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

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Gliese 486b 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 to launch in October.

Gliese 486 b is an exoplanet recently discovered by researchers at the Max Planck Institute for Astronomy in Heidelberg (Germany) using the CARMENES spectrograph, available at the Calar Alto observatory (Spain). This instrument searches for planets using the “radial velocity” method, noticing slight oscillations in the motion of a star caused by the gravitational pull of an orbiting world.

The team then relied on NASA’s TESS satellite. The latter also probes the presence of nearby exoplanets, but 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 made it possible to draw a first “portrait” of this planet. Gliese 486b evolves around a red dwarf star at only 26 light years. She is around 1.3 times larger and 2.8 times more massive than Earth. She completes a tour of her star in 1.47 earth day.

By 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 the review relates Science, Gliese 486 therefore probably has an iron silicate composition similar to that of our planet.

Finally, its surface temperature is estimated at about 430 ° C. According to the researchers, it is probably cold enough to endure an atmosphere and warm enough for 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 surveys on 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 decryption of hieroglyphics in 1799.

A target for the JWT

The best candidate for making 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 JWST is operational, we will be able to plan sightings of Gliese 486 b“, Notes the astronomer. “By being optimistic, we could know if the planet has an atmosphere or not and, if so, what is its composition within three years.“.

Gliese 486b revolves around a red dwarf star about 30% as massive as the Sun. Credit: RenderArea

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

Also, because its orbit is so tight, the planet is probably “locked”, always 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.





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