In the future, signatures of sunlight reflected in the oceans could help identify exoplanets covered by large bodies of water. This is what a study led by researchers at the Netherlands Meteorological Institute and Delft University of Technology proposes, who examined the signatures of light reflected by Earth's oceans and explored their flow and polarization.
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Today, there are scientific estimates that show that up to 25% of known exoplanets have oceans, but much of this water may be below their surface. In the Solar System, for example, only Earth has oceans on its surface, although several moons in our neighborhood have oceans below them. It is possible that this also happens with dwarf planets.
Some of the thousands of exoplanets already discovered must have oceans (Image: Reproduction/NASA/JPL-Caltech)
For now, we are not close to detecting oceans in the subsurface of exomoons (natural satellites of exoplanets), but the good news is that, with the advancement of technology, it may be possible to identify oceans on Earth-like worlds. “Numerical simulations of starlight reflected by Earth-like exoplanets predict signatures of habitability, which can be searched for by future telescopes,” the authors wrote.
They note that observations of liquid water oceans would only be possible through direct detection of starlight, reflected by the planet. So, for the study, they modeled two Earths: one would be a dry planet and the other a wet one, with clouds and atmosphere. Then they simulated how light would reflect off these worlds under different conditions.
During the numerical simulations, they calculated three different parameters and modeled the oceans considering that they are Fresnel reflecting surfaces (when the reflected light is in the same plane as the incident one), with waves, foam and wave shadows all present. over the water. In the end, the team discovered that only oceans can decrease the polarization of light in some ways.
Comparison of the degree of polarization of a star's light, reflected by dry, cloudless planets, and by worlds with cloudless oceans
Measuring the polarization of light in the oceans is important, because starlight alone should not be polarized. Furthermore, although light signals degrade with distance, this does not affect polarization. “Current telescopes on the ground and in space are unable to measure polarized light reflected by Earth-like exoplanets,” the authors noted.
This may change with future telescopes, such as the European Extremely Large Telescope (E-ELT) and the Large Ultraviolet Optical Infrared Surveyor (LUVOIR), from the European Southern Observatory and NASA, respectively. Both will be able to collect measurements of polarized light: the E-ELT is expected to begin operating in 2027 and will be able to detect starlight reflected by exoplanet oceans. Therefore, if the authors' simulations are correct, the detection of oceans on other worlds may not be far off.
The article with the results of the study was accepted for publication in the journal Astronomy and Astrophysics, and can be accessed in the arXiv repository, without peer review.
