Astronomers have for the first time detected ingredients in the atmosphere of a super-Earth, an exotic type of exoplanet of which there is no parallel in our solar system: It’s larger than our home but not as large as a gas giant. But 55 Cancri e, as the world is known, wouldn’t make a super holiday destination with a surface temperature of 2000°C, and hydrogen, helium, and hydrogen cyanide to breathe. Ever since the first exoplanets were discovered 2 decades ago, astronomers have been fascinated by super-Earths because we have no model for what they would be like. Although many have been found and they appear to be the most abundant type of exoplanet in the galaxy, current telescopes can tell us little about them. The best current technique is to study the spectrum of light coming from a planet’s parent star as the world passes in front (as shown in the artist’s impression above). Some of the light passes through its atmosphere and key wavelengths of light are absorbed by atoms in the atmosphere leaving a fingerprint of its makeup. The team of astronomers used this technique with observations from the Hubble Space Telescope. As they describe today in The Astrophysical Journal, the scientists scanned Hubble’s Wide Field Camera 3 quickly across the face of the star to capture a number of spectra. Combining these with sophisticated image processing software, they were able pick out several signals. Smaller planets like ours have lost the light elements in their atmospheres, such as hydrogen and helium, but the greater gravity of 55 Cancri e has held onto them. And the presence of hydrogen cyanide suggests an atmosphere rich in carbon, making this super-Earth at least a place very unlike home.
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