To understand where the measured flux from the planet is coming from we need to capture both reflected and thermal components of the light from the planet. This requires broad wavelength coverage from <0.5 to >1 micron. Predicted planetary reflected signal vs. thermal emission for archetypal planets (letters correspond to planet properties shown in the inset plot) identified by Mayorga et al. (2019). Top: the total planetary flux as measured in flux units. Bottom: the percent contribution of reflected light to the total flux as a function of wavelength (R 300). Colored bands in the top panel show the photometric (hashed) and spectroscopic (solid) coverage from current and future facilities over this wavelength range. Figure courtesy of L. C. Mayorga. — astro-ph.EP
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.
Hannah R. Wakeford, Laura C. Mayorga, Joanna K. Barstow, Natasha E. Batalha, Ludmila Carone, Sarah L. Casewell, Theodora Karalidi, Tiffany Kataria, Erin M. May, Michiel Min
Comments: Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology SCDD, to be presented at HWO2025 and submitted to Astronomical Society of the Pacific following community comments. Feedback welcomed
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2506.22839 [astro-ph.EP] (or arXiv:2506.22839v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.22839
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Submission history
From: Hannah R Wakeford
[v1] Sat, 28 Jun 2025 10:40:20 UTC (1,037 KB)
https://arxiv.org/abs/2506.22839
Astrobiology,