Direct Measure of Radiative and Dynamical Properties of an Exoplanet Atmosphere

TL;DR

This study uses precise multi-channel photometry from the Spitzer Space Telescope to analyze the atmospheric response of the eccentric hot Jupiter HD 80606 b, revealing rapid heating and a longer-than-expected rotation period.

Contribution

It provides the first direct measurement of the radiative and dynamical timescales of an exoplanet's atmosphere during periastron passage, improving understanding of atmospheric behavior in eccentric gas giants.

Findings

Atmosphere heats rapidly with a ~4 hr radiative timescale.

The planet's rotation period is 93 hours, longer than predicted.

The atmosphere absorbs about 20% of stellar flux during periastron.

Abstract

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~ 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 (~4 hr radiative timescale) from $\lt$500 to 1400 K as they absorb ~ 20% of the incoming stellar flux during the periastron passage, while the planet's rotation period is 93$\pm_{35}^{85}$ hr, which exceeds the predicted pseudo-synchronous period (40 hr).