Why the moons of Jupiter and Saturn may be key to finding alien life

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In the search for extraterrestrial life, Mars is old news.

“I think I would now base Enceladus on Europa, and there were people saying that Europa was a better prospect than Mars,” said Seth Shostak, chief astronomer at the SETI Institute, a nonprofit near San Francisco that specializes in research. for life outside Earth. “So our ideas about where we might find creatures of some kind are constantly changing.”

Enceladus is an icy moon of Saturn that astronomers once overlooked, finding it too cold for life to evolve, just as they did with one of Jupiter’s moons, Europa. Now, thanks to several scientific discoveries involving possible chemical “biosignatures,” scientists are beginning to focus on the possibility that these orbs may harbor microbial life.

There is indeed tantalizing evidence that basic life forms may have evolved on other planets and possibly the moons of the solar system. But like most areas of scientific research, one step forward is sometimes followed by two steps back. For example, research conducted last September, which suggested that the proposed gas phosphine in the clouds of Venus could be a sign of life, has since been countered by studies questioning their findings.

Taken together, the studies suggest that the search for extraterrestrial life in our solar system (scientists also search for life on exoplanets around distant stars, and for radio signals that may be from distant civilizations) has expanded well beyond the initial assumption that it might be the first . It can be found on planets like Mars or Venus.

This illustration shows Cassini diving through the Enceladus plume in 2015.

Several scientific papers this year address the search for faint signs of life in our solar system — with a June paper on Enceladus offering one of the most intriguing possibilities.

Published in Nature Astronomy, it is based on samples of water plumes from Enceladus taken by the Cassini space probe from 2005 to 2015. The probe detected high concentrations of methane and unexpectedly high levels of hydrogen, which fits with the idea that microbes have D., associate professor of ecology and evolutionary biology at the University of Arizona in Tucson and one of the study’s authors, it evolved to live around hydrothermal vents on the sea floor.

The ocean on Enceladus is believed to consist of salt water 12 to 15 miles deep, topped by up to 20 miles of icy crust. Scientists believe it’s being heated by the motion of the moon’s core rock in Saturn’s intense gravitational field, and cracks in the crust caused by the same tidal forces are throwing water from the ocean into space, Ferrer said in an email.

Saturn’s moon Enceladus, imaged by NASA’s Cassini spacecraft on October 28, 2015. NASA/JPL-Caltech

He said the methane in the ocean could be explained by purely chemical processes. But the study showed it was “highly likely” that microbes made it, as long as it was accepted that life could evolve around hydrothermal vents — a much-controversial question, he said.

Hydrothermal vents on Earth’s ocean floor – so-called black smokers – thrive on microbes that feed on chemicals emitted from the vents and form the basis of a food chain that supports entire deep-sea ecosystems of tubeworms, shellfish and crustaceans without the sunlight required by plants that process Photosynthesis. However, it is not known whether life originally evolved there, or if it first evolved on the sunlit surface.

While scientists search for signs of life in the outer solar system, the debate over phosphines on Venus remains heated. Scientists first suggested in September that the phosphine gas they discovered may be from microbes high in clouds of sulfuric acid. Since then, other researchers have suggested that they may not have seen phosphine at all; or that phosphine is really the result of volcanoes; Or that there isn’t enough water in the clouds to sustain any known form of life anyway.

View this artist showing a cut view of the interior of Saturn’s moon Enceladus, October 26, 2015. NASA/JPL-Caltech

Jonathan Lunin, a professor of astronomy at Cornell University and co-author of the study published Monday that suggests phosphine could be caused by volcanoes, said only future space probes can solve questions of life on Venus — like the two recently announced missions. . month by NASA.

Lunine also worked on the MISE instrument on NASA’s Europa Clipper mission, which will analyze the infrared light reflected by Jupiter’s moon when it reaches there near the end of this decade.

Europa, like Enceladus, is believed to have a subterranean ocean of liquid water beneath its frozen surface, although relatively little is known about it. But it is thought to be older, larger, and possibly warmer than the ocean on Enceladus, and could prove to be one of the most likely places for extraterrestrial life in the Solar System.

“We just have to wait for the Europa Clipper,” Lunin said.

Tom Metcalfe

Tom Metcalfe writes about science and space for NBC News.

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