Located approximately 190 light-years from Earth, a unique planetary duo orbits the star TOI-1130. This system features a hot Jupiter, a massive planet closely circling its star, alongside a smaller gas-rich planet known as a mini-Neptune, which orbits even closer.
This pairing is unusual, as hot Jupiters typically exist in isolation due to their powerful gravitational forces, which tend to eliminate nearby planets. Nonetheless, the mini-Neptune has persisted in this environment, raising intriguing questions for astronomers since its identification in 2020.
Recent observations from NASA's James Webb Space Telescope have shed light on this anomaly. Researchers propose that both planets likely originated beyond the star's "frost line," a region in the protoplanetary disk where temperatures are low enough for water to freeze into solid ice, allowing for the accumulation of material necessary for planet formation. These findings were published in the Astrophysical Journal Letters.
"Hot Jupiters are typically solitary, with their gravitational pull scattering potential companions," explained Chelsea X. Huang, who initially discovered this system. "However, the survival of the mini-Neptune alongside this hot Jupiter prompts us to reconsider how such systems can form."
Exploring the Atmosphere of TOI-1130b
The research team utilized the Webb telescope to analyze the atmosphere of the mini-Neptune, TOI-1130b. The planets are in a mean motion resonance, which complicates the timing of their transits. This required the team to model years of previous observations to predict when the mini-Neptune would transit in front of its star.
During this event, starlight filtered through the planet's atmosphere, allowing the Webb telescope to measure the wavelengths absorbed. This absorption pattern reveals the chemical composition of the atmosphere, providing vital clues about the planet's formation.
Results indicated the presence of heavier molecules like water vapor, carbon dioxide, sulfur dioxide, and traces of methane. The unexpected abundance of these heavier compounds suggests that TOI-1130b formed in a colder region of the system, rather than close to its star.
A New Perspective on Planetary Migration
The evidence points to both planets forming beyond the frost line, where icy materials can accumulate. As TOI-1130b migrated closer to its star, the ice would have vaporized, leaving behind the chemical signatures observed.
This gradual inward migration likely explains the mini-Neptune's survival alongside the hot Jupiter. A rapid gravitational disturbance could have destabilized the system, while a slow drift allowed both planets to maintain stable orbits.
"This marks the first observation of an atmosphere from a planet within a hot Jupiter's orbit," stated Saugata Barat, lead author of the study. "The findings confirm that mini-Neptunes can form in colder regions and migrate inward over time."
Such discoveries challenge existing assumptions about planetary formation, suggesting that many mini-Neptunes may have originated in the cold depths of protoplanetary disks before gradually moving inward. This system exemplifies the diverse architectures that can exist in our galaxy.