While it is true that we have discovered hundreds of stars with multiple planets orbiting the galaxy, we have never located a system like this. It orbits the star HD 158259, 88 light years distant from Earth and is truly special.
The six planets present are a “super Earth” and five “mini Neptunes”. Their particularity is that they all share a similar orbital resonance, which means that their orbital periods are related to each other; so much so that they are close to the 3: 2 ratio, as if it were several musicians playing their instruments and that, at a certain moment, they were synchronized to play a melody. This is how this harmonious planetary system is.
New system
The star HD158259 has about the same mass as our Sun, although it is slightly larger. It is almost visible to the naked eye due to its “closeness” (88 light years) in the constellation Draco. It is orbited by these six planets, which, after monitoring them for seven years using the SOPHIE spectrograph installed at the Haute-Provence Observatory in southern France, astronomers discovered that they all did so at a specific rate: they orbit the star in near-perfect orbital resonance. .
“The discovery of this planetary system has been possible thanks to the acquisition of a large number of measurements, as well as a dramatic improvement of the instrument and our signal processing techniques”, explains François Bouchy, professor in the Department of astronomy of the Faculty. of Sciences of the University of Geneva and coordinator of the observation program.
The analysis revealed that these planets have masses two and six times greater than those of the Earth and that it is a compact system, in the sense that the distance from the outermost planet to its star is 2.6 times less than the distance. between Mercury and the Sun.
What is orbital resonance?
It occurs when the orbits of two bodies around their parent body are closely linked, as the two orbiting bodies exert gravitational influence on each other. In our solar system it is a rare phenomenon and probably the best example we have is Pluto and Neptune. These two bodies are in what is described as a 2: 3 orbital resonance. For every two turns Pluto makes around the Sun, Neptune makes three.
How is the orbital harmony of this planetary system?
Each planet in orbit HD 158259 has a resonance of almost 3: 2: that means that for every three orbits each planet makes, the next one completes two. And for every three orbits of the second, the third makes two, and so on. Mind you, the planets in HD158259 are close to, but not exactly within, resonance , suggesting that these worlds were trapped in resonance at the time of their formation, but then exited without completely losing orbital relationship. each.
Orbital resonance, which we have observed in other multiplanetary systems such as TRAPPIST-1 or Kepler-80, may be key to keeping certain systems stable. In these systems, planets form far from the star and then move closer and closer due to their interaction with the disk of material from which they formed. When it comes to multiple planets, these migrations can end up knocking a planet into a star or another planet, or kicking it out of the system. But if the planets lock into a resonance, their migration may remain stable.
Referencia: NC Hara, et al. The SOPHIE search for northern extrasolar planets XVI. HD 158259: A compact planetary system in a near-3:2 mean motion resonance chain. Astronomy & Astrophysics 2020. https://doi.org/10.1051/0004-6361/201937254
