First observation of a 'rainbow' on an exoplanet.

The CHEOPS space telescope has detected concentric rings of light with rainbow colors on WASP-76b, an exoplanet that rains iron.

Simulation of exoplanet WASP-76b and its rainbow-like halo in the atmosphere. Image: ATG/ESA. — Simulation of exoplanet WASP-76b and its rainbow-like halo in the atmosphere. Image: *ATG/ESA.*

Astronomers have for the first time discovered evidence of a halo, a colorful, rainbow-like meteorological phenomenon, on an exoplanet (a planet outside our solar system), IFL Science reported on April 5. The new research was published in the journal Astronomy & Astrophysics.

A halo consists of concentric rings of light with rainbow colors – red on the outside and violet on the inside. Although also formed by water droplets bending light, a halo differs from a rainbow because the scattered light is diffracted between the water droplets, rather than refracted as it passes through them. The phenomenon is named as such because it resembles the halos around the heads of saints in medieval paintings.

"There's a reason why the halo has never been seen outside the Solar System before. This phenomenon requires very special conditions. First, it needs atmospheric particles that are nearly perfectly spherical, completely uniform, and stable enough to be observed for extended periods. The star near the planet needs to shine directly on it, and the observing instrument – in this case, the CHEOPS space telescope – needs to be pointed in the right direction," said Olivier Demangeon, lead researcher and astronomer at the Institute of Astrophysics and Space Sciences in Portugal.

The exoplanet WASP-76b is so close to its host star that it is thought to rain iron. This close proximity means one side of WASP-76b is tidally locked and always faces the host star, known as the "day side," which reaches temperatures of 2,400 degrees Celsius. The other side of the exoplanet, the "night side," always faces out into space and is cooler, but is subject to strong winds caused by the temperature difference. Near the day-night boundary, the metal vaporizing on the day side condenses and falls as iron rain.

Further evidence is needed to confirm that the phenomenon observed by the CHEOPS space telescope at WASP-76b is a rare halo. If true, this phenomenon indicates the presence of clouds composed of perfectly spherical water droplets that have existed for at least three years, or that these clouds are continuously replenished. If the clouds are long-lasting, the atmospheric temperature of WASP-76b must also have remained stable over time. This is interesting information, suggesting stability on an exoplanet considered to be chaotic.

The new findings also suggest that exoplanet experts could study distant worlds to find similar light phenomena, including starlight reflecting off lakes and liquid oceans. This is crucial to the ongoing human search for life beyond our solar system.

Thu Thao (According to Space, IFL Science )

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