Two decades after the discovery of 51 Peg b , the formation processes and atmospheres of short-period gas giants remain poorly understood . Observations of eccentric systems provide key insights on those topics as they can illuminate how a planet ’ s atmosphere responds to changes in incident flux . We report here the analysis of multi-day multi-channel photometry of the eccentric ( e \sim 0.93 ) hot Jupiter HD 80606 b obtained with the Spitzer Space Telescope . The planet ’ s extreme eccentricity combined with the long coverage and exquisite precision of new periastron-passage observations allow us to break the degeneracy between the radiative and dynamical timescales of HD 80606 b ’ s atmosphere and constrain its global thermal response . Our analysis reveals that the atmospheric layers probed heat rapidly ( \sim 4 -hr radiative timescale ) from < 500 K to 1400K as they absorb \sim 20 \% of the incoming stellar flux during the periastron passage , while the planet ’ s rotation period is 93 ^ { +85 } _ { -35 } hours , which exceeds the predicted pseudo-synchronous period ( 40 hours ) .