New Delhi: Astronomers have analysed the atmospheres of a pair of unusual planets in orbit around the star designated as TOI-1130 at a distance of 306
lightyears from the Earth, revealing the origins of the formation of the unusual system. The pair of planets were discovered in 2020, and do not fit into conventional models of planet formation, where ice and gas giants form in the outer reaches of the star system. Hot Jupiters also tend to scatter any inner star system worlds because of their gravitational influence. Observations by Webb have revealed that the smaller planet holds a heavy atmosphere incompatible with formation in its present location.
The atmosphere of the Sub-Neptune is rich in water vapour, carbon dioxide and sulphur dioxide with hints of methane. A planet with such an atmospheric composition could not have formed so close to the host star, where lighter envelopes of hydrogen and helium are expected. Both planets likely accreted their atmospheres beyond the frost line in the star system, where water condenses to ice, allowing the accumulation of volatiles onto rocky cores. The two planets formed in the outer portions of the star system then migrated inwards gradually.
Rare formation trajectory
This system demonstrates that Sub-Neptunes can form far beyond the frost line of the host star and migrate inwards in lockstep with a Hot Jupiter, while retaining its thick atmosphere. The observations counter assumptions that Sub-Neptunes close to the host stars must possess light envelopes. The research establishes that such a migration pathway exists in nature. Sub-Neptunes are the most common exoplanet type in the Milky Way, but rarely appear in such configurations. The star system has a unique architecture, that is valuable for refining models of planet formation and evolution. The research also highlights the diversity of processes shaping planetary systems across the galaxy. A paper describing the research has been published in Astrophysical Journal Letters.
