Hot and steamy atmosphere detected on Earth-like planet

Ian Sample Science editor
One theory is that GJ 1132b is a “water world” with an atmosphere of hot steam. Photograph: MPIA/PA

Astronomers have found evidence for a hot and steamy atmosphere around an Earth-like planet that circles a red dwarf star in the southern sky.

The discovery marks one of the first times that scientists have spotted an atmosphere around a small, rocky world and brings them one step closer to the goal of finding life elsewhere in the universe.

The planet, which lies 39 light years away in the constellation of Vela, is not considered to be habitable itself, but astronomers regard it as a prime candidate for honing the instruments and techniques they will need to detect the existence of alien life on more hospitable worlds.

When the planet, GJ 1132b, was first discovered in 2015, astronomers had no idea whether or not it had an atmosphere. But in a paper reported in the Astronomical Journal on Thursday, scientists describe how recent observations revealed a shroud of gas around the distant world.

The researchers pored over measurements from the European Southern Observatory in Chile and found that at one wavelength band of light, the planet looked larger than at others, as it crossed the face of its parent star.

“These things don’t pop up in the way you expect,” said John Southworth, an astronomer at Keele University in the UK. “We found evidence for the atmosphere at one wavelength band and that wasn’t what we were expecting.”

The observations point to an atmosphere that is rich in water or methane, but it will take more measurements with other telescopes to identify the chemicals present.

GJ 1132b is about 16% larger than Earth and orbits too close to its star for scientists to consider it habitable. Temperatures on the surface reach more than 250C. “That’s a bit high for life as we know it,” said Southworth. “The planet is significantly hotter and a bit larger than Earth, so one possibility is that it is a ‘water world’ with an atmosphere of hot steam.”

The discovery of the atmosphere will encourage astronomers on the lookout for alien life. Small stars, like the one orbited by GJ 1132b, are extremely common and are known to harbour scores of small, potentially habitable, planets. But the stars can emit huge amounts of x-rays, which are capable of stripping their atmospheres away, spelling disaster for the prospects for life. “What we’ve shown is that a planet similar to Earth can retain an atmosphere for several billion years,” said Southworth.

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