TOI-1130b
TOI-1130b is a warm mini-neptune exoplanet (3.66 R⊕, 19.8 M⊕, equilibrium temperature ~825 K) and the inner planet of the toi-1130 multi-planet system. It is locked in a 2:1 mean motion resonance with an outer hot Jupiter — a rare and dynamically informative architecture.
JWST atmospheric characterization (Barat et al., 2026)
A combined jwst NIRSpec G395H + NIRISS SOSS transmission spectrum reports (src-jwst-toi-1130b-atmosphere-2026-05):
- H₂O at 7.5σ
- CO₂ at 3.3σ
- SO₂ at 3.6σ
- CH₄ tentative at ~2σ
- No significant He I 1.083 μm absorption; mass-loss rate <10¹¹ g/s
- Atmospheric metallicity logZ/Z⊙ = 1.8 (+0.4/−0.3)
- C/O ratio <0.75 at 3σ
- Mean molecular weight μ = 5.5 (+1.3/−0.8) amu — a high-mean-molecular-weight-atmosphere, not hydrogen-dominated
- Strong optical slope in NIRISS/SOSS consistent with TESS and CHEOPS transit-depth measurements
Formation interpretation
The volatile-rich, high-μ atmosphere plus the outer hot Jupiter’s “pebble-filtering” of inner-disk solids supports ex-situ formation beyond the water-ice-line followed by inward planetary-migration — coherent with the present 2:1 resonance. This volatile-rich pathway also helps explain TOI-1130b’s position at the edge of the planetary “radius cliff,” and argues that the mini-neptune population is not a homogeneous formation class.
Significance
TOI-1130b expands the JWST sub-Neptune sample beyond the contested k2-18b / hycean case, offering a cleaner volatile-rich interior interpretation without the biosignature controversy. It is a methodological reference for how JWST transmission-spectroscopy constrains atmospheric mean molecular weight and metallicity on warm mini-Neptunes.