Our task is not only to find life, but also to understand that it is really alive. This is very difficult to do, since humanity does not have such an experience.
Our attempts to search for alien life forms still stumble upon a significant difficulty: we know what it is from a single example. Therefore, the search for traces of life or any biological manifestations on other planets mainly focuses on molecules like those used by terrestrial life. They are looking for on Mars, and on Europa they will look for amino acids, unequal amounts of "right" and "left" molecules and unusual ratios of carbon isotopes. These are all signatures of life here on Earth.
However, there is nothing forcing potential inhabitants of Europe to follow other people's rules of the game. What if they are arranged completely differently and their life is absolutely different from the earthly one? “I think there is a real possibility that we could skip life if its similarity to Earth was the only criterion,” says Mary Voytek, head of NASA's astrobiology program.
Lee Cronin, a chemist at the University of Glasgow, has proposed a solution to this problem. He argues that life stands out from inanimate nature for its ability to create very complex structures. They must be looked for, regardless of how "it" is arranged and what it consists of. “Biology has one signature: the ability to do complex things that could not have arisen in the natural environment on their own,” says Cronin.
Lee Cronin. Photo Wikipedia
Obviously, an airplane or a mobile phone could not have arisen by itself, so their existence points to a living and even intellectual - to what created them. Simpler things, such as proteins, DNA molecules, or steroid hormones, are also unlikely if they were not prepared by a living organism.
Cronin devised a way to measure the complexity of a molecule by counting the number of unique steps it takes to form it - for example, adding groups of atoms like hydroxyl or benzene. “Any structure requiring more than 15 steps is so complex that it must be of biological origin,” he said this week at the Astrobiology Science Conference in Mesa, Arizona.
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This criterion can be made even simpler by calculating the maximum molecular weight for compounds that can assemble spontaneously.
Astrobiologists welcome Cronin's proposal. “I appreciate Lee for developing a biosignal that is based on minimal assumptions about biology,” Wojtek says. "In practice, however, a detector compact enough for an interplanetary mission would probably have to be designed to search for carbon life."
And even if Cronin's method works, no scientist would risk, based on evidence alone, claiming to have found extraterrestrial life, says Kevin Hand of NASA's Jet Propulsion Laboratory, a member of the agency's Europa Lander mission. … This means that future missions will still need to look for multiple biosignals.
Sergey Sysoev