Warm Jupiters Beyond the Tidal Synchronization Limit may Exhibit a Wide Range of Secondary Eclipse Depths

Abstract

With the JWST we can now characterize the atmospheres of longer-orbit planets, but this moves us into a regime where we cannot assume that tidal forces from the star have eroded the planets’ obliquities and synchronized their rotation rates. These rotation vectors may be tracers of formation and evolution histories and also enable a range of atmospheric circulation states. Here we delineate the orbital space over which tidal synchronization and alignment assumptions may no longer apply and present three-dimensional atmospheric models of a hypothetical warm Jupiter over a range of rotation rates and obliquities. We simulate the secondary eclipses of this planet for different possible viewing orientations and times during its orbital, seasonal cycle. We find that the eclipse depth can be strongly influenced by the rotation rate and obliquity through the timing of the eclipse relative to the planet’s seasonal cycle, and advise caution in attempting to derive properties such as albedo or day–night transport from this measurement. We predict that if warm Jupiters beyond the tidal limit have intrinsic diversity in their rotation vectors, then this will manifest itself as dispersion in their secondary eclipse depths. We explore eclipse mapping as a way to uniquely constrain the rotation vector of warm Jupiters but find that the associated signals are likely at the edge of the JWST performance. Nevertheless, as the JWST begins to measure the secondary eclipses of longer-orbital-period planets, we should expect to observe the consequences of a wider range of rotation states and circulation patterns.

Keywords

• Exoplanet atmospheres
• Atmospheric dynamics
• Exoplanets
• Extrasolar gaseous planets
• James Webb Space Telescope
• Eclipses