This is Gliese 486 b, the best-studied terrestrial planet outside the solar system

With data from several ground and space telescopes such as CHARA, CHEOPS, Hubble, MAROON-X, TESS and CARMENES, a team of astronomers led by Joseph A. Caballero from the Centro de Astrobiologia (CAB, mixed center CSIC-INTA) was able to model the interior of the exoplanet Gliese 486 b, estimating the relative sizes of its metallic core and its rocky mantle. Details are published in the magazine Astronomy and Astrophysics.

The team also made predictions about the composition of the atmosphere of this planet, discovered in 2021, as well as its detectability by the James Webb Space Telescope, which will soon point its mirror at the planetary system to which it belongs.

Gliese 486 b has become the Rosetta Stone of exoplanetology. In the solar system we have the terrestrial planets Mercury, Venus, Earth and Mars, and it is now the fifth best studied terrestrial planet in the universe.

José A. Caballero (CAB)

“Gliese 486 b has become the Rosetta stone of exoplanetology”, underlines Caballero, “in the solar system we have the terrestrial planets Mercury, Venus, Earth and Mars; and now the fifth best-studied terrestrial planet in the universe is Gliese 486 b.” However, while it is also one of the closest known transiting planets, traveling at about 10% the speed of light all the time, it would take a probe 260 years to reach it.”

“Probably the most important results behind our work are not the values ​​themselves, but the opportunities they provide for further study,” says the co-author. Ester Gonzalez-Alvarezanother CAB astronomer.

Gliese 486 for future exoplanet science

The researcher refers to future studies, such as the formation of planetary magnetic fields in the outer zone of the core with liquid metals, as Gliese 486 b appears to have one like our Earth. These magnetic fields can act as a shield against storms originating from the stellar host and prevent erosion of the atmosphere.

There are several questions to be answered: could this atmosphere be primitive and made of hydrogen and helium? Or be composed of carbon dioxide and water vapor from volcanic eruptions? Could Gliese 486 b have tectonics?

Although this exoplanet appears to be too hot to be habitable, its precise and accurate characterization could make it the first exoplanet – and only one at the moment – ​​where these kinds of questions can be asked. Just a few years ago, trying to find an answer was considered science fiction.

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The first exoplanet around a star similar to our Sun, 51 Pegasi b, was discovered in 1995. Since then, every year the astronomical community finds less massive, closer and more Earth-like exoplanets.

Various projects and instruments involved

Both Caballero and González-Álvarez collaborate on the CARMENES project, whose consortium is made up of eleven research institutions from Spain and Germany. Its objective is to monitor about 350 red dwarf stars for signs of low-mass planets using a spectrograph installed on the Calar Alto 3.5m telescope in Almería (Spain).

For this study, the team also obtained spectroscopic observations with the MAROON-X instrument, installed on the Gemini North 8.1 m telescope (USA), and with the STIS instrument, aboard Hubble. Photometric observations to derive the planet’s size come from ESA’s ExOPlanets Satellite (CHEOPS) and NASA’s Transiting Exoplanet Survey Satellite (TESS).

The radius of the star was measured with the CHARA array (Center for High Angular Resolution Astronomy) in Mount Wilson, California (USA). A battery of smaller telescopes, including amateur astronomers’ telescopes, were also used to determine the star’s rotation period.

Data from several ground and space telescopes such as CHARA, CHEOPS, Hubble, MAROON-X, TESS and CARMENES were used to carry out the study and predictions about Gliese 486 b

In 2019, the CARMENES consortium discovered the exoplanet that most closely resembles Earth. However, this exoplanet does not transit (that is, it does not pass in front of its star as seen from the solar system) and therefore its radius is difficult to determine precisely.

Although most of them are not habitable, transiting planets – such as Gliese 486 b – are more interesting to the astronomical community because they allow their atmospheres to be investigated and, only for the planetary systems closest to our Sun, their interiors.

The same CARMENES Consortium, in alliance with international teams from the USA, discovered three of the eight closest systems thanks to this type of transiting planets, the last of which was announced last week.


Caballero et al. “A detailed analysis of the planetary system Gl 486”. Astronomy and Astrophysics2022

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