The low carbon content in planetary atmospheres detected by the James Webb Space Telescope may be a sign of habitability. Scientists from the Massachusetts Institute of Technology, the University of Birmingham and elsewhere say astronomers’ best chance of finding liquid water and even life on other planets is to look for the absence, not the presence, of a chemical feature in their atmospheres.

Researchers suggest that if a terrestrial planet has significantly less carbon dioxide in its atmosphere than other planets in the same system, this could be a sign of liquid water and possibly life on that planet’s surface.

This new signature is at most within the field of view of NASA’s James Webb Space Telescope (JWST). Although scientists suggest other signs of habitability, these characteristics are difficult, if not impossible, to measure with modern technology. The team says this new feature, relatively depleted carbon dioxide, is the only sign of habitability that can currently be detected.

“The holy grail of exoplanet science is the search for habitable worlds and the existence of life, but all the features discussed so far have been beyond the reach of the latest observatories,” says Julien de Wit, associate professor of planetary science. sciences at MIT. “We now have a way to find out if there is liquid water on another planet. “This is where we can reach in the next few years.”

The team’s findings were recently published. Nature Astronomy. De Wit co-led the study with the Amory Trio from the University of Birmingham in England. Co-authors from MIT include Benjamin Rackham, Prajwal Niraula, Ana Glidden, Oliver Jaguz, Matej Peč, Janusz Petkowski, and Sara Seeger, as well as Frieder Klein from Woods Hole Oceanographic Institution (WHOI) and Martin Turbet from Ecole Polytechnique. . in France and Frank Celsis of the Bordeaux Astrophysics Laboratory.

Beyond Trembling

So far, astronomers have discovered more than 5,200 worlds outside our solar system. With the help of modern telescopes, astronomers can directly measure a planet’s distance from its star and the time it takes to complete its orbit. These measurements can help scientists infer whether a planet is in the habitable zone. But there was no way to directly confirm whether the planet was actually habitable, that is, whether there was liquid water on its surface.

Scientists can detect the presence of liquid oceans throughout our solar system by observing “sparkles,” which are flashes of sunlight reflected from liquid surfaces. These reflections, or specular reflections, have been observed, for example, on Saturn’s largest moon Titan, helping to confirm the existence of large lakes on the moon.

However, detecting such vibrations on distant planets is not possible with the help of modern technologies. But de Wit and his colleagues realized there was another habitable element closer to home that could be discovered on distant worlds.

“We came up with the idea while watching what was happening on the terrestrial planets in our system,” says Trio.

Venus, Earth, and Mars are similar in that all three are rocky and occupy a relatively temperate region relative to the Sun. The only planet of this trio that currently has liquid water is Earth. The team noted another obvious difference: There is much less carbon dioxide in Earth’s atmosphere.

“We assume these planets were created in a similar way, and if we now see a planet with a much lower carbon content, it must have gone somewhere,” Trio says. “The only process that could remove this much carbon from the atmosphere is a powerful water cycle that includes oceans of liquid water.”

In fact, Earth’s oceans play a significant and ongoing role in absorbing carbon dioxide. Over hundreds of millions of years, the oceans absorbed an amount of carbon dioxide nearly equal to the amount stored in Venus’ atmosphere today. This planetary-scale impact has resulted in Earth’s atmosphere not consuming significantly carbon dioxide compared to its planetary neighbors.

“On Earth, most of the carbon dioxide in the atmosphere has been absorbed by seawater and solid rocks over geological time, helping to regulate climate and habitability over billions of years,” says Frieder Klein, one of the authors of the study.

The team reasoned that if a similar decrease in carbon dioxide was detected on a distant planet relative to its neighbors, it would be a strong signal of liquid oceans and life on its surface.

“After carefully examining the literature in many fields, from biology to chemistry and even carbon sequestration in the context of climate change, we believe that if we find carbon depletion, it is highly likely to be a strong sign of the release of liquid water and carbon/or life” – says de Wit.

Road map to life

In their study, the team outlines a strategy to detect habitable planets by looking for traces of depleted carbon dioxide. Such a search would work best for “peas in a pod” systems, similar to our solar system, where several terrestrial planets of roughly the same size orbit relatively close together. The first step, the team suggests, is to confirm that planets have atmospheres by looking for the presence of carbon dioxide, which is expected to dominate the atmospheres of most planets.

“Carbon dioxide absorbs infrared radiation very strongly and can be easily detected in the atmospheres of exoplanets,” explains De Wit. “Carbon dioxide signal could reveal the presence of an exoplanet’s atmosphere.”

Once astronomers determine that several planets in a system have atmospheres, they can move on to measuring carbon dioxide content to see if one planet has significantly less atmosphere than the others. If this is the case, the planet is likely habitable, meaning it has significant bodies of liquid water on its surface.

However, habitable conditions do not necessarily mean that the planet is inhabited. To test whether life really exists, the team suggests astronomers look for another feature of the planet’s atmosphere: ozone.

Researchers state that on Earth, plants and some microbes help absorb carbon dioxide, although not as much as the oceans. But as part of this process, life forms release oxygen, which reacts with photons from the sun to become ozone, a molecule that is much easier to detect than oxygen itself.

If a planet’s atmosphere shows signs of both ozone and depleted carbon dioxide, that planet is likely a habitable and habitable world, researchers say.

“If we see ozone, there’s a good chance it’s related to carbon dioxide being consumed by life,” Trio says. “And if that’s life, it’s amazing life. It wouldn’t just be a few bacteria. It would be a planetary-scale biomass that can process and interact with enormous amounts of carbon.”

The team predicts that NASA’s James Webb Space Telescope will be able to measure carbon dioxide and possibly ozone in nearby multi-planet systems such as TRAPPIST-1, a seven-planet system orbiting a bright star just 40 light-years away. from the world

“TRAPPIST-1 is one of the few systems where we can study the Earth’s atmosphere with JWST,” says de Wit. “We now have a roadmap to find habitable planets. If we all work together, paradigm-shifting discoveries could be made in the next few years.”