Detecting the Wind-Driven Shapes of Extrasolar Giant Planets from Transit Photometry

TL;DR

This paper develops a theoretical framework to understand how winds and other processes can distort the shape of extrasolar giant planets, affecting transit lightcurves and measurements.

Contribution

It introduces a model linking planetary dynamics to shape deviations and assesses their impact on transit observations.

Findings

Planet shapes are unlikely to cause detectable lightcurve deviations.

Shape distortions can introduce systematic errors in measuring planetary parameters.

Theoretical predictions are based on a model of HD189733b.

Abstract

Several processes can cause the shape of an extrasolar giant planet's shadow, as viewed in transit, to depart from circular. In addition to rotational effects, cloud formation, non-homogenous haze production and movement, and dynamical effects (winds) could also be important. When such a planet transits its host star as seen from Earth, the asphericity will introduce a deviation in the transit lightcurve relative to the transit of a perfectly spherical (or perfectly oblate) planet. We develop a theoretical framework to interpret planet shapes. We then generate predictions for transiting planet shapes based on a published theoretical dynamical model of HD189733b. Using these shape models we show that planet shapes are unlikely to introduce detectable lightcurve deviations (those >~1e-5 of the host star), but that the shapes may lead to astrophysical sources of systematic error when measuring planetary oblateness, transit time, and impact parameter.