TESS Spots a Hot Jupiter with an Inner Transiting Neptune

Abstract

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 ) with a 4.1 days period, and a hot Jupiter ( ) with an 8.4 days period. Precise radial-velocity observations show that the mass of the hot Jupiter is . For the inner Neptune, the data provide only an upper limit on the mass of 0.17  (3 σ ). 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.