by When it comes to detecting the presence of liquid water on planets outside the solar system, and therefore the conditions necessary for life, the James Webb Space Telescope (JWST) might want to look for what’s missing rather than what’s there. Here’s what that means.
A team of researchers, including scientists from the Massachusetts Institute of Technology (MIT) and the University of Birmingham, suggest that rocky worlds like Earth outside the solar system have less carbon dioxide in their atmospheres than other planets. of the same system, this could be a sign that they host liquid water. And as we know from the formation of life on our own planet and the conditions necessary to support life here, the presence of liquid water is a key indicator of potential habitability.
While the search for key chemical components that indicate the habitability of extrasolar planets, or exoplanets, is barely within reach of current technologies, depleted carbon dioxide is a signal that JWST is now ready to detect.
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“The Holy Grail in exoplanet science is to search for habitable worlds and the presence of life, but all the features that have been talked about so far are beyond the reach of the newest observatories,” said Julien de Wit, a member of the discovery team and assistant professor of planetary sciences at MIT said in a statement. “Now we have a way to find out if there is liquid water on another planet. And it’s something we can get to in the next few years.”
A roadmap to discover life on exoplanets
Today, scientists are very good at using instruments to determine how far a planet is from its host star and therefore whether it is in that star’s “habitable zone,” defined as the region that is neither too hot nor too hot. nor too cold to allow the existence of liquid water.
However, in our own solar system, Earth, Mars, and even Venus are in the habitable zone around the sun. However, currently only one of those planets has the capacity to support life as we know it. That means habitability and preservation of liquid water for exoplanets is not just location, location, location. So currently, scientists have no solid way to confirm whether a planet is habitable or not.
Thinking about Earth, Mars and Venus, as well as the differences between the trio, the team realized that the only one with habitability, Earth, also has a carbon dioxide-depleted atmosphere compared to its nearby neighbors. habitable.
“We assume that these planets were created in a similar way, and if we now see a planet with much less carbon, it must have gone somewhere,” Triaud said. “The only process that could remove that amount of carbon from the atmosphere is a strong water cycle involving oceans of liquid water.”
Over billions of years, our planet’s oceans have been responsible for depleting huge amounts of carbon dioxide from the atmosphere, meaning it now has less than Venus or Mars.
“On Earth, much of the atmospheric carbon dioxide has been sequestered in seawater and solid rock over geological time scales, helping to regulate climate and habitability for billions of years,” says Frieder Klein, co-author of the research and Woods Hole scientist. Oceanographic Institution (WHOI), he said in the statement.
That led the team to think that a similar depletion of carbon dioxide in an exoplanet’s atmosphere could also indicate the presence of a liquid ocean.
Performing a search with these parameters would be best suited for “small” planetary systems that, like the solar system, host multiple rocky or terrestrial worlds of similar sizes orbiting their star at similar distances.
The first step in the team’s suggested research is to look for carbon dioxide and use it as an indicator that the target exoplanets have an atmosphere. Once it is determined that several planets in a single system have atmospheres, the next step would be to determine how much carbon dioxide is in the atmospheres.
This should reveal whether one or more of the planets has significantly less carbon dioxide than the others, indicating that it probably has liquid water oceans and could therefore be habitable.
Of course, this method involves more than simply comparing carbon dioxide abundance. “Habitability” is not the same as “inhabited.” To check if life can really exist on an exoplanet characterized by a lack of carbon dioxide, the team suggests looking for another molecule: ozone.
Made up of three oxygen atoms, ozone is a molecule created when life forms such as plants and microorganisms draw carbon dioxide from Earth’s atmosphere and then emit oxygen molecules that are impacted by sunlight. Ozone is a good indicator of these processes on alien worlds because it is easier to detect in the atmosphere of distant exoplanets than oxygen itself.
The team says that if a planet’s atmosphere shows signs of depleted carbon dioxide along with an abundance of ozone, then it could well be habitable and inhabited.
“If we see ozone, there is a good chance that it is related to the carbon dioxide that is consumed by life,” Triaud added. “And if it is life, it is glorious life. It wouldn’t just be a few bacteria. It would be planetary-scale biomass capable of processing an enormous amount of carbon and interacting with it.”
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— Two potentially habitable Earth-like worlds orbit a star in our cosmic backyard
— 2 ‘super-Earth’ exoplanets detected in the habitable zone of a nearby star
Researchers believe that JWST is already capable of measuring the abundance of carbon dioxide and ozone in multiplanetary near-Earth systems.
This includes the TRAPPIST-1 system, located 40 light-years away, which is home to seven Earth-like planets, several of which are in the habitable zone of their cold star.
“TRAPPIST-1 is one of the few systems where we could perform terrestrial atmospheric studies with JWST,” de Wit concluded. “We now have a roadmap to find habitable planets. If we all work together, paradigm-shifting discoveries can be made in the coming years.”
The team’s research was published December 28 in the journal Nature Astronomy.
