TESS Spots a Hot Jupiter with an Inner Transiting Neptune

2020 
Hot Jupiters are rarely accompanied by other planets within a factor of a few in orbital distance. Previously, only two such systems have been found. Here, we report the discovery of a third system using data from the Transiting Exoplanet Survey Satellite (TESS). The host star, TOI-1130, is an eleventh magnitude K-dwarf in Gaia G-band. It has two transiting planets: a Neptune-sized planet (3.65 ± 0.10 R⊕) with a 4.1 days period, and a hot Jupiter (1.50^(+0.27)_(-0.22 R_J) with an 8.4 days period. Precise radial-velocity observations show that the mass of the hot Jupiter is 0.974^(+0.043)_(-0.044 M_J. For the inner Neptune, the data provide only an upper limit on the mass of 0.17 M_J (3σ). Nevertheless, we are confident that the inner planet is real, based on follow-up ground-based photometry and adaptive-optics imaging that rule out other plausible sources of the TESS transit signal. The unusual planetary architecture of and the brightness of the host star make TOI-1130 a good test case for planet formation theories, and an attractive target for future spectroscopic observations.
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