The Impact of Circumplantary Jets on Transit Spectra and Timing Offsets for Hot-Jupiters

TL;DR

This paper models how circumplanetary jets affect the transit spectra and timing of hot Jupiters, predicting observable signatures that can inform about atmospheric dynamics and are detectable with current or future telescopes.

Contribution

It introduces detailed 3D hydrodynamical models linking circumplanetary jet strength to observable transit signatures, including spectral and timing variations.

Findings

Transit depth decreases with stronger jets.

Timing offsets up to 6 seconds at high-opacity wavelengths.

Ingress-egress spectral differences increase with jet strength.

Abstract

We present theoretical wavelength-dependent transit light curves for the giant planet HD209458b based on a number of state of the art 3D radiative hydrodynamical models. By varying the kinematic viscosity in the model we calculate observable signatures associated with the emergence of a super-rotating circumplanetary jet that strengthens with decreased viscosity. We obtain excellent agreement between our mid-transit transit spectra and existing data from Hubble and Spitzer, finding the best fit for intermediate values of viscosity. We further exploit dynamically driven differences between eastern and western hemispheres to extract the spectral signal imparted by a circumplanetary jet. We predict that: (i) the transit depth should decrease as the jet becomes stronger; (ii) the measured transit times should show timing offsets of up to 6 seconds at wavelengths with higher opacity, which increases with jet strength; (iii) wavelength-dependent differences between ingress and egress spectra increase with jet strength; (iv) the color-dependent transit shape should vary more strongly with wavelength for stronger jets. These techniques and trends should be valid for other hot Jupiters as well. Observations of transit timing offsets may be accessible with current instrumentation, though the other predictions may require the capabilities JWST and other future missions. Hydrodynamical models utilized solve the 3D Navier-Stokes equations together with decoupled thermal and radiative energy equations and wavelength dependent stellar heating.