Using the NASA/ESA Hubble Space Telescope, European astronomers have been able to examine the atmosphere of the extrasolar planet 55 Cancri e in unprecedented detail.
An artist’s impression of the exoplanet 55 Cancri e. According to Tsiaras and co-authors, the atmosphere of this planet consists mainly of hydrogen and helium. Image credit: NASA / ESA / Hubble Space Telescope.
55 Cancri e has a radius twice Earth’s, and a mass eight times greater, making it a so-called super-Earth.
This exoplanet was discovered in August 30, 2004, and is one of five planets orbiting the Sun-like star 55 Cancri A that is located 40 light-years away yet visible to the naked eye in the constellation of Cancer.
55 Cancri e orbits its host star at a distance of 0.015 AU – about 25 times closer than Mercury is to our Sun – every 18 hours.
The planet is also tidally locked, meaning that it doesn’t rotate like Earth does – instead there is a permanent ‘day’ side and a ‘night’ side.
Now, using observations made with the Wide Field Camera 3 (WFC3) on board the NASA/ESA Hubble Space Telescope, a team of astronomers has been able to analyze the atmosphere of this exoplanet. The results revealed the presence of hydrogen and helium, but no water vapor.
“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,” said team member Angelos Tsiaras of University College London, lead author of a paper accepted for publication in the Astrophysical Journal (arXiv.org preprint).
“Our 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 formed.”
Hubble’s WFC3 camera has already been used to probe the atmosphere of two super-Earths, but no spectral features were found in these previous studies.
New observations of 55 Cancri e were made by scanning WFC3 very quickly across the star to create a number of spectra.
By combining these observations and processing through a computer ‘pipeline’ series of analysis, Tsiaras and his colleagues were able to retrieve the spectral fingerprints of 55 Cancri e embedded in the starlight.
“This result gives a first insight into the atmosphere of a super-Earth,” said co-author Prof. Giovanna Tinetti, also from University College London.
“We now have clues as to what the planet is currently like, how it might have formed and evolved, and this has important implications for 55 Cancri e and other super-Earths.”
The new data also hinted at a signature for hydrogen cyanide (HCN), a marker for carbon-rich atmospheres.
“Such an amount of hydrogen cyanide would indicate an atmosphere with a very high ratio of carbon to oxygen,” said co-author Dr Olivia Venot of KU Leuven.
“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,” said study senior author Prof. Jonathan Tennyson, of University College London.
“Although, hydrogen cyanide or prussic acid is highly poisonous, so it is perhaps not a planet I would like to live on,” he added.
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A. Tsiaras et al. 2016. Detection of an atmosphere around the super-Earth 55 Cancri e. ApJ, accepted for publication; arXiv: 1511.08901
