Characterizing the Dynamics and Chemistry of Transiting Exoplanets with the Habitable World Observatory

TL;DR

This paper discusses the capabilities of the Habitable Worlds Observatory to characterize transiting exoplanets' atmospheres through spectroscopic phase curves, extending studies to cooler planets and incorporating UV and polarimetry data.

Contribution

It introduces the HWO's potential for detailed atmospheric characterization of cooler exoplanets using broad wavelength coverage and polarimetry, expanding beyond current telescope capabilities.

Findings

HWO can observe planets with orbital periods of 5-20+ days.

UV and NIR coverage enables comprehensive atmospheric analysis.

Polarimetry aids in aerosol classification and understanding atmospheric energy balance.

Abstract

The primary scientific objective of this Habitable Worlds Observatory (HWO) Science Case Development Document (SCDD) is to measure planetary rotation rates of transiting exoplanets to determine the structure, composition, circulation, and aerosol properties of their planetary atmospheres. For this analysis, HWO would obtain spectroscopic phase curves for planets with orbital periods of 5 - 20+ days, to assess tidal locking radius assumptions. Extending phase curve studies out to longer orbital periods than accessible with current and near-future telescopes will enable detailed investigation of atmospheric structure, composition, and circulation for planets that are much cooler than the more highly irradiated planets accessible with JWST phase curve observations (i.e., Teq < 500 K for HWO versus 1400 K <= Teq <= 2600 K for JWST). Broad wavelength coverage extending from the UV to the NIR would capture both reflected light and thermal emission, enabling HWO to conduct comprehensive characterization of planetary atmospheres. UV observations would probe high altitudes, thereby providing valuable insights into atmospheric (dis)equilibrium, aerosol properties, and the effects of photochemical processes on atmospheric composition. We also discuss the role of polarimetry in the classification of aerosols and the associated role they play in the atmospheric energy budget that directly ties them to the chemistry and circulation structure of the atmosphere.