It is difficult for us to “solve” the history of the formation and migration of planetary systems, because sooner or later, many of them, for one reason or another, lose their “balance” and deviate from their rhythmic orbits. Sometimes their planets even collide with each other. Therefore, systems that maintain their rhythm are very valuable. One of them is Trappist-1. Finally, scientists explained the unusual rhythm of the orbital rotation of the seven planets.

The Trappist-1 system is located 40 light-years away. At its center is a small and cold red dwarf, about 10 times smaller than the Sun. Seven planets fly around it: four are comparable in mass to Earth, the rest are half as much. Despite their size, they are not habitable. The system is so compact that it can easily fit into the orbit of Mercury. Its main feature is the resonant motion of the planets.

Orbital resonance is a situation where the periods of planetary oppositions are associated with natural numbers. In the Trappist-1 system, the planets resonate in pairs: 8:5, 5:3, 3:2, 3:2, 4:3 and 3:2. Thus, for every eight revolutions of the first Trappist-1b planet, the second Trappist-1c planet manages to make five revolutions. Meanwhile, they rotate rapidly. The first one orbits the star in 1.5 Earth days, while the most distant one, Trappist-1h, orbits in 18.7 Earth days.

Such rhythmicity is a sign that the system’s planets have “preserved” their simple migration history in the disk, i.e. under the influence of gravitational forces between the forming planets and the gas in the protoplanetary disk. The problem is that such migration in a system like Trappist-1 would have produced simpler resonances between the planets closest to the star. As computer modeling shows, Trappist-1b, c and d would have a 3:2 rhythm rather than an 8:5 and 5:3 rhythm.

Scientists have attempted to explain the resonance change between the Trappist-1 planets due to special conditions in the disk. They suggest that the Trappist-1 disk is 50 times more effective in influencing the planets than would be expected from such a system.

In a new study, the results of which were published in the journal Nature AstronomyAstronomers have proposed a different scenario. They started with the idea of ​​dispersing and eliminating the boundaries of the protoplanetary disk. In this case, it turns out that the planets themselves change their rotation rhythm.

According to the calculations of the authors of the new study, the inner planets of the Trappist-1 system, namely Trappist-1b, c, d and e, formed 3:2 resonances when the disk near the star began to disperse. Then the planets closest to the star began to “fall” into the gap that opened up. Meanwhile, the planet farthest from the star, Trappist-1e, was “pulled” into the inner boundary of the protoplanetary disk.

The disk continued to disintegrate. TRAPPIST-1e “followed” it, moving away from the inner planets and losing the “rhythmic” connection with them. At the same time, the inner planets continued to approach the star, reaching the most mysterious resonances of 8:5 and 5:3.

At some point, the planet Trappist-1e “collided” with a pair of outer planets, Trappist-1f and g, as it followed the disk and migrated “inward”. They “knocked” it out of the disk boundary and Trappist-1e began its orbit towards the star, where it met up with Trappist-1d again. During the convergence process, Trappist-1e probably went through 9:5, 5:3, 8:5 resonances with Trappist-1d and returned to a 3:2 rhythm. Then, planet h migrated outward and resonated with planet g. This is how the modern Trappist-1 system was born.

“By studying Trappist-1, we were able to test new hypotheses about the evolution of planetary systems. Trappist-1 is very interesting because of its complexity and long planetary chain. It is a great sample to test alternative theories about the formation of planetary systems,” explained Gabrielle Picchierri (Gabriele Pichierri)A researcher from the California Institute of Technology (USA) and one of the authors of the new study. He works in the group of Professor Kostyantyn Batygin, one of the creators of the hypothesis of the existence of the ninth planet of the Solar System. He co-authored a new publication.