A peculiar pair of planets is orbiting a star roughly 190 light years away in the Milky Way galaxy. This strange duo, a hot Jupiter and a mini-Neptune, has puzzled astronomers since it was discovered in 2020. Now, researchers from MIT have examined the mini-Neptune’s atmosphere, revealing insights into the origins of this unusual planetary system.
Published in Astrophysical Journal Letters, the study uses data from NASA’s James Webb Space Telescope (JWST) to analyze the mini-Neptune’s atmosphere. This marks the first time scientists have assessed the atmospheric composition of a mini-Neptune that orbits inside a hot Jupiter. The findings show a dense atmosphere rich in water vapor, carbon dioxide, sulfur dioxide, and traces of methane, suggesting the planet did not form near its current position.
Instead, the research suggests that both the mini-Neptune and the hot Jupiter originated much farther from the star, in a cooler area of the system’s early protoplanetary disk. This region would allow the planets to build icy and volatile-rich atmospheres. Over time, gravitational forces may have drawn them closer to the star while retaining their atmospheres.
The study provides the first evidence that mini-Neptunes can form beyond a star’s frost line, where temperatures are low enough for water to freeze. “This is the first time we’ve observed the atmosphere of a planet that is inside the orbit of a hot Jupiter,” said Saugata Barat, the lead author and postdoc at MIT’s Kavli Institute for Astrophysics and Space Research. He confirmed that the mini-Neptune formed beyond the frost line.
The research team, including Andrew Vanderburg from MIT and collaborators from various institutions like the Harvard and Smithsonian Center for Astrophysics, used NASA’s Transiting Exoplanet Survey Satellite (TESS) to initially identify the system. They observed the star TOI-1130, finding signs of both a mini-Neptune and a hot Jupiter orbiting the star every four and eight days, respectively.
Chelsea X. Huang, who discovered the system while at MIT, noted that hot Jupiters typically have no companions due to their massive gravity scattering nearby objects. Yet, this system defies that norm, raising questions about its formation.
The 2020 discovery prompted further investigation by Huang, Vanderburg, and others using JWST. The team analyzed TOI-1130b, the mini-Neptune, overcoming challenges like predicting its orbital path, which was influenced by its interaction with the hot Jupiter.
Judith Korth from Lund University led efforts to predict when JWST could best observe the planets. Successfully capturing detailed observations, the team utilized JWST’s ability to detect various wavelengths to determine the atmospheric composition of the planets.
The results indicated the presence of heavier molecules in TOI-1130b’s atmosphere, contradicting earlier assumptions that mini-Neptunes forming close to their stars would have lighter atmospheres. The planet likely gathered its heavy atmosphere beyond the frost line, where water and other volatiles condensed into icy particles.
Barat stated that the detection of heavy molecules in TOI-1130b’s atmosphere supports the theory that it and its hot Jupiter companion formed at the system’s edge. Gradual migration allowed them to remain close and retain their atmospheres. “This system represents one of the rarest architectures that astronomers have ever found,” Barat explained. “The observations of TOI-1130b provide the first hint that such mini-Neptunes that form beyond the water/ice line are indeed present in nature.”
Original Source: news.mit.edu
