Astronomers have discovered that not all gas giant planets form in the same way and that their formation depends on the stars they orbit.
In a paper, published in Astronomy & Astrophysics, the team provides evidence that planets less than four times the mass of Jupiter form mostly around stars rich in heavy elements, while bigger gas giants orbit stars that are more metal-poor and more massive.
This apparent division fits perfectly with formation models. According to the theory, it’s possible to form gas giant planets in two ways: Gas giants might form through core accretion, when the planet-size chunk of ice or rock (the "core") draws in enough gas to form a thick envelope around itself, or it can form due to gravitational instabilities in the gas disk itself, forming like a star – although a lot smaller.
Researchers weren’t sure if both of these mechanisms happened in the universe and, if so, whether they led to different objects. But thanks to the new study, it appears that the different types of gas giants form in only one of two ways.
“The result now published suggests that both mechanisms may be at play, the first forming the lower mass planets, and the other one responsible for the formation of the higher mass ones,” lead author Nuno Cardoso Santos said in a statement.
This research implies that Jupiter, which weighs 320 times the Earth, and the other Solar System giants are actually part of a population smaller in mass that formed from core accretion.
The discovery was based on statistical analysis of publically available data collected by Kepler and many other observatories in the last several years.
Co-author Vardan Adibekyan added: “Our team, using public exoplanet data, obtained an interesting observational evidence that giant planets such us Jupiter and its larger mass cousins, several thousand times more massive than the Earth (of which we do not have an example in the Solar System) form in different environments, and make two distinct populations."
There is a lot we don’t understand about planet formation. In a recent press conference, for example, NASA researchers said they discovered that small planets come in two groups as well. Missions like Gaia and the future James Webb Space Telescope will help us detect more worlds and uncover more about how our own Solar System came to be.