The brightest exoplanet discovered by astronomers

A burning world where metal clouds shower droplets of titanium, which act “like a mirror”: The brightest planet ever discovered outside our solar system has revealed its face to astronomers, according to a study published Monday.

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This strange exoplanet, located more than 260 light-years from Earth, reflects 80% of the light of its host star, according to new observations from the European space telescope Khufu (distinguishes the exoplanet satellite).

It is the first exoplanet to match the brightness of Venus, and it is the brightest object in our night sky except for the Moon. Discovered in 2020, this Neptune-sized planet, called LTT9779b, orbits its star in just 19 hours.

Because of this proximity, its luminous face rises to 2,000 degrees, a temperature considered too high for clouds to form. However, the reflection of LTT9779b indicates the presence of clouds.

“It was really a mystery,” according to Vivian Parmentier, a researcher at the Côte d’Azur Observatory and co-author of a study published in the journal Astronomy & Astrophysics. Then, “the researchers looked at the formation of these clouds in the same way that condensation occurs in the bathroom after a hot shower,” the researcher explained in a press release.

Like the effect of very hot water in a shower, the burning stream of metal and silicates—the material glass is made of—saturated LTT9779b’s atmosphere until metallic clouds formed.


But the planet had other surprises in store. To date, the only exoplanets known to orbit their star very quickly (in less than 24 hours) are either gas giants 10 times larger than Earth or rocky planets half the size of Earth.

LTT9779b gold is about five times the size of Earth and is located in an area astronomers call the “hot Neptune desert,” where planets of this size “shouldn’t exist,” concludes Mr. Parmentier.

Moreover, astronomers expected that such a planet would “see its atmosphere swept away by its star” to which it is so close, “leaving bare rock behind.”

They found the explanation: LTT9779b’s “metallic clouds act like a mirror,” reflecting light and preventing the atmosphere from being blown away, according to Maximilian Guenther, chief scientist for the European Space Agency’s (ESA) Khufu project.

They act “shield-like” like those protecting the “spaceships” in older episodes of the series Star TrekHe told AFP.

The scientist added that by showing how a planet the size of Neptune can survive in such an environment, this research marks an “important step.”

The European Space Agency’s Khufu Space Telescope was sent in 2019 to characterize planets discovered outside our solar system. He measured the reflective power of LTT9779b using the transit method, which involves comparing light before and after the exoplanet disappeared behind its star.

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