The Science Potential of Characterizing Gas Giant Exoplanets with HWO
Abstract
With the ability to directly image Earth-like exoplanets and search their atmospheres for biosignatures, the upcoming Habitable Worlds Observatory (HWO) will also collect high signal-to-noise ratio (S/N) reflected-light photometry and spectra of nearby gas giant exoplanets. Such high-quality data would allow novel investigations into gas giant atmospheric composition, formation, and kinematic properties, and could enable the detection of exomoons around these planets. We use the EXOSIMS direct imaging mission simulator to model HWO observations of Jupiter-radius gas giants at Earth-like and Jupiter-like instellations around the 164 stars in the ExEP target list. We find that HWO should be able to achieve S/N ≥ 5 broadband visible-light detections of gas giants in this instellation range within 5 minutes of integration. 10 hours of R=1000 near-IR spectroscopy with HWO should reveal water, methane, and ammonia absorption features in the atmospheres of Jupiter-like gas giants. HWO time-series photometry should exceed 1% flux precision in one hour for any Earth-instellation gas giants around ExEP stars, and for Jupiter-like gas giants at d≤ 7 parsecs. Time-series light curves at this cadence and precision could, over tens of hours, reveal rotation-induced variability comparable to Jupiter's. Eclipses of Mars-sized exomoons may be detectable in high-cadence light curves of Jupiter sized planets in the habitable zones of ExEP stars at d≤ 10 parsecs. For any hypothetical Earth-like exomoons with oxygen-rich atmospheres at d≤ 7 parsecs from the Solar System, HWO might be able to detect the spectral signature of molecular oxygen amid the parent planet's photon noise in deep (∼400 hour integration) spectroscopic HWO observations at R=1000. Such moons, if they exist, represent additional habitable worlds that HWO could investigate for biosignatures.
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BibTeX
@misc{dacus2026science,
title = {{The Science Potential of Characterizing Gas Giant Exoplanets with HWO}},
author = {Beck Dacus and Jean-Baptiste Ruffio and Quinn Konopacky and Renyu Hu and Tyler D. Robinson and Mary Anne Limbach and Kielan Hoch and Katelyn Horstman and Bruce Macintosh and Dimitri Mawet and Michael W. McElwain and Bertrand Mennesson and Charley Noecker and Marshall D. Perrin and Laurent Pueyo and Dmitry Savransky and Corey Spohn and Sarah Steiger and Connor Vancil and Ji Wang and Nicole Wolff and Shelley Wright},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.22653},
eprint = {2609.22653},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.22653},
}
RIS
TY - UNPB
TI - The Science Potential of Characterizing Gas Giant Exoplanets with HWO
AU - Beck Dacus
AU - Jean-Baptiste Ruffio
AU - Quinn Konopacky
AU - Renyu Hu
AU - Tyler D. Robinson
AU - Mary Anne Limbach
AU - Kielan Hoch
AU - Katelyn Horstman
AU - Bruce Macintosh
AU - Dimitri Mawet
AU - Michael W. McElwain
AU - Bertrand Mennesson
AU - Charley Noecker
AU - Marshall D. Perrin
AU - Laurent Pueyo
AU - Dmitry Savransky
AU - Corey Spohn
AU - Sarah Steiger
AU - Connor Vancil
AU - Ji Wang
AU - Nicole Wolff
AU - Shelley Wright
PY - 2026
DA - 2026/09/18
PB - arXiv
DO - 10.48550/arxiv.2609.22653
UR - https://arxiv.org/abs/2609.22653
AB - With the ability to directly image Earth-like exoplanets and search their atmospheres for biosignatures, the upcoming Habitable Worlds Observatory (HWO) will also collect high signal-to-noise ratio (S/N) reflected-light photometry and spectra of nearby gas giant exoplanets. Such high-quality data would allow novel investigations into gas giant atmospheric composition, formation, and kinematic properties, and could enable the detection of exomoons around these planets. We use the EXOSIMS direct imaging mission simulator to model HWO observations of Jupiter-radius gas giants at Earth-like and Jupiter-like instellations around the 164 stars in the ExEP target list. We find that HWO should be able to achieve S/N ≥ 5 broadband visible-light detections of gas giants in this instellation range within 5 minutes of integration. 10 hours of R=1000 near-IR spectroscopy with HWO should reveal water, methane, and ammonia absorption features in the atmospheres of Jupiter-like gas giants. HWO time-series photometry should exceed 1% flux precision in one hour for any Earth-instellation gas giants around ExEP stars, and for Jupiter-like gas giants at d≤ 7 parsecs. Time-series light curves at this cadence and precision could, over tens of hours, reveal rotation-induced variability comparable to Jupiter's. Eclipses of Mars-sized exomoons may be detectable in high-cadence light curves of Jupiter sized planets in the habitable zones of ExEP stars at d≤ 10 parsecs. For any hypothetical Earth-like exomoons with oxygen-rich atmospheres at d≤ 7 parsecs from the Solar System, HWO might be able to detect the spectral signature of molecular oxygen amid the parent planet's photon noise in deep (∼400 hour integration) spectroscopic HWO observations at R=1000. Such moons, if they exist, represent additional habitable worlds that HWO could investigate for biosignatures.
ER -