تركيبة غير متوقعة لغلاف تابع لكوكب نبتون الصغير الدافئ سريع

الملخص الأصلي

كما كتبه المؤلفون، بالإنجليزية arXiv:2605.02036

We present the combined JWST/NIRSpec G395H and NIRISS SOSS transmission spectrum of a warm mini-Neptune, TOI-1130b (3.66 R$$_{\oplus}$$, 19.8 M$$_{\oplus}$$, $$T_{eq}\sim825$$ K). It is part of a rare and unique multi-planet system TOI-1130, which hosts an inner mini-Neptune and an outer hot Jupiter locked in a 2:1 mean motion resonance. From the transmission spectrum of TOI-1130b we detect multiple molecules -- H$$_2$$O (7.5$$\sigma$$), CO$$_2$$ (3.3$$\sigma$$), and SO$$_2$$ (3.6$$\sigma$$), as well as a tentative detection of CH$$_4$$ ($$\sim$$2$$\sigma$$). We find a strong optical slope in the NIRISS/SOSS spectrum, which is consistent with TESS and CHEOPS transit depth measurements. From equilibrium chemistry retrievals we measure the atmospheric metallicity ($$\log{Z/Z_{\odot}}=1.8^{+0.4}_{-0.3}$$) and C/O ratio ($$<$$0.75 at 3$$\sigma$$ level confidence) and constrain the atmospheric mean molecular weight, $$\mu$$ = 5.5$$^{+1.3}_{-0.8}$$ amu. These constraints are consistent with self-consistent forward model grids. We detect no significant He I 1.083$$\mu$$m absorption signal and put a mass-loss rate upper limit of $$10^{11}$$g\s$$^{-1}$$. The volatile-rich high mean molecular weight atmosphere of TOI-1130b along with the `pebble-filtering' effect of the outer hot Jupiter supports the ex-situ formation scenario beyond the water ice line and subsequent migration, coherent with its present orbital architecture. A volatile-rich formation scenario could also potentially explain the location of TOI-1130b at the edge of the `radius cliff'. This result hints that the mini-Neptune population may not a homogeneous formation history; rather, volatile-rich ex-situ formation also contributes to its population.