When trying to imagine what alien life would be like, it makes sense to delve into the most extreme environments our planet has available. Precisely one of those places where life has thrived is 3 kilometers underground : it is home to one of the strangest forms of life we know: the bacterium Desulforudis audaxviator , known as Audacious Traveler.
The Audacious Traveler lives in complete darkness, in groundwater of up to 60 ºC, in an environment devoid of sunlight, oxygen or organic compounds. Despite this very particular scenario, this organism has evolved perfectly, obtaining its energy from the radioactive decay of uranium from the rocks around it, which means that it lives on nuclear energy instead of depending on the sun.
This, according to researchers from the Brazilian Synchrotron Light Laboratory and the University of São Paulo , make it an excellent model to study the possibility of extraterrestrial life (as on Jupiter’s moon Europa, which apparently may have similar hydrothermal vents. to those of the Earth).
“We studied the possible effects of a biologically possible energy source in Europe based on information obtained from an analogous environment on Earth,” commented Douglas Galante, leader of the work.
But it is that the Audacious Traveler goes a step further. Discovered in 2008, it was the only bacteria found in groundwater samples at the Mponeng gold mine in South Africa, where it has lived for millions of years. It was totally alone in its ecosystem, as it does not even feed on any other species.
“This deep underground mine has water seeping through cracks that contain radioactive uranium,” explained Galante.
“Uranium breaks down water molecules to produce free radicals. Free radicals attack surrounding rocks, especially pyrite, producing sulfate. Bacteria use sulfate to synthesize ATP [ Adenosine triphosphate ], the nucleotide responsible for storing energy in cells. cells. This is the first time that an ecosystem has been found to survive directly on the basis of nuclear energy “, clarifies Galante.
The researchers argue that the conditions in which this bacterium has lived for so long are also plausible on the moon Europa.
According to NASA, three ingredients are needed to make Europe habitable: water, heat, and the chemicals necessary to fuel life.
Water and heat are plausible in Europe. The chemistry is the hardest part to confirm, as we currently do not have a means of sampling the waters of Europe. But, depending on the presence of radioactive materials in the solar system, they may also exist there.
“Their presence had been detected and measured on Earth, in meteorites reaching Earth and on Mars. So we can say with some certainty that this must have happened in Europa as well,” Galante said.
“In our study, we work with three radioactive elements: uranium, thorium and potassium, the most abundant in the terrestrial context. Based on the percentages found on Earth, in meteorites and on Mars, we can predict the amounts that are likely to exist in Europa ” .
NASA plans to send a spacecraft to Europa to help find answers. It will launch between 2022 and 2025, and it will orbit Jupiter to track observations of Europa made by the Galileo spacecraft.
“The ocean floor in Europa appears to offer conditions very similar to those that existed on early Earth during its first 1 billion years. Therefore, studying Europa today is, in a way, like looking back at our own planet in the past. “Galante concluded.
Reference: Microbial habitability of Europa sustained by radioactive sources. Nature 2018. doi: 10.1038 / s41598-017-18470-z
