Detecting Planetary Oblateness in the Era of JWST: A Case Study of Kepler-167e

TL;DR

This paper introduces an efficient algorithm to detect planetary oblateness using JWST transit data, demonstrating that single transits of Kepler-167e can reveal Saturn-like oblateness or set upper limits, aiding understanding of planetary formation.

Contribution

The authors develop a new computational method for analyzing transit light curves to detect planetary oblateness and apply it to JWST observations of Kepler-167e, highlighting its potential for characterizing cold exoplanets.

Findings

JWST can detect Saturn-like oblateness in Kepler-167e with a single transit.

A slight spin-orbit misalignment enhances oblateness detectability.

The method sets upper limits on oblateness for planets with aligned spins.

Abstract

Planets may be rotationally flattened, and their oblateness thus provide useful information on their formation and evolution. Here we develop a new algorithm that can compute the transit light curve due to an oblate planet very efficiently and use it to study the detectability of planet oblateness (and spin obliquity) with the James Webb Space Telescope (JWST). Using the Jupiter analog, Kepler-167e, as an example, we show that observations of a single transit with JWST are able to detect a Saturn-like oblateness ($f=0.1$) with high confidence, or set a stringent upper limit on the oblateness parameter, as long as the planetary spin is slightly misaligned ($\gtrsim 20^\circ$) with respect to its orbital direction. Based on known obliquity measurements and theoretical arguments, it is reasonable to believe that this level of misalignment may be common. We estimate the sensitivity limit of JWST in oblateness detections and highlight the importance of better characterizations of cold planets in planning future JWST transit observations. The potential to detect rings, moons, and atmospheric species of the cold giants with JWST is also discussed.