CHEOPS telescope discovers key new planetary system

An artist's rendering of the CHEOPS space telescope orbiting Earth. Esa/atg

An international team including scientists from the Universities of Geneva and Bern has identified a key new planetary system using the CHEOPS space telescope.

According to an article published on Wednesday in the “Nature” scientific journal, the discovery could help researchers in their study of the atmospheric composition of exoplanets.

The system is characterised by the fact that its six planets orbit the central star in perfect harmony. The planet closest to the star completes six full revolutions in 55 days, while the planet furthest away completes a single rotation in exactly the same time. The other planets also orbit according to the same precise chain of resonance.

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“We know of around 5,000 exoplanets, but systems in which the resonances extend over such a long chain of six planets are extremely rare”, said Hugh Osborn, astrophysicist at the University of Bern and co-author of the study.

Exoplanets are planets which orbit stars other than the sun in our solar system.

This characteristic enables scientists to know that the system has remained largely unchanged since its formation over a billion years ago, according to Osborn. Young planetary systems tend to move in resonance, but most lose this rhythm over time. Meteorite impacts, for example, can upset the fragile balance.

Potential for science

Such systems are of particular importance to science, because studying them enables us to draw conclusions about the formation of exoplanets. “And if we know more about other planets, we will ultimately know more about the Earth” and its peculiarities, explains the scientist.

The star HD110067 at the centre of the system holds great potential for research, not least because it is particularly bright. This makes it an ideal candidate for study, because the brighter a star is, the more visible it is to telescopes, explains Osborn.

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When the planets pass in front of the star at the centre of the system, the light filters through the planetary atmospheres, adds Jo Ann Egger, a doctoral student at the University of Bern and co-author of the study, quoted in a press release. In this way, astronomers can determine the chemical composition and other properties of the atmospheres. For this to be possible, the star must be particularly bright, as is the case for HD110067.

The planets in the system do not, however, resemble the Earth, Osborn stressed. These mini-Neptunes are two to three times larger than the Earth, have a very low density and a hydrogen-rich atmosphere, according to the researchers.

The planets orbiting HD110067 were spotted for the first time in 2020 by a NASA satellite called Tess (Transiting Exoplanet Survey Satellite), enabling the orbits of two of them to be calculated. But it was the CHEOPS (CHaracterising ExOPlanets Satellite) space telescope that solved the enigma of the complete system, said Osborn.

CHEOPS discovered another planetary system with a resonance chain in 2021, orbiting the star TOI-178. However, the particular luminosity of the HD110067 system and its six planets evolving in harmony make it a much more interesting object of study than TOI-178, concluded Osborn.

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