Astronomers have identified more than 5,300 planets in our Milky Way. Some are part of a real planetary system. Like our solar system… Or not quite, we learn from Swiss researchers today.
Since HD 114,762 b, the very first exoplanet discovered in the late 1980s, astronomers have identified more than 5,300 planets orbiting stars other than our Sun, spread across more than 850 planetary systems with at least three exoplanets – or two confirmed planets and others candidates . Two of them show up with eight confirmed planets and one, Trappist-1, with seven exoplanets. The star closest to our sun, Proxima CentauriProxima Centauri, has given birth to at least three planets.
The planets of the Trappist 1 system formed quickly and suffered few impacts
Astronomers thought there were only two ways to arrange these exoplanets around their star. But today, Swiss researchers show for the first time that all these planetary systems can be divided into four different architectures.
So there are the systems that they call “similar”. Those where neighboring planets are almost identical. Planetary systems in which the mass of the planets tends to increase with distance from the star fall into the “ordered” category. This is the case with our solar system. The “anti-ordinate” category corresponds to systems in which the mass of the planets decreases with distance from the star. Finally, scientists speak of a “mixed” system to describe a planetary system in which the masses of the planets vary significantly and differently from one planet to another.
An architecture that reflects the initial cloud
The astronomers note that this nomenclature can also be applied to other quantities, such as radius, density or water content on exoplanets. What is finally possible to be able to compare the planetary systems with each other on the basis of a simple tool.
From this work it is already clear that the “similar” planetary system architecture is the most widespread. It affects about eight out of ten systems. While the “ordered” architecture – that of our solar system – appears to be the rarest. Differences that would be due to the configuration of the gas and dust cloud from which the exoplanets in question formed. A relatively small and not very massive disk would be the origin of “similar” systems. In contrast, massive disks containing many heavy elements would produce mainly “ordered” and “anti-ordered” systems. Finally, the “mixed” systems would be the result of medium-sized hard drives. Without forgetting that the dynamic interactions between the planets, such as collisions or ejections, also affect the final architecture.
“One of the remarkable aspects of these results is that they link the initial conditions of star and planet formation to a property that can be observed today: the architecture of the planetary system. In between lie billions of years of evolution. For the first time, we have succeeded in establishing a connection despite such a large time interval in order to be able to make verifiable predictions. It will be exciting to see if these predictions hold up over time,” concludes Yann Alibert, Professor of Planetary Sciences at the University of Bern, in a press release.