Astronomers have discovered a six-planet system that orbits the star HD 158259, which is 88 light-years away. The planet system is composed of a super-Earth and five mini Neptunes that display an exceptionally regular spacing. Astronomers said that the almost perfect orbital resonance of the planet system hints at how it may have formed.
The star, HD 158259, is about the same mass but a little larger than the Solar System's Sun. Astronomers found the six-planet system in the Draco constellation using the SOPHIE spectrograph installed at the Haute-Provence Observatory in the South of France, the Deccan Herald reported.
They published their finding in the journal Astronomy & Astrophysics.
The Six-Planet System With Almost Perfect Orbital Resonance
Astronomer Nathan Hara of the University of Geneva in Switzerland led an international team of researchers who used the SOPHIE spectrograph and the TESS exoplanet-hunting space telescope to study the six-planet system.
Astronomers have been monitoring the six-planet system orbiting HD 158259 for seven years when they found that the planets were in almost perfect orbital resonance. According to ADS, orbital resonance happens when two or more systems or planets orbiting their parent body exert gravitational influence on each other.
In the Solar System, the best example of orbital resonance is Pluto and Neptune, although experts noted that orbital resonance is rare in planetary systems.
The six-planet system has been closely linked to the distance of the outermost planet to its star, which is 2.6 smaller than the distance between Mercury and the Sun, the researchers said.
Moreover, they said that each planet orbiting HD 158259 is almost in 3:2 orbital resonance with the next planet out away from their star. This was also described as a period ratio of 1.5, which means that when a planet completes three orbits, the next one also completes two orbits.
The astronomers said that the planets were orbiting closely with orbits that are 2.17, 3.4, 5.2, 7.9, 12, and 17.4 days, or period ratios of 1.57, 1.51, 1.53, 1.51, and 1.44 between each pair of planets, according to ScienceAlert. this might not be a perfect resonance, but it is close enough for the six-planet system orbiting HD 158259 to be classified as an extraordinary planet system.
The closest planet to the star is the super-Earth, which TESS revealed to be twice the Earth's size.
The Planets Did Not Form in the Planet System
The astronomers believe that the almost perfect orbital resonance of the planet system is a sign that the planets did not form there. Astronomer Stephane Udry of the University of Geneva said that there were compact systems with several planets that are believed to form far from the star before migrating towards it.
They said that the resonances play an important role in forming compact systems wherein the planetary embryos in the protoplanetary disc grow and migrate towards the star away from the disc's outer edge. This produces a chain of orbital resonance throughout the planetary system.
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