Cassini noticed methane in Enceladus’ pens. Scientists do not know the way it could possibly be with out life

Even though the Cassini mission to Saturn ended almost four years ago, the data from the space probe still preoccupies the scientists. And the latest research, exploiting Cassini’s wealth of data, is perhaps the most compelling.

Researchers say they discovered methane in the clouds of Saturn’s icy moon Enceladus. The process by which the methane is produced is currently unknown, but the study suggests that the surprisingly large amount of methane likely came from activities at hydrothermal vents on the inner sea floor of Enceladus. These vents could be very similar to those in the Earth’s oceans, where microorganisms live, feed on the energy from the vents and produce methane in a process called methanogenesis.

“We do not conclude that life exists in the Enceladus ocean,” said Régis Ferrière, associate professor at the University of Arizona and one of the study’s two lead authors. “Rather, we wanted to understand how likely it is that the Enceladus hydrothermal vents are habitable for terrestrial microorganisms. It is very likely that the Cassini data tell us according to our models. “

One of the biggest surprises of the 13-year Cassini mission came in Enceladus, a tiny moon with active geysers at its south pole. Only about 500 km in diameter, the bright and ice-covered Enceladus should be too small and too far from the sun to be active. Instead, this little moon is one of the most geologically dynamic objects in the solar system.

In 2005, Cassini discovered jets made of water vapor and ice erupting from the surface of Enceladus. The water could come from an underground sea. Image source: Cassini Imaging Team, SSI, JPL, ESA, NASA

Breathtaking backlit images of the moon from Cassini’s camera show clouds erupting in Yellowstone-like geysers and emanating from tiger-stripe-shaped fractures in the lunar surface. The discovery of the geysers gained momentum when Cassini later discovered that the plumes contained water ice and organic matter. Since life as we know it depends on water, this small but energetic moon has been added to the short list of possible places for life in our solar system.

For the new study, the research team analyzed one of these materials ejected into space. They viewed the composition of the Enceladus cloud as the end result of several chemical and physical processes that take place inside the moon, where hydrogen, methane, and carbon dioxide are produced.

“We wanted to know: Could Earth-like microbes that ‘eat’ the hydrogen and produce methane explain the surprisingly large amount of methane that Cassini discovered?” Ferrière said in a press release from the University of Arizona.

First, the researchers assessed which hydrothermal production of dihydrogen would best fit Cassini’s observations and whether that production could provide enough energy to sustain a population of Earth-like hydrogenotrophic methanogens. To this end, they developed a model for the population dynamics of a hypothetical hydrogenotrophic methanogen, whose thermal and energetic niche was modeled on known loads on the earth.

Artistic rendering showing an internal cross section of Enceladus’ crust showing how hydrothermal activity can cause the plumes of water on the lunar surface. Credits: NASA-GSFC / SVS, NASA / JPL-Caltech / Southwest Research Institute

Then the research team ran the model to see if certain chemical conditions, such as the concentration of hydrogen in the hydrothermal fluid and temperature, provide a suitable environment for these microbes to grow. They also investigated the effects a hypothetical microbial population would have on their environment – for example on the escape rates of hydrogen and methane in the plume.

The team wrote in their paper published in Nature:

“We find that the observed escape rates (1) cannot be explained solely by the abiotic change in the rock core caused by serpentinization; (2) are consistent with the hypothesis of habitable conditions for methanogens; and (3) achieve the highest probability under the methanogenesis hypothesis, assuming that the probability of life arising is high enough. If the likelihood that life will develop on Enceladus is low, the Cassini measurements agree with habitable but uninhabited hydrothermal springs and indicate unknown methane sources (e.g. primordial methane) that will have to be discovered by future missions. “

“And the biological methanogenesis seems to be compatible with the data,” said Ferrière. “In other words, we cannot reject the ‘life hypothesis’ as highly improbable. To reject the life hypothesis, we need more data from future missions. “

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Natural paper
University of Arizona

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