Super soil with hydrogen cyanide atmosphere

Near Exoplanet 55 Cancri e is even more exotic than previously thought

Super Earth 55 Cancri e orbits its sun-like star very close. © ESA / Hubble, M. Grain knife
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Carbon-rich and quite toxic: astronomers have for the first time gained insight into the gas envelope of the nearby super-earth 55 Cancri e. Their spectral analyzes reveal that the atmosphere does not contain any water vapor, but it contains all the more hydrogen, helium and copious toxic hydrogen cyanide gas. This unusual find suggests that 55 Cancri e is indeed very carbon rich and even more exotic than thought.

The Super Earth 55 Cancri e, which is only about 41 light-years away, is a superlative planet: Earth's eight-fold super-Earth is so dense that astronomers speculate that this planet may be partially made of diamond and graphite. In addition, 55 Cancri e circles its sun-like star extremely narrow and fast - a year only lasts 18 hours. As a result, the surface is on average 2, 000 degrees hot. However, the temperature fluctuates so strongly that researchers suspect a strong volcanic activity.

First spectral view into the gas envelope

Now the Hubble Space Telescope is delivering new surprises from this near super Earth. With him succeeded Angelos Tsiaras of University College London and his colleagues to determine the composition of the atmosphere of 55 Cancri e. "For the first time, we've captured the spectral fingerprints of the gases found in the atmosphere of a super-earth, " says Tsiaras.

For the measurement, the astronomers with the wide-field camera 3 of the telescope very quickly crossed the star and the super-earth. In this way, they prevented the bright light of the star from overburdening the optics, yet were able to capture spectra of starlight in the infrared range. Because this light also shines through the planet's gas envelope, its spectral lines provide information about the elements present there.

55 Cancrei e is the first super-earth whose atmosphere astronomers have analyzed. ESA / Hubble, M. Grain knife

Hydrogen, helium and blue acid

The result: The atmosphere of 55 Cancri e consists for the most part of very light elements, as the researchers report. "This suggests that the planet has retained a significant amount of hydrogen and helium from the primeval nebula from which it originated, " says Tsiaras. On the other hand, water vapor does not appear to be present in the gas well of this super-earth, and no spectral signal could be found from it. display

However, two other spectral lines of the gas well were unusual, since they could be derived from hydrogen cyanide (HCN) Blueşuregas. "If confirmed, the consequences for the chemistry of 55 cancers would be significant, " the researchers emphasize. Because this compound is highly toxic for us, but it is considered as an indicator of atmospheres that are dominated by carbon compounds.

Unusually rich in carbon

"This result indicates that this super-earth has a carbon-rich environment that is even more unusual than previously thought, " say Tsiaras and his colleagues. At the same time, this possible dominance of carbon in the gas well fits well with the theory of 55 Cancri e as the "diamond planet". Because if its surface mainly consists of carbon compounds, it is obvious that the gas well shows corresponding traces of this element.

"These data give us a first glimpse into the atmosphere of a super-earth and give us clues as to how this planet is designed, how it could have formed and developed, " says Tsiaras. "This has great significance for 55 Cancri e, but also other super-earths." (Astrophysical Journal, in press; arXiv: 1511.08901)

(Europlanet Media Center, 17.02.2016 - NPO)