The study focuses on TOI‑1130b, a mini‑Neptune orbiting a star about 190 light‑years from Earth. The planet completes an orbit in just a few days and is exposed to extreme temperatures. Despite this, observations made with the James Webb Space Telescope reveal an atmosphere rich in water vapour, as well as other heavy molecules such as carbon dioxide and Sulphur dioxide. This composition is difficult to reconcile with formation in the planet’s current, star‑proximate orbit.
A rare and dynamically rich system
The TOI‑1130 system stands out because it hosts two very different planets in relatively close orbits: an inner mini‑Neptune and an outer Jupiter‑sized planet. Such configurations are rare, as massive planets like hot Jupiters often dominate the dynamics of a system and eject or scatter smaller neighbours.
“TOI‑1130 is a rare puzzle because hot Jupiters are usually lonely, with gravity strong enough to scatter away any close‑in neighbours. Here, a mini‑Neptune survives in the inner system, in a special orbital configuration that keeps the two planets gravitationally coupled",says Judith Korth.
Constraining migration through dynamics
A central challenge in the study was to understand how the mini‑Neptune could have formed far from its star and later migrated inward without losing its atmosphere or destabilising the system. This is where dynamical analysis and transit timing variations become crucial.
Korth contributed to the analysis of transit data, the subtle, periodic dimming of starlight as planets pass in front of their host star. In systems like TOI‑1130, where two planets orbit relatively close to each other, these transits do not occur with perfect regularity. Instead, the planets exert small but measurable gravitational tugs on each other, altering the timing of their orbits.
“The mini‑Neptune and hot Jupiter are caught close to a mean‑motion resonance, with orbital periods near a 2:1 ratio,” Korth explains.
“Their mutual gravitational tugs lock them into a coordinated dance rather than driving them apart. This kind of resonant coupling is a hallmark of planets that drifted inward together through a protoplanetary disk.”
According to Korth, smooth and gradual migration is one of the few mechanisms capable of capturing two planets into resonance and keeping them there over time without triggering instability or scattering.
“The fact that the TOI‑1130 planets remain close to this configuration, together with the heavy, volatile‑rich atmosphere now detected on the inner mini‑Neptune, points to a gentle inward journey from beyond the frost line as the only origin story that keeps both worlds intact,” she says.
Linking atmosphere and dynamics
By combining the James Webb Space Telescope's precise atmospheric measurements with detailed dynamical modelling, the researchers were able to connect the planet’s present‑day atmosphere to its formation and migration history. Contributions such as Korth’s are essential for linking observed atmospheric properties to physical pathways of planet formation.
Overall, the study improves our understanding of how common exoplanets like mini‑Neptunes form and evolve and highlights the importance of dynamical studies for interpreting the growing volume of high‑precision data from new space‑based observatories such as JWST.
Judith Korth carried out this work during her time at Lund University and is currently affiliated with the university. She is now a Postdoctoral Researcher at the Instituto de Astrofísica de Canarias.
Read the full research article in The Astrophysical Journal Letters.
Judith Korth's profile in the Lund University Research Portal.