by Astronomers have discovered a distant planet that may be completely covered in deep oceans, in findings that advance the search for habitable conditions beyond Earth.
The observations, made by NASA’s James Webb Space Telescope (JWST), showed water vapor and the chemical signatures of methane and carbon dioxide in the atmosphere of the exoplanet, which is twice the radius of Earth and about 70 light-years away. This chemical combination is consistent with a water world where the ocean would cover the entire surface, and an atmosphere rich in hydrogen, according to researchers from the University of Cambridge, although they do not imagine a balmy seascape, inviting it.
“The ocean could be over 100 degrees [Celsius] or more,” said Professor Nikku Madhusudhan, who led the analysis. At high atmospheric pressure, an ocean this hot could still be liquid, “but it’s not clear if it would be habitable,” he said.
This interpretation is favored in a paper published in the journal Astronomy and Astrophysics Letters, but disputed by a Canadian team that made additional observations of the same exoplanet, known as TOI-270 d. They detected the same atmospheric chemicals but argue that the planet would be too hot for liquid water – perhaps 4,000C – and would instead have a rocky surface topped by an extremely dense atmosphere of hydrogen and water vapour.
Whichever view wins, these latest observations show the amazing insight James Webb is providing into the nature of the planets outside our solar system. The telescope captures the starlight filtered through the atmospheres of the orbiting planets to provide detailed breakdowns of the chemical elements present. From this, astronomers can build a picture of conditions on a planet’s surface – and the likelihood that life will be able to survive there.
The evidence for a TOI-270d ocean is based on the absence of ammonia, which fundamental chemistry predicts should occur naturally in a hydrogen-rich atmosphere. But ammonia is very soluble in water so it would be depleted in the atmosphere if there were an ocean below. “One interpretation is that this is a so-called ‘hycean’ world – with an ocean of water under a hydrogen-rich atmosphere,” Madhusudhan said.
Conditions would be very different from those on earth. TOI-270 d is tidally locked, meaning that one side is permanently facing its star and the other is stuck in eternal darkness, creating a stark temperature contrast.
“The ocean would be extremely warm on the day side. Conditions may be habitable on the night side,” said Madhusudhan. But there would be a pressurized atmosphere, thousands or hundreds of times the pressure at the Earth’s surface, and steam rolling off the ocean. The waters are likely to reach a depth of between ten and hundreds of kilometres, with a high-pressure ice bed, and a rocky core below that.
Professor Björn Benneke, from the University of Montreal, has made additional observations on the planet and questions the “hycean world” hypothesis. “Our view is that the temperature is too hot for water to be a liquid,” he said, adding that there appeared to be significant amounts of water vapor in the atmosphere – too much for an ocean to form. to be there At the surface, the temperature could reach 4000C, according to Benneke, with the water in a supercritical state, where the distinction between liquid and gas becomes blurred. “It’s almost like a thick, hot fluid,” he said.
Both teams found carbon disulfide, which is linked to biological processes on Earth, but can also be produced by other sources. However, there was no sign of another biomarker molecule, dimethyl sulfide (DMS).
“We cannot bind [carbon disulphide] with biological activity,” said Madhusudhan. “In a hydrogen-rich atmosphere, it’s relatively easy to do. But if we are able to measure the unique molecule it is promising that we will be able to measure habitable planets in the future.
“We have to be very careful about how we communicate results on this type of object,” he said. “It’s easy for the public to jump to the belief that we’re already finding life.”
Dr Jo Barstow, an astronomer at the Open University who was not involved in the latest work, said: “The spectra of these minor planets by JWST are very exciting because these are brand new environments for which we have no solar system equivalent.”
Barstow also said that additional observations of the abundance of water vapor in the atmosphere would help clarify the likelihood of an ocean. “It’s really interesting and really nice that two teams have looked at the same data set and created the same chemical composition,” she said.
