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Nasa’s Webb telescope spots intriguing distant planet with signs of water vapour atmosphere

‘Water vapour in an atmosphere on a hot rocky planet would represent a major breakthrough’

Vishwam Sankaran
Thursday 04 May 2023 08:05 BST
Related video: Astronomers Capture the Moment a Star Expands and Eats One of Its Orbiting Planets

Nasa’s James Webb Space Telescope has helped astronomers find a strange faraway rocky planet that shows hints of a water vapour-rich atmosphere despite its proximity to its star.

Researchers, including those from Nasa’s Goddard space center, say the exoplanet known as GJ 486 b is too close to its star to be within the habitable zone, with a surface temperature of about 800 degrees Fahrenheit.

The planet, located about 26 light-years away in the constellation Virgo, is about 30 per cent larger than Earth and nearly three times as massive, meaning it is a rocky world with stronger gravity than Earth.

GJ 486 b orbits a red dwarf star, completing a revolution in just under 1.5 Earth days, and is likely tidally locked, with a permanent day side and a permanent night side.

However, the signs of water vapour associated with the planet could indicate it has an atmosphere despite its scorching temperature and close proximity to its star, the study, published in the journal The Astrophysical Journal Letters, noted.

Previous studies have shown that red dwarf stars are cool enough that planets near them have a tight orbit to stay warm enough to potentially host liquid water to create a habitable zone for life.

While water vapour has been seen on gaseous exoplanets orbiting such stars before, no atmosphere has been definitely detected around a rocky exoplanet.

Researchers however caution following the new discovery that the water vapour could be on the star itself, and not from the planet at all.

“Water vapour in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science. But we must be careful and make sure that the star is not the culprit,” study author Kevin Stevenson from the Johns Hopkins University in the US said.

“We see a signal, and it’s almost certainly due to water. But we can’t tell yet if that water is part of the planet’s atmosphere, meaning the planet has an atmosphere, or if we’re just seeing a water signature coming from the star,” study lead author Sarah Moran from the University of Arizona in Tucson explained.

Scientists have spotted the star transiting its star, crossing in front of the red dwarf from the Earth’s point of view.

If the planet has an atmosphere, then when it transits, starlight would filter through those gasses, imprinting fingerprints in the light that allow astronomers to decode its composition.

Decoding the chemical makeup of the planet during its transits, astronomers concluded that the most likely source of the signal from the planet was water vapour.

While the water vapour could potentially indicate the presence of an atmosphere, researchers say the signals may likely be coming from the star.

There have also been similar reports of water vapour in our own Sun existing sometimes in sunspots.

Since GJ 486 b’s host star is much cooler than the Sun, scientists suspect even more water vapour may concentrate within its starspots.

This may have created a signal mimicking a planetary atmosphere, they say.

As water vapour atmosphere could gradually erode due to heating from the star, even if an atmosphere were present, researchers say it would need to be constantly replenished by volcanoes from the planet’s interior.

They say additional observations are needed to narrow down how much water is present if there is conclusive evidence of one.

Researchers hope to study data from multiple Webb instruments to conclusively determine the presence of water vapour.

“It’s joining multiple instruments together that will really pin down whether or not this planet has an atmosphere,” Dr Stevenson said.

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