Faraway planet 'may be covered in deep, boiling ocean'

Astronomers have observed a distant planet that could be entirely covered in a deep water ocean, in findings that advance the search for habitable conditions beyond Earth.

- Hannah Devlin

The observations, by Nasa's James Webb space telescope (JWST), revealed water vapour and chemical signatures of methane and carbon dioxide in the atmosphere of the exoplanet, which is twice Earth's radius and about 70 light years away. This chemical mix is consistent with a water world where the ocean would span the entire surface, and a hydrogen-rich atmosphere, according to researchers from the University of Cambridge, although they do not envisage a balmy, inviting seascape.

Prof Nikku Madhusudhan, who led the analysis, said: "The ocean could be upwards of 100 degrees [Celsius] or more." At high atmospheric pressure, an ocean this hot could still be liquid, "but it's not clear if it would be habitable", he added.

This interpretation is favoured in a paper published in the journal Astronomy and Astrophysics Letters, but is disputed by a Canadian team that made additional observations of the same exoplanet, which is known as TOI-270 d. They detected the same atmospheric chemicals but argue the planet would to be too hot for liquid water-possibly 4,000C - and instead would feature a rocky surface topped by an extremely dense atmosphere of hydrogen and water vapour.