Astronomers from the University of Cambridge said they have observed a distant planet that could be entirely covered in a deep water ocean using Nasa’s James Webb space telescope (JWST). They said the findings revealed water vapour and chemical signatures of methane and carbon dioxide in the atmosphere of the exoplanet.
The planet, TOI-270 d, is twice Earth’s radius and about 70 light years away. The researchers said the planet’s chemical composition is consistent with a water world where the ocean would span the entire surface and a hydrogen-rich atmosphere.
The researchers, however, have questioned the habitability of the planet. “The ocean could be upwards of 100°C or more, but it’s not clear if it would be habitable,” Prof Nikku Madhusudhan, who led the analysis said, according to The Guardian.
He also said that at high atmospheric pressure, an ocean this hot could still be liquid.
A Canadian team, however, disputed the findings mentioned above which were published in the journal Astronomy and Astrophysics Letters.
They identified identical atmospheric chemicals but argued that the planet’s temperature would reach an extreme 4,000°C, making liquid water unlikely. Instead, they proposed a rocky surface enveloped by an intensely dense atmosphere composed of hydrogen and water vapour.
No matter which observation stands, these findings highlight the remarkable discoveries regarding planets outside our solar system that the James Webb telescope is making as it helps astronomers to paint an image regarding the surface conditions of those plants and assess the potential for sustaining life.
The indication of an ocean on TOI-270 d stems from the absence of ammonia, a compound expected in a hydrogen-rich atmosphere according to basic chemistry. However, ammonia is readily soluble in water, leading to its depletion in the atmosphere if an ocean exists beneath the surface.
“One interpretation is that this is a so-called ‘hycean’ world – with a water ocean under a hydrogen-rich atmosphere,” Madhusudhan was quoted as saying by The Guardian.
TOI-270 d experiences vastly different conditions compared to Earth. Being tidally locked, one side of the planet always faces its star, while the other remains in constant darkness. This results in a dramatic temperature difference between the two sides.
“The ocean would be extremely hot on the day side. The night side could potentially host habitable conditions,” Madhushudhan further added.
TOI-270 d’s atmosphere would be extremely dense, exerting pressure tens or hundreds of times greater than that experienced at Earth’s surface. Steam would likely rise from the ocean due to the intense heat. The ocean itself could be incredibly deep, spanning tens to hundreds of kilometers, with a seabed made of high-pressure ice. Beneath this ice layer lies a rocky core.
Prof Björn Benneke, of the University of Montreal, has questioned the “hycean world” hypothesis. “The temperature in our view is too warm for water to be liquid. It’s almost like a thick, hot fluid,” Benneke was quoted as saying by The Guardian.
Benneke also noted that the atmosphere seemed to have significant levels of water vapour, suggesting that the presence of an ocean may not be feasible due to excessive moisture. Surface temperatures, estimated by Benneke to reach 4000°C, would result in water existing in a supercritical state, blurring the boundary between liquid and gas phases.
“We need to be extremely careful about how we communicate findings on this kind of object. It’s easy for the public to jump on to the idea that we’re finding life already,” Benneke further added.
Both team did detect carbon disulphide, which is linked to biological processes on Earth but they did not find the sign of another biosignature molecule, dimethyl sulphide (DMS).
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