One of the closest exoplanets to us in the constellation of Cancer, first discovered in 2004, has recently become the focus of space telescopes Hubble, Spitzer and the largest ground-based observatories. Thanks to new astronomical instruments and data analysis algorithms, it has now been possible to determine the presence and composition of its atmosphere. For exoplanets of the "super-earth" class, such work has been done for the first time.
The binary star 55 Cancer has long attracted attention. It is visible in the sky with the naked eye, since it is only 40.9 light years away from us and has a luminosity of 0.6 solar. The main star in this system belongs to the same main spectral type (GxV) as the Sun. Its mass is also close to that of the Sun, and at least five planets revolve around it. Each of them was detected by Doppler spectroscopy. Then the discovery of exoplanets was confirmed with the help of observations carried out at the orbiting and largest ground-based observatories.
Among all exoplanets discovered in a sun-like star, the greatest attention of astronomers is now attracted by 55 Cancer e. It is a super-earth with a high carbon content. With a mass of 8.37 earths and a radius of 2.17 times that of the earth, conditions must be created in its bowels for the intensive formation of diamonds. According to primary estimates, their total volume exceeds the size of the Earth. Additional interest in the exoplanet was due to the fact that mathematical models predicted the presence of a dense atmosphere with a high probability of water vapor content.
The Hubble Space Telescope (Image: nasa.gov).
For a long time, they tried to confirm or deny these data, specifying the parameters of the planet, its possible composition and origin. Since 2014, the most advanced instrument on the Hubble Space Telescope, the WFC3 camera, has been used for this. However, observations in visible and near infrared light made it possible to determine only regular transits of an exoplanet against the background of the parent star, without providing new information.
The researchers were helped by the successful location of exoplanet 55 Cancer e. Since it is 64 times closer to its star than the Earth is to the Sun, it lasts only 18 hours a year, and the surface heats up to 2000 K. Due to strong heating, it glows in the mid-infrared range. Infrared luminosity, which is rare for planets, makes it possible to study it not only by means of observations in the optical range, but also by the apparatus of the Spitzer orbiting telescope.
The Spitzer Space Telescope (Image: NASA / JPL-Caltech).
The combined data collected by the Hubble and Spitzer space telescopes and ground-based observatories have allowed researchers at University College London to judge the composition of the exoplanet's gas envelope. Methods of spectral analysis of chemical composition are widely used to study the stars and the atmosphere of the planets of the solar system, but for a distant super-earth, they turned out to be equally informative for the first time.
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Large amounts of hydrogen and helium were found in the atmosphere of exoplanet 55 Cancer. She probably captured these light elements early on from a cloud of ionized gas during the formation of the local sun. Despite all expectations and preliminary calculations, water vapor in the exoplanet's atmosphere has not yet been detected even in trace quantities.
Due to the intense heating by the star 55 Cancer A, the super-Earth's crust constantly melts during the day and barely has time to cool down overnight. With ascending heat fluxes, particles of carbon and its compounds, mostly inorganic, constantly enter the atmosphere. In the course of various reactions, oxides, hydrogen cyanide (hydrogen cyanide vapor) and acetylene are mainly formed. The predominance of carbon monoxide over carbon dioxide indicates a high carbon to oxygen ratio. “The presence of hydrogen cyanide and other molecules we have discovered may be confirmed in a few years by next generations of infrared telescopes. In this case, we will receive new evidence that this planet is extremely rich in carbon and in general, very unusual,”- commented one of the study's authors, Jonathan Tennyson (Jonathan Tennyson).
Andrey Vasilkov