Astronomers have proposed a new method to detect exoplanet atmospheres by analyzing rainbows and solar glints. This technique relies on the upcoming NASA Habitable Worlds Observatory (HWO) telescope, which is scheduled for launch in the early 2040s.
The HWO will feature a mirror at least six meters in diameter and an onboard polarimeter. While the telescope will not provide direct images of rainbows, it will detect specific optical phenomena. When an exoplanet is in a crescent phase, a solar glint from a liquid surface will create a measurable brightness spike, indicating the presence of an atmosphere.
The polarimeter will identify polarized light caused by light refraction in raindrops. By measuring the degree of polarization, scientists can determine the size of these droplets and the composition of the liquid. The study, published in the Monthly Notices of the Royal Astronomical Society, suggests this data will reveal the makeup of clouds and rain across vast distances.
Additionally, the telescope will observe Rayleigh scattering, where gas molecules polarize starlight at a 90-degree angle. Simulations indicate that these polarization signals will be detectable for a significant portion of nearby rocky exoplanets, helping HWO identify potentially habitable worlds orbiting sun-like stars.
