Compare sequential and simultaneous H2O–O2 characterization

Determine whether it is more efficient for Habitable Worlds Observatory surveys to obtain an initial yes-or-no detection of atmospheric H2O and O2 followed by separate abundance-characterization observations, or to seek robust simultaneous measurements of both molecules in a single observational program.

Background

The proposed strategy characterizes H2O and O2 simultaneously in the visible wavelength range after detection and orbit measurement. Simultaneous characterization requires higher signal-to-noise than H2O-only characterization and therefore may reduce the number of planets that can be surveyed.

The unresolved comparison is between a lower-cost preliminary molecular detection followed by targeted re-observation and a more expensive initial observation designed to measure both molecules robustly. The answer affects whether dual characterization should replace H2O-only characterization in the initial discovery survey.

References

Investigation is necessary to determine whether it is more efficient to seek a yes/no observation of \ce{H2O} and \ce{O2} and re-observe to characterize the molecules, or to immediately seek robust observation to measure abundances of both molecules simultaneously.

— Possible Observational Survey Strategies to Maximize Exoplanet Yields: A Report from the Survey Strategies Task Group in the Exoplanet Science Yields Working Group  (2609.25540 - Latouf et al., 22 Sep 2026) in Section 2.2, “Detection → Orbit Measurement → Characterization of H2O and O2 simultaneously”