190 light years from Earth, the TOI-1130 star system intrigues the scientific community. It houses a Hot Jupitera typically solitary gas giant, and a mini-Neptune orbiting even closer to the star.
Discovered in 2020 thanks to the TESS satellite, this system defied models of planetary formation, because the gravity of a hot Jupiter would be expected to eject any companion so close.
How can we explain such cohabitation?
The key to the mystery lies in the atmosphere of the smaller planet, TOI-1130b. Thanks to observations from the James Webb telescope, an international team led by MIT was able to analyze the composition of its atmosphere.
Published in the Astrophysical Journal Letters, the results reveal a heavy atmosphererich in water vapor, carbon dioxide and sulfur dioxide. Such a composition is impossible if the planet had formed so close to its star, where only light elements like hydrogen and helium would dominate.
This discovery suggests that mini-Neptune and its massive companion trained much furtherin the cold region of the protoplanetary disk, beyond the frost line.
Saugata Barat, researcher at MIT and lead author of the study, emphasizes: ” This is the first time we have observed the atmosphere of a planet located inside the orbit of a hot Jupiter. “
What is the story of their migration?
The preferred hypothesis is that of a joint migration. Both planets would have formed in the icy reaches of the system, accumulating atmospheres rich in ice and other volatile compounds. Over time, they would have been gradually attracted towards their star.
This tandem journey allowed them to remain linked by an orbital resonance (the mini-Neptune completes two orbits for each orbit of the hot Jupiter), thus preserving their unique configuration.
Chelsea X. Huang, who discovered the system, calls it one of a kind. Normally, hot Jupiters are ” so massive, and their gravity so strong, that anything within their orbit is simply ejected “. The survival of TOI-1130b is evidence of the process of gradual migration.
Something new for the mini-Neptunes
This analysis confirms the existence of a new formation channel for mini-Neptunes, the most common type of planet in our galaxy. Until now, their presence so close to a star remained a puzzle. The study of the TOI-1130 system shows that they can form in cold areas and migrate inwards, retaining their dense atmosphere.
