Astronomers find new way to detect oceans of water and extraterrestrial life on rocky exoplanets| Trending Viral hub

Planets that are too close to their star are too hot (like Venus), those that are too far away are too cold (like Mars), while planets in the habitable zone are perfect. While many efforts have been made to identify planets in the theoretical habitable zones of their stars, until now there was no way to know if they actually have liquid water. Now, astronomers from the University of Birmingham, MIT and elsewhere have shown that if an exoplanet has a reduced amount of carbon dioxide in its atmosphere compared to neighboring planets, it suggests that there is liquid water on that planet’s surface.

An artist's impression of the super-Earth planet Ross 508b.  Image credit: Sci.News.

An artist’s impression of the super-Earth planet Ross 508b. Image credit: Sci.News.

So far astronomers have detected more than 5,200 extrasolar worlds. With today’s telescopes, they can directly measure a planet’s distance from its star and the time it takes to complete one orbit.

Those measurements can help scientists infer whether a planet is within a habitable zone.

But there has been no way to directly confirm whether a planet is actually habitable, meaning that liquid water exists on its surface.

Throughout our own Solar System, astronomers can detect the presence of liquid oceans by observing flares: flashes of sunlight reflecting off liquid surfaces.

These flares, or specular reflections, have been observed, for example, on Saturn’s largest moon Titan, helping to confirm the moon’s large lakes.

However, detecting a similar glow on distant planets is beyond the reach of current technologies.

But MIT astronomer Julien de Wit, University of Birmingham astronomer Amaury Triaud and their colleagues realized that there is another habitable feature close to home that could be detectable on distant worlds.

“We came up with an idea by looking at what is happening with the terrestrial planets in our own system,” Dr. Triaud said.

Venus, Earth and Mars share similarities: all three are rocky and inhabit a relatively temperate region relative to the Sun.

Earth is the only planet of the trio that currently hosts liquid water. And the researchers noted another obvious distinction: Earth has significantly less carbon dioxide in its atmosphere.

“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,” Dr. 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.”

In fact, Earth’s oceans have played an important and sustained role in absorbing carbon dioxide.

Over hundreds of millions of years, the oceans have absorbed an enormous amount of carbon dioxide, almost equal to the amount that persists today in the atmosphere of Venus.

This planetary-scale effect has left Earth’s atmosphere significantly depleted of carbon dioxide compared to its planetary neighbors.

“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,” said Dr. Frieder Klein, a researcher at the Woods Hole Oceanographic Institution. .

Astronomers reasoned that if a similar depletion of carbon dioxide were detected on a distant planet, compared to its neighbors, this would be a reliable sign of liquid oceans and life on its surface.

“After extensively reviewing the literature from many fields, from biology to chemistry and even carbon sequestration in the context of climate change, we believe that, in fact, if we detect carbon depletion, there is a good chance that it will be a strong sign of liquid water and/or life,” said Dr. de Wit.

In the study, the researchers lay out a strategy to detect habitable planets by searching for a signal of depleted carbon dioxide.

Such a search would work best for “peas in a pod” type systems, in which multiple terrestrial planets, all about the same size, orbit relatively close to each other, similar to our own Solar System.

The first step scientists propose is to confirm that planets have atmospheres, simply by looking for the presence of carbon dioxide, which is expected to dominate most planetary atmospheres.

“Carbon dioxide is a very strong infrared absorber and can be easily detected in the atmospheres of exoplanets,” said Dr de Wit.

“A carbon dioxide signal may reveal the presence of exoplanet atmospheres.”

Once astronomers determine that several planets in a system host atmospheres, they can move on to measuring their carbon dioxide content, to see if one planet has significantly less than the others.

If so, the planet is likely habitable, meaning it hosts significant masses of liquid water on its surface.

But habitable conditions do not necessarily mean that a planet is inhabited. To see if life could really exist, the authors propose that astronomers look for another feature in a planet’s atmosphere: ozone.

On Earth, plants and some microbes help extract carbon dioxide, although not as much as the oceans. However, as part of this process, life forms emit oxygen, which reacts with photons from the Sun to transform into ozone, a molecule much easier to detect than oxygen itself.

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

“If we see ozone, there is a good chance that it is related to carbon dioxide that is consumed by life,” Dr. Triaud said.

“And if it is life, it is glorious life. It wouldn’t just be a few bacteria. “It would be a biomass on a planetary scale capable of processing an enormous amount of carbon and interacting with it.”

The team estimates that the NASA/ESA/CSA James Webb Space Telescope could measure carbon dioxide, and possibly ozone, in nearby multiplanetary systems like TRAPPIST-1, a seven-planet system orbiting a bright star, just 40 degrees away. light years from Earth.

“TRAPPIST-1 is one of the few systems where we could perform terrestrial atmospheric studies with Webb,” said Dr. de Wit.

“We now have a roadmap to find habitable planets. If we all work together, in the coming years we will be able to make discoveries that change paradigms.”

He study was published in the magazine Nature Astronomy.


AHMJ Triad et al. Atmospheric carbon depletion as a marker of ocean water and biomass on temperate terrestrial exoplanets. Nat Astron, published online December 28, 2023; doi:10.1038/s41550-023-02157-9

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