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In the hunt for life outside Earth, Mars is old news.
“I think I would rank Enceladus now on Europe, and there were people who said Europe was a better prospect than Mars,” said Seth Shostak, senior astronomer at the SETI Institute, a nonprofit near of San Francisco who specializes in finding life outside of Earth. “So our ideas about where we might find creatures of some sort keep changing.”
Enceladus is an icy moon of Saturn, once overlooked by astronomers who thought it was too cold for life to evolve, much like they did with one of Jupiter’s moons, Europe. Now, thanks to several scientific discoveries that include potential chemical “biosignatures”, scientists have started to focus on the possibility that these celestial bodies may harbor microbial life.
There are already tantalizing clues that fundamental life forms may have evolved on other planets and possibly moons in the solar system. But as in most fields of scientific research, one step forward is sometimes followed by two steps back. For example, research in September that proposed phosphine gas in clouds of Venus could be a sign of life has since been thwarted by studies that question its findings.
Taken together, the studies indicate that the search for alien life in our solar system (scientists are also looking for life on exoplanets around distant stars and for radio signals that may have come from distant civilizations) has expanded beyond from an initial hypothesis that this might first be found on planets like Mars or Venus.
Several scientific papers this year address the search for faint signs of life in our solar system – with a June article on Enceladus offering one of the more intriguing perspectives.
Published in the journal Nature Astronomy, it is based on samples of water plumes ejected from Enceladus taken by the Cassini space probe from 2005 to 2015. The probe found high concentrations of methane and surprisingly high levels of hydrogen , which fit with the idea that microbes evolved to live around hydrothermal vents on the seabed, said Regis Ferriere, associate professor of ecology and evolutionary biology at the University of Arizona at Tucson and co- author of the study.
The Enceladus Ocean is believed to be made up of saltwater 12 to 15 miles deep, topped with up to 20 miles of icy crust. Scientists believe that it is heated by the movement of rocks in the moon’s core in Saturn’s intense gravitational field, and that cracks in the crust created by the same tidal forces eject water from the ocean into it. ‘space, Ferriere said in an email.
Methane in the ocean could be explained by purely chemical processes, he said. But the study showed it was “very likely” to have been made by microbes, as long as it was accepted that life could evolve around hydrothermal vents – a very controversial issue, he said. declared.
Hydrothermal vents at the bottom of the ocean on Earth – the so-called black smokers – thrive on microbes that feed on chemicals emitted by the vents and form the basis of a food chain that supports deep-water ecosystems whole tubeworms, shellfish and crustaceans without the sunlight necessary for photosynthetic plants. It is not known, however, whether life originally evolved there, or if it first evolved on the sunlit surface.
As scientists search for signs of life in the outer solar system, the debate over phosphine on Venus is still hot. Scientists first suggested in September that the phosphine gas they detected could be produced by microbes in its sulfuric acid clouds. Since then, other researchers have suggested that they may not have seen any phosphine at all; or that the phosphine is indeed the result of volcanoes; or that there isn’t enough water in the clouds to support any known life form anyway.
Jonathan Lunine, 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 could solve the questions of life on Venus – like the two missions announced last month by NASA.
Lunine also worked on the MISE instrument for NASA’s Europa Clipper mission, which will analyze infrared light reflected from Jupiter’s moon when it arrives there towards the end of this decade.
Europe, like Enceladus, is believed to have an underground ocean of liquid water beneath its frozen surface, although relatively little is known of it. But it’s believed to be older, bigger, and possibly warmer than the ocean on Enceladus, and it could turn out to be one of the most likely locations in the solar system for alien life to have evolved.
“We’ll just have to wait for Europa Clipper,” Lunine said.
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