Ruprecht-Karls-Universität Heidelberg

CARMENES helped in finding exoplanet proxy atmosphere

Artistic impression of the surface of the newly discovered planet Earth Gliese486b. With a surface temperature of about 430 °C a Venus-like hot and dry landscape can be expected. Probably, Gliese has a tenuous atmosphere which due to the planet’s overall parameters is ideally suited for testing methods of analyzing distant planetary atmospheres. (Image: José A. Caballero, Javier Bollaín

By analyzing signals from the star Gliese 486 an international research team discovers a hot rocky super-Earth named Gliese 486b with remains of a planetary atmosphere. This planet is ideally suited to test future observational methods of studying exoplanet atmospheres. Its discovery was made possible by the CARMENES instrument, in whose construction and operation the Landessternwarte Königstuhl (LSW) is decisively involved. The research results were published in the journal "Science".

Meanwhile astronomer have discovered a few thousand exoplanets. Earth-sized planets orbiting in the habitable zone of their host star are of special interest as they offer surface conditions which make the occurrence of extragalactic life most likely. However, for various reasons they are not as easy to find in comparison to more massive planets like Jupiter. CARMENES, the Calar Alto high- Resolution search for M dwarfs with Exoearths with Near-infrared and optical E?chelle Spectrograph, was built to nevertheless enable their detection which now led to the discovery of a new planet ideally suited to test future devices for exoplanet atmospheric analysis.

By applying radial velocity spectroscopy obtained with the CARMENES combined with data from the M-dwarf Advanced Radial velocity Observer Of Neighboring eXoplanets (MAROON-X) spectrograph at the 8.1-m Gemini North telescope located on Hawaii and transit photometry obtained with the Transiting Exoplanet Survey Satellite (TESS), scientists of the CARMENES consortium now found a planet orbiting the red dwarf star Gliese 486 about 26 light-years away from earth that perfectly satisfies the desired model specifications: Gliese 486b, as the new planet was designated, comprises 2.8 times the mass of our home planet and orbits its star at two percent of the distance Earth has to our sun. “The proximity of this exoplanet is exciting because it will be possible to study it in more detail with powerful telescopes such as the upcoming James Webb Space Telescope and the future Extremely Large Telescopes,” explains Trifon Trifonov, planetary scientist at the Max Planck Institute for Astronomy (MPIA) and lead author of the research article.

Gliese 486b orbits its host star in 1.5 days always exposing the same side to the star. This corotational behavior, similar to the one our moon shows while revolving around earth, leads to the planet’s surface heating up to about 430 °C. It probably looks like the hot and dry landscape of Venus but with a tenuous atmosphere constantly dispersed by the intense radiation of the central star.

But what makes Gliese 486b most interesting for astronomers is the whole set of parameters which characterize this exoplanet system, and which play their advantage when the planet for example crosses the surface of the host star from our point of view. Every time this happens, a tiny fraction of the stellar light is absorbed by the thin planetary atmosphere before it reaches Earth. By a method called transit spectroscopy astronomers can separate this tiny imprint off the stellar spectrum and by this means analyze the compound of a planet’s atmosphere. In general, this undertaking is technically extraordinary challenging and will also require space bound instruments like the James Webb telescope, which is going to be launched on October 31, 2021. Calculations by Trivon Trifonov and his colleagues have shown, that in the case of the James Webb telescope the signal to be expected for Gliese 486b will be most pronounced among all prospective candidates known so far.

CARMENES is a novel astronomical measuring instrument designed to detect earth-like planets, particularly planets near low-mass stars like Gliese 486. It is attached to the 3.5-metre telescope of the Calar Alto Observatory near Almería in southern Spain. The highly complex instrument, consisting of two spectrographs, was developed and built by an international consortium of eleven German and Spanish institutions. Researchers from the Landessternwarte Königstuhl (LSW) of the Center for Astronomy of Heidelberg University (ZAH) were significantly involved in its construction and operation. They designed and build one of the two spectrographs and are now in charge of continuously monitoring and improving the quality of the data.

“A nearby transiting rocky exoplanet that is suitable for atmospheric investigation”, T. Trifonov, J. A. Caballero, J. C. Morales et al., Science (2021), DOI:

Dr. Guido Thimm
Zentrum für Astronomie der Universität Heidelberg (ZAH)


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