Investigating HWO capabilities needed to rule out waterworld oxygen biosignature false positives

Molecular oxygen is a widely studied biosignature because of its association with photosynthetic life, and the apparent low likelihood of an O₂-rich atmosphere developing on a lifeless planet. However, abiotic O₂ may still be generated on habitable zone planets through several proposed evolutionary scenarios resulting in ‘false-positive’ biosignatures. One such scenario leads to an ocean-dominated planet, called a waterworld. These worlds are the evolutionary result of planets that have initial H₂O inventories exceeding ~50 Earth oceans. The pressure from such large surface water inventories increases the solidus of the silicate mantle and rapidly terminates crustal production. The cessation of crustal cycling removes geological oxygen sinks, and oxygen slowly builds up in the atmosphere via diffusion-limited escape of hydrogen. However, this false positive would be excluded by the detection of exposed land features, since there is a predictable maximum limit to topography based on the rushing strength of silicate rock. Based on this principle, we investigate the telescope capabilities needed to detect land using simulated reflected light retrievals of Earth-like and waterworld planets. Retrievals will be presented for a variety of land surface types and land fractions to determine the signal-to-noise, telescope aperture, wavelength range, and integration time required to exclude waterworld false positives with confidence. This builds on previous work that has demonstrated the retrieval of the red edge given sufficient signal-to-noise and spectral resolution, and directly informs the Habitable Worlds Observatory (HWO) capabilities required to identify waterworld false positives.