Mapping Directly Imaged Giant Exoplanets

TL;DR

This paper explores how time-resolved photometric and spectroscopic observations can be used to analyze the atmospheres and surface heterogeneity of directly imaged giant exoplanets, revealing properties like rotation, cloud cover, and atmospheric composition.

Contribution

It introduces techniques for interpreting light curves and spectra to determine exoplanet surface features, rotation periods, and atmospheric heterogeneity, advancing the understanding of exoplanet atmospheres.

Findings

Simulations differentiate between homogeneous and patchy atmospheres.

Future instruments can recover rotation periods and cloud properties.

Principal component analysis can map planetary surfaces from light curves.

Abstract

With the increasing number of directly imaged giant exoplanets the current atmosphere models are often not capable of fully explaining the spectra and luminosity of the sources. A particularly challenging component of the atmosphere models is the formation and properties of condensate cloud layers, which fundamentally impact the energetics, opacity, and evolution of the planets. Here we present a suite of techniques that can be used to estimate the level of rotational modulations these planets may show. We propose that the time--resolved observations of such periodic photometric and spectroscopic variations of extrasolar planets due to their rotation can be used as a powerful tool to probe the heterogeneity of their optical surfaces. We address and discuss the following questions: a) what planet properties can be deduced from the light curve and/or spectra, and in particular can we determine rotation periods, spot--coverage, spot colors, spot spectra; b) what is the optimal configuration of instrument/wavelength/temporal sampling required for these measurements; and, c) can principal component analysis be used to invert the light curve and deduce the surface map of the planet. Our simulations describe the expected spectral differences between homogeneous (clear or cloudy) and patchy atmospheres, outline the significance of the dominant absorption features of water, methane, and CO and provide a method to distinguish these two types of atmospheres. Simulated photometry from current and future instruments is used to estimate the level of detectable photometric variations. We conclude that future instruments will be able to recover not only the rotation periods, cloud cover, cloud colors and spectra but even cloud evolution. We also show that a longitudinal map of the planet's atmosphere can be deduced from its disk--integrated light curves.