Cheops space telescope discovered mysterious planetary constellation

Researchers have discovered an unusual planetary system with the Cheops space telescope. The six planets orbit the star TOI-178, which is more than 200 light-years away, in a harmonic rhythm, according to the Universities of Bern and Geneva.

Artist impression of the TOI-178 planetary system (ESA)

The cameras of NASA's Transiting Exoplanet Survey Satellite (Tess) already pointed to three planets orbiting the star TOI-178. This planetary system has now also been targeted by an international research team with the participation of astrophysicists from Bern and Geneva. With the help of the Espresso spectrograph of the European Southern Observatory in Chile, they discovered two more planets in the system.

The celestial bodies identified so far orbit the star in the constellation Sculptor harmoniously: Their orbital periods are two, three, six, ten and 20 days. That is, the ratio of the numbers results in simple fractions.

Sixth planet found

"Our theory implied that there could be an additional planet in this harmony; however, its orbital period would have to be very close to 15 days," Bernese astrophysicist Adrien Leleu was quoted as saying in the release. And indeed, Cheops found an additional, sixth planet orbiting the star in 15 days, the researchers report in the journal Astronomy and Astrophysics.

The observation of this last, mysterious planet almost threatened to fall through. Early last October, a piece of debris from a Chinese satellite the size of a milk carton threatened to come dangerously close to Cheops. So researchers had to take evasive action. To the relief of the exoplanet researchers, this was accomplished in time for observations to resume.

Very different densities

According to the calculations, the planets have a 1.1 to three times Earth's radius and have very different densities. For example, in the TOI-178 system, a dense, terrestrial planet like Earth appears to be right next to a very fluffy planet with half the density of Neptune. This is followed by one very similar to Neptune. It is the first time such a wild density mix has been observed in a planetary system, said Kate Isaak, a project scientist with the European Space Agency (ESA).
Cheops is a joint ESA-Swiss mission led by the University of Bern in collaboration with the University of Geneva. Unlike previous missions, the space telescope, which flies at an altitude of 700 kilometers, is not designed to detect new exoplanets, but actually takes a closer look at ones that are already known.