NASA is trying to answer a deep question: if we ever find alien life in the universe, how will we figure it out? Whatever it is in space, it can be truly strange and unrecognizable. When the robotic probe lands on a watery world like Jupiter's Europa, what should scientists see in order to throw up their hands, slap the table and, adjusting their glasses on the bridge of their nose, say: is this life?
Retired astronaut John Grunsfeld is also concerned about this question. If anything, it became clear when he answered questions about the agency's scientific missions in 2002.
“We looked at him stone-faced,” recalls Jim Green, head of NASA's planetary science division. “What do we need to build to truly find life? What tools, what methods, what objects to look for? Finding life means defining life first and foremost, and Greene says that the main functions that are now emerging are metabolism, reproduction and evolution. Life should show these signs.
In late December, NASA asked the prestigious National Academy of Science, Technology and Medicine to bring together leading experts in astrobiology for a meeting to discuss the current state of the search for extraterrestrial life in the solar system and extrasolar planetary systems.
There is growing interest in biosignatures - or substances that provide evidence of life - as NASA prepares missions to potentially detect them. These include a visit to Europe in the 2020s and the launch of the James Webb Space Telescope in 2018, which will scan the atmospheres of planets near other stars.
What NASA wants to avoid at all costs is repeating the experience of the Viking missions back in the 1970s, when analysis of the chemistry of the Martian soil first yielded evidence of life in it, and then was considered false positive. The authors of the experiment are still trying to prove that the Vikings did find life.
“I remember the consequences of this,” says James Casting, professor of geosciences at Pennsylvania State University. “NASA has been heavily criticized for finding life on the planet that needed to be explored first, and for not being careful enough to experiment. They hope to avoid repeating this."
But getting this definition doesn't mean coming to a consensus on what to look for. “We have a heated debate about this,” says Casting. "That's why we got together, actually."
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In our own solar system, scientists are wondering what kind of extinct or extinct life we might find on Mars, on the icy moons of Europa and Enceladus, or in Titan's strange methane lakes. If scientists find DNA or RNA, obviously, this will be a direct indicator of the existence of something alive, if, of course, the possibility of contamination is excluded.
But alien life is unlikely to be composed of the same type of genetic material. In fact, her chemistry can be completely unrecognizable. “If I just start following the routine procedures for finding life as we know it on Earth, there’s no reason to believe it will help define life with slightly different biochemistry,” says Steve Benner of the Applied Molecular Evolution Foundation. "It would be rather strange looking for long, elongated molecules separated by regularly repeating sections."
Finding life outside of our solar system presents other challenges, as there is no interstellar travel that would allow a spacecraft to visit a planet around another star and study the dirt on its surface. All scientists can do is look through a telescope and sift through the light for clues."
With such constraints, Benner says, perhaps the best we can do is seek out life on earth. However, not all scientists agree with him. An unambiguous signal from a distant planet in another system would be the presence of large quantities of oxygen and gases like methane or nitrous oxide.
"Both oxygen, methane and nitrous oxide are produced primarily by biology, so it is very difficult to create high concentrations of these gases, especially two or three at the same time, in the absence of life," says Casting.
“As a field geologist, I strongly believe that we need to send people like me to the surface of Mars, open up a bunch of rocks and look for signatures of the first Martian life,” says Ellen Stofan, who recently left NASA. “Because it’s not enough just to say: well, we have one molecule that has a biological origin. It takes many molecules, many specimens, to understand the state of life beyond Earth. The thought that in the next 20 years we will finally begin to answer these questions is literally dizzy."
ILYA KHEL
