A hot-Jupiter progenitor on a super-eccentric retrograde orbit.

Giant exoplanets orbiting close to their host stars are unlikely to have formed in their present configurations. These 'hot Jupiter' planets are instead thought to have migrated inward from beyond the ice line and several viable migration channels have been proposed, including eccentricity excitation through angular-momentum exchange with a third body followed by tidally driven orbital circularization. The discovery of the extremely eccentric (e = 0.93) giant exoplanet HD 80606 b (ref. ) provided observational evidence that hot Jupiters may have formed through this high-eccentricity tidal-migration pathway. However, no similar hot-Jupiter progenitors have been found and simulations predict that one factor affecting the efficacy of this mechanism is exoplanet mass, as low-mass planets are more likely to be tidally disrupted during periastron passage. Here we present spectroscopic and photometric observations of TIC 241249530 b, a high-mass, transiting warm Jupiter with an extreme orbital eccentricity of e = 0.94. The orbit of TIC 241249530 b is consistent with a history of eccentricity oscillations and a future tidal circularization trajectory. Our analysis of the mass and eccentricity distributions of the transiting-warm-Jupiter population further reveals a correlation between high mass and high eccentricity.