Astronomers have spotted hints of water raining in the atmosphere of a planet beyond the solar system.
The discovery is a rare glimpse of water molecules around a world that is not much bigger than Earth , Named K2-18 b, the planet is 34 parsecs (110 light-years) from Earth in the constellation Leo. Notably, it read in the 'habitable zone' around its star – the distance at which liquid water could exist, making extraterrestrial life possible in its hydrogen-rich atmosphere.
"That's the exciting thing about this planet," says Björn Benneke, a planetary astronomer at the University of Montreal in Canada. He is the lead author of a paper describing the news posted on the arXiv preprint server on September 10 1 .
A competing team of scientists reviews their own analysis of the same planet on September 11 in Nature Astronomy 2 . That paper's lead author, planetary astronomer Angelos Tsairas of the University of College London (UCL), says the discovery is exciting because the planet is just about the diameter of Earth, and because of the small worlds.
Astronomers have previously found water in the atmosphere of gas-giant exoplanets, but studying a distant planet's atmosphere harder as the planet gets smaller.
Benneke and his colleagues decided to look at K2-18.
The scientists analyzed how the color of the star's light changed as it was filtered through the planet's atmosphere. They combined this with data from the Spitzer Space Telescope, which examines more wavelengths of light. The scientists concluded that they were making water vapor in the planet's atmosphere as well as that that vapour was condensing into liquid water.
The UCL team that authored the second paper analyzed the Hubble data from Benneke's group.
It's the first time astronomers have seen a water cycle – change from gas to liquid and back again , The observations had been uploaded to a publicly available archive immediately after being collected.
The UCL researchers came up with three possible explanations for what they were seeing. In the first scenario, the planet has no clouds and 20-50% of its atmosphere is water. 0.01% and 12.5% water.
But the presence of water alone does not mean a planet is a good place to look for life, a point illustrated by one of Earth's closest neighbors, Venus.
K2-18 b might just be unpromising. It's an earth-sized planet in the habitable zone of its star that had water in its atmosphere – but the sun's rays have stripped away much of that water , Hannah Wakeford, a planetary astronomer at the Space Telescope Science Institute in Baltimore, Maryland, says
Still, finding water in the planet's atmosphere is "extremely exciting," says Neale Gibson, at astrophysicist at Trinity College Dublin, "and the fact that two teams find the same result is very encouraging." Future observations, as the James Webb Space Telescope wants to collect after its planned 2021 launch, should help pin down exactly what this distant world is like.