It will also require many more observations to be sure that it is a habitable planet.
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. Details of this important discovery are published today in Nature.
Previously, water had only been discovered in the atmospheres of massive super-hot Jupiter-like gas giants.
Known as K2-18 b, the mysterious exoplanet is twice the size of Earth, with eight times its mass, but its atmosphere could help answer burning questions about the possibility of life beyond our solar system. Already though, the K2-18b findings are encouraging more investigations of potentially similar worlds.More news: Eighteen years on, U.S. mourns 9/11 victims
But the density of K2-18 b is what really cements it as a rocky planet.
The planet is a lot closer to its star than Earth is to the Sun, meaning it only takes around 33 days to transit.
The search for alien life may have just received a galactic boost. "It's the best candidate for habitability right now". Using those findings they concluded that K2-18b weighs in at about 8 times Earth's mass.
It could either be a rocky planet with an extended atmosphere or an icy planet with a high concentration of water in its interior.
K2-18b orbits a red dwarf star which has led to speculation that it is exposed to higher levels of radiation than Earth.
That's obviously a huge discrepancy.
"To our great surprise we saw a pretty strong signature of water vapour", said Giovanna Tinetti, a member of the UCL team.More news: Brexit: Nigel Farage election pact proposal rejected by No 10
But scientists everywhere are reported interested in this planet orbiting a small red dwarf star, because it could have water in the atmosphere and temperatures that could sustain liquid water on the surface.
Dr Beth Biller at Edinburgh University's Institute of Astronomy said she believed that evidence of life on a planet around a distant star would eventually be discovered.
The new research, he said, is consistent with his own work.
"It's super exciting to have a first glimpse into the atmosphere of a planet this small", exoplanet researcher Laura Kreidberg told Eos. The data are not precise enough to narrow down this range or to detect other molecules the atmosphere might have, the researchers found.
While the two papers share the general conclusion that K2-18b has water content, there is quite a bit of daylight between their approaches, and their results have different implications for the overall structure of the planet itself. The researchers said they clearly saw the signature for water vapor in the atmosphere when they put the data through algorithms.
Both teams looked at Hubble data to observe the stellar transits of K2-18b as it orbited its host star. "But I don't think it's potentially habitable". If "most planets are born with a large atmosphere of hydrogen and helium that they can't get rid of, it might make it more hard for complex life to develop - we simply don't know enough at this stage", he said. As the water condenses into liquid, the drops would fall toward the core, then revert to gas as the atmospheric pressure increases. When stellar light moves through a planet's atmosphere, it becomes scattered by the presence of different atmospheric elements and compounds. Yet an instrument like the JWST "will provide an order-of-magnitude improvement in measurement precision over Hubble", he says, making it much easier to do detailed studies of any of the 55 habitable-zone exoplanets.More news: Google officially announces its Apple Arcade-rival Play Pass is 'coming soon'
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