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First results from CHEOPS reveal an exoplanet with extreme conditions

The CHEOPS space telescope is living up to its promise: its first observations reveal the face of the exoplanet WASP-189b - a planet where extreme conditions prevail. CHEOPS is a European Space Agency (ESA) mission led by Swiss laboratories, with the participation of numerous French laboratories including IPGP-Université de Paris.

First results from CHEOPS reveal an exoplanet with extreme conditions

Publication date: 29/09/2020

Press, Research

Related themes : Origins

Eight months after CHEOPS went into orbit around the Earth, the first scientific publication using data from this new space telescope has just been published. CHEOPS is the first European mission to explore exoplanets* that have already been identified. It was designed as part of a collaboration between ESA, Switzerland and a dozen European countries, including France**. A consortium of more than a hundred scientists and engineers was involved in building the satellite over a five-year period. The LAM, the only French laboratory involved in the mission design, played a key role in the mission’s success. Its planetology team designed and produced the software that automatically processes the CHEOPS data.

Artist's view of the CHEOPS space telescope orbiting the Earth (© ESA / ATG medialab)

One of the most extreme planets known

The object of the observations made by CHEOPS for this first result is WASP-189b, an exoplanet orbiting the star HD 133112. Larger and hotter than our Sun, it emits a bluish light. It is located 322 light years from Earth, in the constellation of Libra.

Monika Lendl, astrophysicist at the University of Geneva, who coordinated the study, describes the exoplanet as follows: “WASP-189b is twenty times closer to its star than the Earth is to the Sun; it circles the Sun in less than three days! What’s more, it is a giant planet measuring one and a half times the size of Jupiter, which is the largest planet in our solar system. Also, because of its proximity to its star, it has an extreme temperature, which is why it is called an ultra-hot Jupiter.”

Planetary objects such as WASP-189b are out of the ordinary. Due to the very intense tidal effects resulting from their proximity to their star, they have a day side permanently exposed to the star’s light and a night side, always in shadow. This is what distinguishes its climate from that of the gas giants such as Jupiter and Saturn in our solar system. Based on the CHEOPS observations, the scientific team estimates the temperature of WASP-189b at 3,200 degrees Celsius. Such temperatures are capable of vaporising iron, making WASP-189b one of the most extreme planets known to date.

Surreal artist's image of CHEOPS in front of the day side of the planet WASP-189b, with the star at its back illuminating it in blue (© Frederik Peeters / David Ehrenreich)

Extremely precise measurements of luminosity

As it is currently impossible to obtain an image of a planet so distant from the Earth and so close to its star, CHEOPS measures the light from the stars with great precision, observing a tiny decrease in the star’s luminosity each time the exoplanet passes between CHEOPS and HD 133112. This passage, known as a ‘transit’, is an indirect sign of the presence of an exoplanet.

Surprisingly, when it is the planet’s turn to pass behind the star, an even fainter decrease in light is also observed. In fact, the fact that the exoplanet WASP-189b is very close to its star makes its daylight side so bright that researchers can measure the amount of “missing” light when the planet passes behind HD 133112. By observing several passes of WASP-189b behind its star, they were able to deduce its luminosity. The team found that the planet reflects very little light from its star, due to the absence of clouds, which are unable to form at such high temperatures. As a result, the planet heats up strongly and also emits light: it glows red.

Sébastien Charnoz, a professor in the Cosmochemistry, Astrophysics and Experimental Geophysics team at the Institut de Physique du Globe de Paris, explains: “At such temperatures, even rocks are vaporised. For astrophysicists, this is an extremely exotic environment to study. The diversity of planetary environments is extraordinarily rich.”

The star itself is unique

The CHEOPS measurements are so precise that they allow us to learn more about WASP-189b’s host star. In fact, the decrease in light recorded by CHEOPS during the transits is not constant, suggesting that the star’s surface has zones that are darker than others. Scientists believe that these variations occur when HD 133112 rotates very quickly, causing the star to become slightly deformed and elongated. The parts furthest from its centre then become colder and therefore darker.

Key parameters of the WASP-189 system (© ESA)

These initial results from CHEOPS are remarkable and extremely promising. This highly luminous system, with its extreme conditions, will serve as a benchmark for future studies. ” The next publications are already being prepared”, reveals Willy Benz, Professor of Astrophysics at the University of Bern and scientific leader of CHEOPS.

* Exoplanets are planets orbiting stars other than the Sun. The detection of the first exoplanet in 1995, from the Haute Provence Observatory, was rewarded with the 2019 Nobel Prize in Physics awarded to the Swiss scientists Michel Mayor and Didier Queloz.

** France is fully involved in CHEOPS: the Marseille Astrophysics Laboratory (LAM-Aix-Marseille University, CNRS, CNES) developed the data processing and calibration software. The Institut de Physique du Globe de Paris (IPGP-Université de Paris), the LAM, the IPAG (Université Grenoble-Alpes), the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE-Observatoire de Paris, Université PSL, Sorbonne Université) and the Institut d’Astrophysique de Paris (IAP, CNRS, Sorbonne Université) are involved in the scientific analysis of data on subjects as diverse as the dynamics of planetary systems and the analysis of their stability, the measurement of the intensity of tidal effects and the deformation of celestial bodies, the precise determination of the radius of planets, and the possible detection of rings, satellites or co-orbits.

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