Models of Warm Jupiter Atmospheres: Observable Signatures of Obliquity

TL;DR

This study models the atmospheric circulation of hypothetical warm Jupiters with varying obliquities to identify observable signatures, demonstrating that upcoming telescopes like JWST can measure or constrain their obliquities through eclipse mapping.

Contribution

It introduces three-dimensional atmospheric models for warm Jupiters across a range of obliquities and predicts observable signatures for upcoming telescope observations.

Findings

JWST can constrain obliquities of warm Jupiters to within 10 degrees.

Eclipse mapping can directly measure obliquity if it is greater than or equal to 30 degrees.

Observable thermal phase curves depend strongly on viewing geometry and obliquity.

Abstract

We present three-dimensional atmospheric circulation models of a hypothetical "warm Jupiter" planet, for a range of possible obliquities from 0-90 degrees. We model a Jupiter-mass planet on a 10-day orbit around a Sun-like star, since this hypothetical planet sits at the boundary between planets for which we expect that tidal forces should have aligned their rotation axes with their orbital axes (i.e., ones with zero obliquity) and planets whose timescale for tidal alignment is longer than the typical age of an exoplanet system. In line with observational progress, which is pushing atmospheric characterization to planets on longer orbital periods, we calculate the observable signatures of obliquity for a transiting warm Jupiter: in orbital phase curves of thermal emission and in the hemispheric flux gradients that could be measured by eclipse mapping. For both of these predicted measurements, the signal that we would see depends strongly on our viewing geometry relative to the orientation of the planet's rotation axis, and we thoroughly identify the degeneracies that result. We compare these signals to the predicted sensitivities of current and future instruments and determine that the James Webb Space Telescope should be able to constrain the obliquities of nearby warm Jupiters to be small (if less than or equal to 10 degrees) or to directly measure them if significantly non-zero (greater than or equal to 30 degrees), using the technique of eclipse mapping. For a bright target and assuming photon-limited precision, this could be done with a single secondary eclipse observation.