Water found at exoplanet with right temperatures for life

12 Septembre, 2019, 07:39 | Auteur: Therese Cote
  • ESA  Hubble shows the K2-18b super-Earth the only super Earth exoplanet known to host both water and temperatures that could support life. | AFP

Whether or not life could exist on K2-18b is unknown, but the discovery of water vapor makes it a promising target for future observations-especially for the James Webb Telescope (JWST), which is now scheduled for launch in 2021 and will be able to detect "biosignatures"-and is possibly an indication that life is present".

K2-18b will surely be receiving more attention from astronomers around the world, not only with existing telescopes but with next-generation ones, including NASA's James Webb Space Telescope, tentatively set for launch in 2021; and the European Space Agency's ARIEL space telescope, specifically created to study the atmosphere of exoplanets, and targeted for a 2028 launch. "Over 4,000 exoplanets have been detected but we don't know much about their composition and nature".

"Finding water in a potentially habitable world other than Earth is incredibly exciting".

The University College London scientists say it's the only exoplanet known so far to have both water and temperatures needed for life, making it a prime candidate for potential life. "But if we find all that around a planet around a distant star we have to be cautious about saying that it supports life", she said. "The only question that we're trying to ask here, and we're pushing forward, is the question of habitability".

The discovery, published today in Nature Astronomy, is the first successful atmospheric detection for an exoplanet orbiting in its star's "habitable zone", at a distance where water can exist in liquid form. "We don't know any other planet with the right temperature that has water in its atmosphere", Tsiaras told the Guardian.

They found the unmistakable signature of water vapour.

"With the current data, we can only detect the existence of an atmosphere and the existence of water", Tsiaris said. Further studies are required to estimate cloud coverage and the percentage of atmospheric water present. Using those findings they concluded that K2-18b weighs in at about 8 times Earth's mass. Because it is so much closer to its parent star, it orbits quite quickly: one year on K2-18 b is equal to just 33 days here on Earth. Its star, a red dwarf, is considerably smaller and cooler than our sun, a yellow dwarf, and its atmosphere is also different than ours. So, if you were standing on the surface of the planet under clear skies, you would see a red star overhead instead of our yellowish-orange sun (though, because of the high gravity and higher UV radiation on the surface of this exoplanet, it might not be possible or safe to walk around). Astronomers detect the atmospheres by analyzing light from the host star as the exoplanet passes in front of it, or transits.

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There was also evidence of hydrogen and helium as well. "We really want to understand this type of planet, and we're hoping the atmospheres will provide some clue as to what they are".

"These are, statistically, equally likely, given the data", Ingo Waldmann, one of the authors of this new study, said in the news conference.

Tsiaras and his team think the planet is likely a rocky "super-Earth" in possession of an atmosphere that's either very water dominant, heavily mixed with a transparent gas like nitrogen, or features significant cloud formation.

"It's a step in the right direction", Sara Seager, a professor of planetary science, physics and aerospace engineering at the Massachusetts Institute of Technology who was not involved with this study, told Space.com. Despite this abundance, probing the conditions and atmospheric properties on any of these habitable-zone planets is extremely hard and has remained elusive to date ... What's it made of? Their model, which incorporates the Kepler and Spitzer data, suggests that K2-18b is a "mini-Neptune" consisting of a small icy or rocky core wrapped in a gaseous envelope.

To qualify as a super-Earth, a planet needs to have a mass that is between those of Earth and Neptune.

All this makes a pretty compelling case for pointing the next generation of wider wavelength instruments - such as the James Webb Space Telescope and the Atmospheric Remote-sensing Infrared Exoplanet Large - in the planet's direction.



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