Researchers from the University of Arizona propose detecting liquid oceans on Earth-like exoplanets by observing their specular reflection, or “glint.” Water reflects starlight like a mirror at shallow angles, making a planet appear brighter during its crescent phase. The effect has already been observed on Earth and in Titan’s hydrocarbon lakes, but never confirmed for an exoplanet.

The team adapted the rfast atmospheric retrieval tool with the Cox-Munk ocean model, including the effects of wind and waves. Simulations suggest it could distinguish ocean-bearing worlds at phase angles above 120 degrees, while atmospheric scattering would make the signal redder. The result could give the planned Habitable Worlds Observatory more observing flexibility, although clouds may hide the signal or imitate a glint.

https://www.universetoday.com/articles/nasas-next-great-observatory-could-spot-oceans-on-distant-worlds