Methane escaping from Enceladus may be a sign that life is swarming in Saturn’s moon’s underground sea, a new study reports.
In 2005, NASA’s Cassini Saturn The orbiter discovered geysers hurling water ice particles into space from “tiger stripe” fractures near the south pole of Enceladus. This material, which forms a plume that feeds Saturn’s E ring (the second outermost ring on the planet), is believed to come from a huge ocean of liquid water lapping beneath the moon’s icy shell.
And it’s not just water ice in the plume. During numerous close flights of the 313-mile-wide (504-kilometer) Enceladus, Cassini spotted many other compounds – for example, dihydrogen (H2) and a variety of organic compounds containing carbon, including methane (CH4).
Pictures: Enceladus, the cold and bright moon of Saturn, in pictures
Dihydrogen and methane are particularly intriguing to astrobiologists. H2 is likely produced by the interaction of rock and hot water on the seabed of Enceladus, scientists said, suggesting that the moon has hydrothermal vents in deep water – the same type of environment that may have been the cradle of life here on Earth.
Additionally, H2 provides energy to certain microbes in the land that produce methane from carbon dioxide, in a process called methanogenesis. Something similar could be happening on Enceladus, especially since Cassini also spotted carbon dioxide and a surprising amount of methane in the moon’s plume.
âWe wanted to know: Could Earth-like microbes that ‘eat’ hydrogen and produce methane explain the surprisingly large amount of methane detected by Cassini? Â»Co-lead author of the study, RÃ©gis FerriÃ¨re, associate professor in the department of ecology and evolutionary biology at the University of Arizona, said in a press release.
FerriÃ¨re and his colleagues therefore built a series of mathematical models that evaluated the probability that Enceladus’ methane was generated biologically. These simulations were diverse; the team investigated whether the observed H2 production could support a population of Enceladus microbes, for example, and how that population would affect the rate at which H2 and methane escape through the plume, among other things.
“In summary, not only could we assess whether Cassini’s observations are compatible with a lifelong habitable environment, but we could also make quantitative predictions about the observations to be expected, if methanogenesis actually occurred on the Enceladus seabed. “said FerriÃ¨re.
This assessment should cheer those of us hoping for something to swim in the frigid, dark sea of ââEnceladus. The team determined that the chemistry of abiotic hydrothermal vents (without the aid of life) as we know it on Earth does not explain very well the concentrations of methane observed by Cassini. The addition of the contributions of methanogenic microbes, however, fills the void well.
To be clear: the new study, which was published last month in the journal Nature Astronomy, does not claim that life exists on Enceladus. For example, it is possible that the icy moon exhibits certain types of methane-producing abiotic reactions that are not prevalent here on Earth – possibly the decay of the primordial organic matter left behind by the birth of the moon, the researchers said. . Indeed, this last hypothesis would be perfectly suitable if Enceladus were formed from matter rich in organic matter supplied by comets, as some scientists believe.
âPart of it boils down to the likelihood that we think different assumptions are at the start,â FerriÃ¨re said. “For example, if we consider the probability of life in Enceladus to be extremely low, then such alternative abiotic mechanisms become much more likely, even though they are very foreign to what we know here on Earth.”
That being said, “biological methanogenesis appears to be compatible with the data,” Ferrier added. “In other words, we cannot dismiss the life hypothesis as highly improbable. To reject the life hypothesis, we need more data from future missions. “
Mike Wall is the author of “Over there“(Grand Central Publishing, 2018; illustrated by Karl Tate), a book on the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.