Continuous Habitable Zone Metric for Prioritizing Habitable Worlds Observatory Targets
Future direct imaging space telescopes, such as NASA’s Habitable Worlds Observatory (HWO), will be the first capable of both detecting and characterizing terrestrial exoplanets in the habitable zones (HZ) of nearby Sun-like stars.
Since this will require a significant amount of time and resources for even a single system or exoplanet, the likelihood that a system will host detectable life should be considered when prioritizing observations. One method of prioritization is to estimate the likelihood that an exoplanet has remained continuously within the HZ long enough for life to emerge and make a detectable impact on the atmosphere.
We utilize a Bayesian method to calculate the likelihood that a given orbital radius around a star is currently in the 2 Gyr continuous habitable zone (CHZ2), the approximate time it took life on Earth to significantly oxygenate the atmosphere.
We apply this method to the 164 stars in the NASA Exoplanet Exploration Program Mission Star List (EMSL) for HWO, representing a preliminary sample of Sun-like stars with HZs most accessible to a future direct imaging mission. By considering the CHZ2 likelihood at all orbital radii outside a hypothetical inner working angle for HWO, we define a metric for prioritizing targets according to the accessibility and total extent of the CHZ2.
We find that the CHZ2 metric peaks between 3−4 Gyr for late-F and early-G dwarfs, but tentatively determine that stars earlier than ∼F3 or hotter than ∼6600 K are unlikely to have a CHZ2 at the time of observation.
Austin Ware, Patrick Young
Comments: 22 pages, 7 figures, 4 tables, accepted to ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2505.20558 [astro-ph.EP] (or arXiv:2505.20558v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2505.20558
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Submission history
From: Austin Ware
[v1] Mon, 26 May 2025 22:44:03 UTC (5,163 KB)
https://arxiv.org/abs/2505.20558
Astrobiology,
