Giant Outer Transiting Exoplanet Mass (GOT ‘EM) Survey. VI. Confirmation of a Long-period Giant Planet Discovered with a Single TESS Transit

Abstract

We report the discovery and confirmation of TOI-4465 b, a 1.25 R _J ${}_{-0.07{R}_{{\rm{J}}}}^{+0.08{R}_{{\rm{J}}}}$ , 5.89 M _J ± 0.26 M _J giant planet orbiting a G dwarf star at d ≃ 122 pc. The planet was detected as a single-transit event in data from Sector 40 of the Transiting Exoplanet Survey Satellite (TESS) mission. Radial velocity (RV) observations of TOI-4465 showed a planetary signal with an orbital period of ∼102 days and an orbital eccentricity of e = 0.24 ± 0.01. TESS reobserved TOI-4465 in Sector 53 and Sector 80 but did not detect another transit of TOI-4465 b, as the planet was not expected to transit during these observations based on the RV period. A global ground-based photometry campaign was initiated to observe another transit of TOI-4465 b after the RV period determination. The ∼12 hr long transit event was captured from multiple sites around the world and included observations from 24 citizen scientists, confirming the orbital period as ∼102 days. TOI-4465 b is a relatively dense (3.73 ± 0.53 g cm ^−3 ), temperate (375–478 K) giant planet. Based on giant planet structure models, TOI-4465 b appears to be enriched in heavy elements at a level consistent with late-stage accretion of icy planetesimals. Additionally, we explore TOI-4465 b’s potential for atmospheric characterization and obliquity measurement. Increasing the number of long-period planets by confirming single-transit events is crucial for understanding the frequency and demographics of planet populations in the outer regions of planetary systems.

Keywords

• Exoplanets
• Radial velocity
• Transit photometry
• Planetary system formation