Can astronomers detect exoplanet oceans?
Given the plethora of confirmed exoplanets, many researchers have turned their attention to studying these strange new worlds in greater detail. With several exoplanets thought to orbit in the “habitable zone” of their host star where liquid water might be stable, different methods of detecting surface water are under development. One such proposed method of detecting water oceans on an exoplanet is via specular reﬂection, also known as “glint”. If you've seen a bright reflection of sunlight on a lake or ocean here on Earth, you've seen an example of the glint effect.
Scientists posit that surface oceans of exoplanets would affect the planet’s apparent reflectivity, also known as albedo. This increase of albedo should be detectable during the crescent phase of a planet.
In this model, astronomers don’t need to see the entire “disk” of a planet, where the planet is reflecting light like a full Moon from our point of view. Instead, they can detect reflected starlight in a planet’s gibbous phase, where we see only a part of the entire “full Moon” light. It is even possible to view an exoplanet in a crescent phase, where just a small sliver of reflected light is visible.