Astronomers have identified a rare star system in which all the planets are in resonance. This means that the system has remained virtually unchanged since its inception. Located in the northern constellation Veronica’s Hair, about 100 light-years from Earth, is the star HD110067 of spectral class K0. In 2020, the TESS space telescope detected rhythmic decreases in the brightness of the radiation; This is a clear sign of the existence of exoplanets. After preliminary analysis of the data, scientists hypothesized that there must be two objects.

A few years later, in 2022, TESS astronomers repeated the observation of the star. Although, according to new, more complete data, it once again turned out that two planets were flying next to HD110067, scientists did not manage to explain all the features of the observations.

A few more transits were found in the new data that did not match previous exoplanet candidates. Then Raphael Luke became interested in the unusual system (Rafael Luque) from the University of Chicago and colleagues. The group decided to use the Cheops space telescope. This small device was created and launched specifically to study already discovered exoplanets with bright stars in nearby systems. With his help, scientists found a third planet in the system, which became the key to the discovery of the others.

Three planets (HD110067b, HD110067c and HD110067d) were found to be in 3:2 and 3:2 orbital resonances. If they are in a resonance chain, the other planets of the system, if any, must follow this rhythm. Otherwise the balance would have been upset long ago.

Using this assumption, the team was able to match orbital resonances to explain all of HD110067’s remaining dips in the TESS observation data. Thus, the researchers obtained six exoplanets with resonances in pairs of 3:2, 3:2, 3:2, 4:3 and 4:3.

The system’s first planet, with an orbital period of about nine Earth days, rotates three times, while the second rotates twice, and so on. One revolution of the farthest exoplanet, whose orbital period is about 54 Earth days, corresponds to six revolutions of the nearest exoplanet. The results of the research were published at: Nature.

When the system is newly formed, the planets are mostly in resonance, but the balance is easily disrupted. The reason may be a very powerful planet, a strong collision of objects within the system, or an approach to another star. According to the article’s author, Raphael Luque, scientists believe that only 1% of all systems maintain orbital resonance. This is why the “pure configuration” of the HD110067 system is so interesting to researchers.

Only two “resonance” systems consisting of six planets are known: HD158259 and TOI-178, systems with super-Earths and mini-Neptunes. By the way, during the “decoding” researchers also used the Cheops telescope. Based on the data collected, scientists were able to determine the mass of three planets in the system and make an estimate of the mass of the remaining three. Therefore, the mass of the “lightest” planet, HD110067e, would have to be less than 3.9 Earth masses. And the “heaviest” turned out to be HD110067d, which has a mass of 8.5 times the mass of the Earth. For comparison: Neptune is approximately 17 times larger than the Earth by this indicator.

Exoplanets, which are between Earth and Neptune in mass, are found in more than half of the sun-like stars. Many scientists believe that, at best, the conditions on these cosmic bodies are very suitable for life. Equilibrium temperature of HD110067 planets: from 440 Kelvin at the farthest to 800 Kelvin at the closest to the star.

But we don’t fully understand how they form and evolve, and the composition of both the planet and its atmosphere depends on this. Judging by the mass and density of the three exoplanets of the HD110067 system, they are surrounded by thick hydrogen atmospheres.