Obliquity of an Earth-like planet from frequency modulation of its direct imaged lightcurve: mock analysis from general circulation model simulation

TL;DR

This study demonstrates that analyzing frequency modulation in direct-imaged lightcurves of Earth-like exoplanets can effectively estimate their obliquity within a few degrees, aiding future characterization efforts.

Contribution

It introduces a novel method using frequency modulation of lightcurves from GCM simulations to determine planetary obliquity, enhancing exoplanet characterization techniques.

Findings

Obliquity can be estimated within a few degrees accuracy.

Frequency modulation analysis is effective for Earth-twin exoplanets.

Method is feasible with a 4 m space telescope at 10 pc.

Abstract

Direct-imaging techniques of exoplanets have made significant progress recently, and will eventually enable to monitor photometric and spectroscopic signals of earth-like habitable planets in the future. The presence of clouds, however, would remain as one of the most uncertain components in deciphering such direct-imaged signals of planets. We attempt to examine how the planetary obliquity produce different cloud patterns by performing a series of GCM (General Circulation Model) simulation runs using a set of parameters relevant for our Earth. Then we use the simulated photometric lightcurves to compute their frequency modulation due to the planetary spin-orbit coupling over an entire orbital period, and attempt to see to what extent one can estimate the obliquity of an Earth-twin. We find that it is possible to estimate the obliquity of an Earth-twin within the uncertainty of several degrees with a dedicated 4 m space telescope at 10 pc away from the system if the stellar flux is completely blocked. While our conclusion is based on several idealized assumptions, a frequency modulation of a directly-imaged earth-like planet offers a unique methodology to determine its obliquity.