Paris (AFP)

The young exoplanet observation space telescope, Cheops, has revealed the face of one of the most extreme known, with a surface temperature of 3,200 degrees Celsius, according to a recent study.

It is only five feet tall, but from its observation post, orbiting the Earth since last December, CHEOPS sees far.

In this case, the exoplanet WASP-189b, which revolves around the star HD 133112, far from our solar system, 322 light years away, in the constellation Libra.

Everything is out of the ordinary in this couple who belong to the tribe of more than 4,000 exoplanets listed to date, celestial bodies orbiting around a star other than the sun, identified since the first in 1995.

WASP-189b is an ultra-hot, Jupiter-like gas giant.

She is twenty times closer to her star than we are to ours.

With the consequence of making the tour in less than three days, against a year for the blue planet.

The proximity to its sun is not without consequence on its temperature.

Because its host star is "very large, much more massive and hotter than our sun", around 7,700 degrees, told AFP Monika Lendl, of the Geneva Observatory, which coordinated the study, published on 23 September in Astronomy & Astrophysics.

"We would like to understand how it is possible for planets to exist so close to their star and what happens to them in extreme circumstances," adds the scientist.

- Very close to the host star -

Launched last December, CHEOPS is tasked with a first characterization of exoplanets.

"He must study already known systems, for which we know that there is a transit", that is to say a passage of the planet in front of its star, explains Jacques Laskar, director of the Institute of Celestial Mechanics and Computation. ephemeris (IMCCE), at the Paris Observatory.

The result of a partnership between the European Space Agency (ESA) and Switzerland, benefiting from the cooperation of a hundred engineers and scientists from eleven European states, the telescope is equipped with a photometric device that precisely measures the radiation luminous emitted by a star, and where appropriate that reflected by its exoplanet.

“We cannot see WASP-189b per se, because it is very close to its host star, which is very bright,” Lendl explains.

A bit like a rabbit dazzled by headlights who cannot see a car.

But CHEOPS can measure the differences in light emitted between when the exoplanet passes in front of, then next to, and finally behind its star.

We can deduce the distance that separates it, and the time it takes to go around it.

“This allows us to accurately calculate the size of the planet, but also the amount of light it reflects,” explains Mde Lendl.

These measurements also made it possible to determine that the host star deforms under the effect of a very rapid rotation.

- Harvest expected -

With the help of other instruments, such as SOPHIE, the spectrograph of the Observatory of Grasse, whose telescope allowed the discovery of the first exoplanet, we can measure its mass.

"All this allows us to say whether a planet is rocky or gaseous, and to classify it", explains Prof. Laskar.

The WASP-189b study is just the first in an expected harvest with the ongoing review of around 30 other systems, including some multi-planetary, that CHEOPS has been examining since its launch.

Its scientists are not looking for a habitable place.

For that, it will be necessary to wait for the help of other instruments, which will make it possible to classify more precisely the systems explored by CHEOPS.

Like the James Webb Space Telescope, Hubble's successor to be launched in 2021, which will be able to study the molecular composition of the atmosphere of a candidate for further exploration.

Next, ESA's Plato mission will study terrestrial planets orbiting a sun in a habitable zone.

With a launch planned after 2025.

Without forgetting Gaia, the satellite mapping the stars of our galaxy since 2014, whose third data delivery, expected in early December, will enrich the catalog of exoplanets close to our solar system.

© 2020 AFP