Surveying Ultra-hot Jupiters using Phase Curves with $\textit{Twinkle}$

TL;DR

The paper tackles how to characterize ultra-hot Jupiters (UHJs) through comprehensive phase-curve observations by forecasting a Twinkle-based survey. It introduces a physically motivated model that combines thermal emission, reflected light, and stellar secondary effects across optical and infrared wavelengths, applied to 14 UHJs (and spectroscopic phase curves for WASP-189b). The results indicate Twinkle can detect all phase-curve signals in the survey and enable simultaneous optical–IR constraints on day–night temperatures, hotspot offsets, and atmospheric chemistry features such as $H_2O$, $CO$, and $CO_2$, informing 3D atmospheric dynamics and chemistry. This survey would provide the first population-wide, multi-wavelength UHJ phase-curve dataset and serve as a crucial precursor to, and complement for, JWST follow-up observations, enhancing our understanding of extreme exoplanetary atmospheres.

Abstract

Due to their high equilibrium temperatures ($T_{eq}$ $>$ 2000 K), ultra-hot Jupiters (UHJs) are the best characterized exoplanets to date. However, many questions about their formation, evolution, and atmospheres remain unanswered. Phase curve observations can reveal answers to these questions by constraining multiple atmospheric properties including circulation, albedo, and chemistry. To this end, we simulate and forecast a survey of UHJ atmospheres via phase curve observations with the upcoming $\textit{Twinkle}$ mission. $\textit{Twinkle}$ is a spectroscopic satellite covering 0.5--4.5 micron with a spectral resolving power of R $\sim$ 50--70. Using a physically motivated model, we simulate white-light photometric phase curve observations for 14 UHJs in $\textit{Twinkle's}$ field of regard. We project that $\textit{Twinkle}$ will be able to detect all phase curve signals in our survey. Additionally, we simulate spectroscopic phase curves for the UHJ, WASP-189b. From our simulated spectroscopic phase curves, we generate mock phase-resolved emission spectra. Previously detected UHJ molecules (e.g. H$_2$O, CO and CO$_2$) produce notable features in the resulting spectra, allowing for detailed atmospheric characterization to study the 3D structure of UHJ atmospheric chemistry and dynamics. For planets with hotspot phase offsets, $\textit{Twinkle}$ will be capable of detecting them both in the optical and infrared wavelength ranges. This future survey would represent the first UHJ phase curve survey with simultaneous coverage in optical and infrared wavelengths and will provide new constraints and reveal intriguing trends in these extreme environments.

Figures (1)

• Figure 1: Diagram of our full phase curve model described by Eq. \ref{['eq:fullphasecurve']}. $\phi$ represents the angle between the observer's line of sight (at phase 0) and the phase at which the planet is at. The planet is split up into M longitudinal slices and each slice is represented by a number, i.