Some of the most anticipated results from the James Webb Space Telescope are those involving the search for signs of life on planets outside the Solar System. It won’t be easy to detect, but a group of researchers suggests at least the best way to try: measuring the amount of methane in the atmosphere of these distant worlds.
The new work, led by Maggie Thompson of the University of California at Santa Cruz, appears in the latest issue of PNAS, a journal of the US National Academy of Sciences, and focuses on the methane concentration profile that would best fit a planet. alive.
Looking at the modern Earth, the gas that, when fired, “screams” the presence of life on the planet the most is oxygen. It makes up 21% of the Earth’s atmosphere and its production is practically exclusively the result of photosynthesis, a biological process. But the role of methane should not be overlooked, which also has a significant presence here and is produced, for the most part, by life. By the way, in the remote terrestrial past, before the advent of photosynthesis, methane was possibly the main atmospheric signal that our planet contained life.
Webb will be able to analyze the atmospheric composition of other worlds as they transit in front of their star and part of their light “grazes” past them, through their gaseous envelope, reaching the telescope with a “signature” of the substances it found. along the way (a measurement that, in scientists, is called transmission spectroscopy).
Special attention is paid to the Trappist-1 system, 40 light-years away. It has seven potentially rocky planets, some of them in the habitable zone (neither too hot, not too cold). Unfortunately, searching for oxygen will be quite difficult with Webb, even in a near-ideal system like this. But methane is another story. “For example, biological methane in Trappist-1e could be detectable with 5 to 10 (observed) transits,” the researchers write. To check.
And attention: even if the detection is positive, you still need to be careful. Because while life is largely responsible for producing methane, there are many other, non-biological ways in which the gas is generated, from the interaction of minerals with water to asteroid impacts.
According to Thompson and colleagues, the best way to determine that the methane on an exoplanet is produced by life is, in addition to measuring the amount, to keep an eye on the presence of carbon dioxide and monoxide. If it is an atmosphere rich in methane and carbon dioxide, but poor in monoxide, the chance that we have found life increases greatly.
As we enter this new era of studying exoplanets, the most anticipated, however, is still the unexpected. Astronomers try to predict what’s next, but they will almost certainly find many surprises ahead.
This column is published on Mondays, in Folha Corrida.
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