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Image: 55 Cancri e
An artist’s impression shows the super-Earth 55 Cancri e in front of its parent star. The star is slightly smaller, cooler and less massive than our sun. (Credit: M. Kornmesser / ESA / Hubble)

For the first time, astronomers have conducted a spectral analysis of a distant super-Earth’s atmosphere – and the results show it would be a hellish place to visit.

We already knew that about 55 Cancri e, which is about 40 light-years from Earth in the constellation Cancer. It circles its parent star once every 18 hours, in an orbit so close that its surface temperature is 3,900 degrees Fahrenheit (2,100 degrees Celsius). The world, which is also known as Planet Janssen, is eight times as massive as Earth and has been nicknamed the diamond planet due to its carbon content.

Now we know the planet’s air would be poisonous, even if it we could cool it down.

A research team led by astronomers from University College London used the Hubble Space Telescope’s Wide Field Camera 3 to study variations in the spectral signature of light coming from 55 Cancri e’s parent star. By carefully analyzing the patterns in those spectral variations, and matching them up with the planet’s transit across the sun’s disk, the researchers were able to pull out the signature of the planet’s atmosphere from the starlight.

The result? 55 Cancri e’s atmosphere is dominated by hydrogen and helium.

“This is a very exciting result, because it’s the first time that we have been able to find the spectral fingerprints that show the gases present in the atmosphere of a super-Earth,” Angelos Tsiaras, a Ph.D. student at UCL, said in a news release. “The observations of 55 Cancri e’s atmosphere suggest that the planet has managed to cling on to a significant amount of hydrogen and helium from the nebula from which it originally formed.”

The findings have been accepted for publication in the Astrophysical Journal. Other astronomers have observed super-Earths closely enough to produce information about their atmospheres, including findings that suggest there are clouds in those atmospheres. But the European Space Agency’s Hubble team says those earlier studies weren’t able to get the spectral data that the UCL-led team got.

Previous analyses of exoplanetary atmosphere have sometimes turned up evidence of water vapor. That’s not the case here. However, there are hints of another exotic gas, hydrogen cyanide, which is typically associated with carbon-rich environments.

“If the presence of hydrogen cyanide and other molecules is confirmed in a few years time by the next generation of infrared telescopes, it would support the theory that this planet is indeed carbon-rich and a very exotic place,” UCL astronomer Jonathan Tennyson said. “Although hydrogen cyanide, or prussic acid, is highly poisonous, so it is perhaps not a planet I would like to live on!”

Some astronomers have proposed that super-Earths, which are defined as planets with a mass one to 10 times greater than Earth’s, would be superior places for life to develop. The latest results show that’s not necessarily so.

In addition to Tsiaras and Tennyson, the authors of “Detection of an Atmosphere Around the Surface of Super-Earth 55 Cancri b” include M. Rocchetto, I. P. Waldmann, O. Venot, R. Varley, G. Morello, G. Tinetti, E. J. Barton and S. N. Yurchenko.

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