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Gliese 486 b, a prime target for the James Webb Telescope

Gliese 486 b could help astronomers better understand the atmospheres of rocky planets. This world will soon be targeted by the James Webb Telescope, which is still scheduled for launch in October.

Gliese 486 b is an exoplanet recently discovered by researchers at the Max Planck Institute for Astronomy in Heidelberg (Germany) thanks to the CARMENES spectrograph, available at the Calar observatory Alto (Spain). This instrument searches for planets via the "radial velocity" method, noting slight oscillations in a star's motion caused by the gravitational tug of an orbiting world.

The team then relied on NASA's TESS satellite. The latter also probes the presence of nearby exoplanets, but by relying on another method:that of transit. Concretely, he will notice the tiny drops in luminosity of a star. However, these are most often caused by the passage of a planet between this star and our point of view.

A 'Rosetta Stone' for atmospheric surveys

These two approaches have made it possible to draw a first "portrait" of this planet. Gliese 486 b orbits a red dwarf star only 26 light-years away . It is approximately 1.3 times larger and 2.8 times more massive than the Earth. It completes one revolution of its star in 1.47 Earth days .

Knowing the size and mass of the planet, the researchers were also able to estimate its density:about 7 g per cubic centimeter. For comparison, the density of the Earth is 5.5 g per cubic centimeter. In other words, as reported by the journal Science, Gliese 486 b therefore probably has an iron silicate composition similar to that of our planet.

Finally, its surface temperature is estimated at around 430°C . According to the researchers, it's probablycold enough to support an atmosphere and warm enough that this atmosphere can be studied from afar .

This combination "of physical and orbital characteristics of Gliese 486 b thus makes it the "Rosetta Stone" for atmospheric investigations of rocky exoplanets “, says Trifon Trifonov, lead author of the study. As a reminder, the Rosetta stone is a fragment of an engraved stele from ancient Egypt bearing three versions of the same text which allowed the decipherment of hieroglyphics in 1799.

A target for the JWT

The best candidate to make such observations is none other than the James Webb Telescope, which has just completed its final functional tests and is scheduled to launch in the fall. "Shortly after the JWST is operational, we will be able to plan sightings of Gliese 486 b “, notes the astronomer. “Being optimistic, we could know whether or not the planet has an atmosphere and, if so, what its composition is within three years “.

Note that given its surface temperature, Gliese 486 b is not an excellent candidate for the search for life . Trifon Trifonov imagines a world "hot and dry, interspersed with volcanoes and glowing rivers of lava “.

Also, because its orbit is so tight, the planet is likely "locked", still showing the same face to its star, like the Moon with Earth. Thus, the exoplanet could well have an extremely hot day side and a much colder night side. Again, this is another possible obstacle to life as we know it.