The first successful detection of gases in the atmosphere of a super-Earth reveals the presence of hydrogen and helium, but no water vapour. The exotic exoplanet, 55 Cancri e, is over eight times the mass of Earth and has previously been dubbed the ‘diamond planet’ because models based on its mass and radius have led some astronomers to speculate that its interior is carbon-rich. Now, using new processing techniques on data from the NASA/ESA Hubble Space Telescope, a UCL-led team of European researchers has been able to examine the atmosphere of 55 Cancri e, also known as ‘Janssen’, in unprecedented detail. The results have been published in the Astrophysical Journal.
“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 Angelos Tsiaras, a PhD student at UCL, who developed the analysis technique along with colleagues Dr Ingo Waldmann and Marco Rocchetto in UCL Physics & Astronomy. “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.”
Super-Earths are thought to be the most common planetary type in our galaxy and are so-called because they have a mass larger than Earth. The Wide Field Camera 3 (WFC3) on Hubble has already been used to probe the atmosphere of two super-Earths, but no spectral features were found in these previous studies.
55 Cancri e has a year that lasts 18 hours and temperatures on the surface are thought to reach around 2000 degrees Celsius. The planet is located in a solar system around 55 Cancri, a star also known as ‘Copernicus’ in the Cancer constellation that is around 40 light-years from Earth. Because 55 Cancri is such a bright star, the team were able to use new analysis techniques to extract information about its planetary companion.
Observations 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, the researchers 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. 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,” said Professor Giovanna Tinetti of UCL.
Intriguingly, the data also hinted at a signature for hydrogen cyanide, 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 Dr Olivia Venot, KU Leuven, Belgium, who developed an atmospheric chemical model of 55 Cancri e that supported the analysis of the observations.
“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 Professor Jonathan Tennyson, UCL. “Although, hydrogen cyanide or prussic acid is highly poisonous, so it is perhaps not a planet I would like to live on!”
The research at UCL was funded by the Science and Technology Facilities Council (STFC) and the ERC projects ExoLights (617119) and ExoMol. Dr Olivia Venot acknowledges support from the KU Leuven IDO project IDO/10/2013 and from the FWO Postdoctoral Fellowship programme.
The results were summarized by Tsiaras et al. in the paper “Detection of an atmosphere around the super-Earth 55 Cancri e” which was published in the Astrophysical Journal: http://arxiv.org/pdf/1511.08901v2.pdf
The team of astronomers in this study consists of A. Tsiaras (University College London, UK), M. Rocchetto (University College London, UK), I. P. Waldmann (University College London, UK), O. Venot (Katholieke Universiteit Leuven, Belgium), R. Varley (University College London, UK), G. Morello (University College London, UK), G. Tinetti (University College London, UK), E. J. Barton (University College London, UK), S. N. Yurchenko (University College London, UK), J. Tennyson (University College London, UK)
This artist’s impression shows the super-Earth 55 Cancri e in front of its parent star. Using observations made with the NASA/ESA Hubble Space Telescope and new analytic software scientists were able to analyse the composition of its atmosphere. It was the first time this was possible for a super-Earth. 55 Cancri e is about 40 light-years away and orbits a star slightly smaller, cooler and less bright than our Sun. As the planet is so close to its parent star, one year lasts only 18 hours and temperatures on the surface are thought to reach around 2000 degrees Celsius.
Credit: ESA/Hubble, M. Kornmesser
This artist’s impression shows the exoplanet 55 Cancri e as close-up. Due to its proximity to its parent star, the temperatures on the surface of the planet are thought to reach about 2000 degrees Celsius. Scientists were able to analyze the atmosphere of 55 Cancri e. It was the first time this was possible for a super-Earth exoplanet.
Credit: ESA/Hubble, M. Kornmesser
This video shows an artist’s impression of the super-Earth 55 Cancri e moving in front of its parent star. During these transits astronomers were able to gather information about the atmosphere of the exoplanet. The Scientists were able to retrieve the spectrum of 55 Cancri e embedded in the light of its parent star.
The analysis showed that the atmosphere of 55 Cancri e consists mainly of helium and hydrogen with hints of hydrogen cyanide. Credit: ESA/Hubble, M. Kornmesser
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