This opportunity will come with the launch of James Webb.
In general, the conversation is about the following. After observing Kepler, who died in the Bose, astronomers decided that there are planets the size of the Earth in the habitable zone in our Galaxy of the order of thirty billion. Therefore, the following question arose at full height: how to distinguish potentially inhabited billions from those that are actually inhabited?
Sara Seager of the Massachusetts Institute of Technology (USA), who started digging in this direction, found that the answer to the question posed is more complicated than we would like.
False signals
It would seem that everything is simple: methane, ozone and oxygen (as well as free fluorine, if any) are unlikely to be present in significant quantities in the planet's atmosphere in the habitable zone if there is no life there. Ultraviolet light, oxidation processes of rocks - all this simply leaves no room for these gases.
But here's a caveat: there is methane on Saturn's moon Titan, but there seems to be no stormy life.
And even worse. Sunlight should make acetylene from the molecules of the "titanium" atmosphere - a lot of acetylene. In practice, acetylene is not there, which makes some people say: it means there is life there.
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Ms. Sieger's team tried to calculate what life should be like, which can eat all the acetylene. It turned out that Titan should be covered with an even layer of living creatures, and the thickness of such creatures on average should be equal to one and a half meters. Meanwhile, the sea, rocky surface and various streams are visible on the surface of Titan. On the contrary, there are no titans smeared with a one and a half meter layer. Who Eats Acetylene? Sarah Sieger's team believes that geological activity on the moon of Saturn could do this.
On the other hand, we can not only find traces of life in the atmospheres of other planets when it is not there, but also, on the contrary, fail to notice something similar under our noses.
It's all about our carbon chauvinism, friends. We immediately figure out what kind of gases (on Earth) life is capable of "making", and therefore we believe that aliens, like us, periodically emit methane and everything else. And if the main component of the atmosphere on the planet is hydrogen, and the chemistry of life is generally different?..
Life can be found in worlds with a hydrogen atmosphere
But there is one method. Having driven out many models of atmospheres similar in composition to the gas giants, the researchers found that chloromethane, dimethyl sulfide and nitrogen oxide would be unnatural there. Moreover, any significant alien life in the conditions of the local chemistry is simply obliged to create large quantities of these substances. But their formation as a result of geological activity, especially all at once, is unrealistic.
So far, alas, the composition of the atmospheres is known to us only for a very limited number of giant exoplanets, moreover, young ones, which makes the chances of life there dubious. But, according to the authors' calculations, some luck and commissioning in 2018 of the James Webb space telescope will allow us to see these traces, as well as signs of "more terrestrial" life in the form of oxygen, ozone and methane, on a number of planets.