DETECTION OF AN ATMOSPHERE AROUND THE SUPER-EARTH 55 CANCRI E

By Angelos Tsiaras, Marco Rocchetto, Ingo P. Waldmann, O. Venot, Ryan Varley, G. Morello, M. Damiano, Giovanna Tinetti, E. J. Barton, Sergei N. Yurchenko and 2 more. 2015

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We report the analysis of two new spectroscopic observations in the near-infrared of the super-Earth 55 Cancri e, obtained with the WFC3 camera on board the Hubble Space Telescope. 55 Cancri e orbits so close to its parent star that temperatures much higher than 2000 K are expected on its surface. Given the brightness of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length and a very high scanning speed. We use our specialized pipeline to take into account systematics introduced by these observational parameters when coupled with the geometrical distortions of the instrument. We measure the transit depth per wavelength channel with an average relative uncertainty of 22 ppm per visit and find modulations that depart from a straight line model with a 6σ confidence level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably hydrogen-rich. Our fully Bayesian spectral retrieval code,  ?> -REx, has identified HCN to be the most likely molecular candidate able to explain the features at 1.42 and 1.54 μm. While additional spectroscopic observations in a broader wavelength range in the infrared will be needed to confirm the HCN detection, we discuss here the implications of such a result. Our chemical model, developed with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic than previously thought.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

A Population Study of Gaseous Exoplanets (2017, methodology): “…Morello et al. 2015) and super-Earths (e.g. Bean et al. 2010; Berta et al. 2012; Knutson et al. 2014b; Kreidberg et al. 2014b; Demory et al. 2016; Tsiaras et al. 2016b) allow us to learn important properties of the planets analysed, we can only gain a limited insight into the global population…”
A NEW APPROACH TO ANALYZING HST SPATIAL SCANS: THE TRANSMISSION SPECTRUM OF HD 209458 b (2015, methodology): “At the top, the case of HD 209458 b, studied in this work, and at the bottom, the case of 55 Cancri e (Tsiaras et al. 2016), a much longer scan.”
HD 209458b in new light: evidence of nitrogen chemistry, patchy clouds and sub-solar water (2017, background): “In another effort, Tsiaras et al. (2016b) also detected H2O but were unable to robustly constrain its abundance.”
Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects (2019, background): “Neptunes and super-Earths, are becoming feasible, giving rise to the fledgling area of exogeology (265, 74, 277).”
THE IMPRINT OF EXOPLANET FORMATION HISTORY ON OBSERVABLE PRESENT-DAY SPECTRA OF HOT JUPITERS (2016, background): “Tentative evidence for planets with carbon-rich atmospheres exists for types of planets other than hot Jupiters like HR8799b (Lee et al. 2013) or 55 Canc e (Tsiaras et al. 2016).”