite some time. Now, we may have identified something that can live there and explain why we found methane in its plumes.
Published in Nature Communications, a study led by the University of Vienna describes a particular microbe found in the deep sea near Japan called Methanothermococcus okinawensis that could survive the temperature, pressure, and chemical make-up of the ocean hiding under the icy surface of Enceladus.
They say this microbe suggests that methane detected in the plumes of Enceladus by NASA's Cassini spacecraft could be produced by microbial life, specifically methanogens – those that produce methane. And a future mission may be able to spot the biosignatures from such organisms hiding in its possibly warm ocean.
“Some of the methane detected on Enceladus could in principle be of biological origin,” Dr Simon Rittman from the University of Vienna, the study’s corresponding author, told IFLScience.
“We are the first ones to investigate whether microorganisms could possibly produce methane under these conditions.”
In their study, the team investigated three microorganisms in the laboratory to see if they could survive conditions on Enceladus and produce methane. This includes pressure of up to 90 bars (sea level pressure on Earth is about 1 bar), and temperatures as low as 0°C (32°F) but as high as 100°C (212°F) – if hydrothermal vents exist on the sea floor, as predicted.
The team performed the experiment in flasks 20ml in size, with a liquid inside composed of inorganic compounds. They added the microbes to the mixture, along with hydrogen and carbon dioxide – providing both food and energy, as expected on Enceladus.
Of their three microbes, they found that only M. okinawensis was able to survive the changing conditions. This microbe hails from the Archaea family and is found near hydrothermal vents in the Iheya ridge, near the Japanese island of Okinawa. The fact it survived showed that it’s possible for microbes like this (there could be many others) to survive on Enceladus.
“Our experiments show that under these conditions, as close as we can infer from the Cassini probe, this organism produces methane,” said Dr Rittman. “Hydrothermal vent systems would be the ideal habitat for the organisms we studied.”
With the Cassini mission coming to an end in September 2017, NASA is now investigating the possibility of sending a new mission to Enceladus at some point in the next decade or two. Proposals have included things like the Enceladus Life Finder (ELF)
To further answer the question of life on Enceladus, a future mission will need an advanced mass spectrometer – which can analyze the chemistry of the plumes – to detect possible biosignatures. It will need to be about five times as powerful as the one that flew on Cassini, able to detect lipids, proteins and amino acids from any extant life.
This study is not definitive proof that Enceladus is habitable. Information on Enceladus, and particularly its subsurface ocean, is extremely limited. But based on available data, it’s the best estimate we can make so far.
“The conditions simulated in the laboratory may not necessarily match those of the subterranean water ocean on Enceladus, which is based on extrapolations derived from the Cassini data,” Christa Schleper, head of the department Archaea Biology and Ecogenomics at the University of Vienna and a co-author on the study in a statement.
The study also highlights that, if it is possible for such life to survive on Enceladus, then we must be extremely careful about contaminating the moon. If Earth-based microbes were to hitch a ride on a future spacecraft and make it to the surface, it’s possible they could provide false readings of alien life in future.
Many questions about Enceladus remain unknown, including whether it even has enough energy to support organisms. But this study shows that, if it does have the right conditions, then it might just be a bastion for life outside Earth.
