Scientists puzzled by a ‘mirror’ planet in which it rains titanium and that should not exist

2023-07-15 04:36:41

There is a planet 260 light-years from here where it rains droplets of titanium that reflect light so much that this world shines at the same level as Venus, the brightest object in our sky second only to the Moon. However, this ‘mirror’ world should not exist: it is so close to its star that the theory says that it should not form clouds or have an atmosphere. But that’s the way it is, according to data collected by the Cheops space telescope. Scientists are baffled by the finding, which they give more information about in a publication in the journal ‘Astronomy and Astrophysics‘.

This strange exoplanet reflects 80% of the light from the star it orbits, an incredible amount without taking into account that Earth only manages 30% of it. Discovered in 2020, this Neptune-sized planet is called LTT9779b and it orbits its star in just 19 hours. Due to this proximity, the temperature of its illuminated face rises to 2,000 degrees, a temperature considered too high for clouds to form. However, the reflectivity of LTT9779b indicates its presence. “It was really an enigma,” according to Vivien Parmentier, a researcher at the Côte d’Azur Observatory (France) and co-author of the study.

The researchers considered the formation of these clouds “in the same way that condensation occurs in a bathroom after a hot shower,” explains the expert in a statement. Like the effect of very hot water in a bath, a burning stream of metal and silicate—the stuff glass is made of—supersaturates LTT9779b’s atmosphere until metallic clouds form.

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

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

In addition, the astronomers did not expect to find any type of atmosphere on this exoplanet due to its proximity to the star, which normally “drags” any type of gaseous formation.

After much research they found the explanation: “the metallic clouds of LTT9779b act like a mirror”, reflecting light and preventing the atmosphere from disintegrating, according to Maximilian Guenther, chief scientist of the Cheops project at the European Space Agency (ESA). They act “a bit like a shield” like the ones that protect “spaceships in old ‘Star Trek’ episodes,” he told AFP.

This research marks “an important step” because it shows how a planet the size of Neptune can survive in such an environment, the scientist added.

ESA’s Cheops telescope was sent into space in 2019 to explore the discovered planets outside the Solar System. He measured the reflective power of LTT9779b by comparing the light before and after the exoplanet disappeared behind its star.