Researchers manage to classify hundreds of planetary systems into just 4 categories
Most of the known exoplanets belong to systems of several planets. The way they are "arranged" with respect to their star varies greatly from system to system. A team of researchers has however managed to reduce the types of planetary systems to only 4.
The order of planets in our solar system is atypical compared to other planetary systems in the galaxy.
While more than 5,300 planets have been discovered in the galaxy since 1995, one thing is clear: our solar system is not the rule. The classification which consists in positioning the telluric planets close to the star, and the gas giants in the distance, is only one provision among others. Thus, some gas giants have been observed stuck to their star. Other systems are made up of Earth-like planets, or super-Earths of identical sizes that seem to be mass-produced.
Nothing to do with ours, which contains the tiny Mercury and the gigantic Jupiter. Faced with so much diversity, it was tempting to imagine that there is an infinity of possible planetary systems. But no, says a team of scientists from the Universities of Bern and Geneva (Switzerland). Sifting through observations including the Kepler space telescope, the researchers classified the planetary systems according to only four categories: "similar", "ordered", "anti-ordered" and "mixed".
Our solar system is "ordered"
Planetary systems in which the masses of the planets are almost identical to each other fall into the "similar" category. When the mass of planets tends to increase with distance from the star, they are "ordered". This is the case with ours. If, on the contrary, the mass of the planets decreases with the distance from the star, it is an "anti-ordered" architecture.
Finally, the "mixed" type corresponds to a system in which the masses vary a lot from one planet to another. " Now, for the first time, we have a tool that allows us to study planetary systems as a single entity and compare them to other systems ," said Lokesh Mishra in a statement from the University of Geneva. , lead author of the study. Our results show that "like" planetary system architecture is most common. About eight out of ten systems around stars visible in the night sky have such an architecture."
Understand the origin of different types of planetary systems
The "ordered" category, like ours, seems to be the rarest. The next step will be to determine the factors that explain the formation of one planetary system rather than another, knowing that planets form within rings of gas and dust. This gets complicated because the answer to this question depends on the training models considered, and there are several of them. But starting from their own, the "Bern model", the authors estimate that " the '"similar"" systems emerge from relatively small and not very massive disks. On the contrary, massive disks containing many heavy elements mainly give rise to "ordered" and "anti-ordered" systems. Finally, "mixed" systems However, these hypotheses will have to be confirmed by other models.
Artist's impression of the 4 categories of planetary systems. Credits: NCCR PlanetS, Tobias Stierli
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