The Longest-period Young Transiting Exoplanets—A Duo of Puffy Giants inside a Debris Disk*

Abstract We identify two large-radius planets around the F-type star HD 114082 as the longest-period young transiting exoplanets known. From the first transit, detected by NASA’s Transiting Exoplanet Survey Satellite (TESS), and a second dip, spotted by the Next-Generation Transit Survey (NGTS), we predicted midtransit times for HD 114082 b (planet b). We pinpoint its orbit (period P b = 225.5504 ± 0.0004 days) from a third transit captured with the ESA’s CHaracterising ExOplanet Satellite and the upgraded Antarctic Search for Transiting ExoPlanets telescope (ASTEP+), alongside orbit-discriminating observations. Another dimming partly covered by ASTEP+ completes the four-transit series. We support with dynamical evidence the planetary nature of a deeper transit detected with TESS and NGTS, identifying planet c. Additionally, we reexamine the debris disk, fitting its excess emission with two dust components. Fundamental stellar parameters are inferred from stellar evolution models, while a joint modeling of photometric and radial velocity time series yields the planetary parameters, with masses further constrained using an N-body code. For planet b, the semimajor axis a b = 0.791 ± 0.008 au, eccentricity e b ≈0, inclination i b = 89 . ° 791 ±0.014, radius R b = 1.046 ± 0.014 R J , and 95% confidence upper limit on its mass M 95%,b = 1.6 M J . For planet c, a c = 0.99 − 0.04 + 0.03 au, e c ≈0, i c = 89 . ° 701 ±0.011, R c = 1.36±0.03 R J , and M 95%,c = 2.0 M J (0.24 M J if adding transit-timing-variation constraints). They seem to be moderate-to-low-mass giants in nearly resonant, coplanar, circular orbits that formed in situ, or beyond the snow line, and migrated inward, shaping the disk.