A burning world where metallic clouds rain down drops of titanium that act “like a mirror”. LTT9779b, the brightest planet ever detected outside our solar system has revealed its face to astronomers, according to a study published on Monday. This strange exoplanet, located more than 260 light-years from Earth, reflects 80% of the light from its host star, according to new observations from the European space telescope Cheops (CHaracterising ExOPlanet Satellite).
It is the first exoplanet to match the brightness of Venus, the brightest object in our night sky except for the Moon. Discovered in 2020, this Neptune-sized star revolves around its star in just 19 hours.
Like “in a bathroom after a hot shower”
Due to this proximity, its illuminated face rises to 2,000 degrees, a temperature considered too high for clouds to form. However, the reflectivity of LTT9779b indicated the presence of clouds. “It was really an enigma”, according to Vivien Parmentier, researcher at the Côte d’Azur Observatory and co-author of a study published in the journal Astronomy and Astrophysics. The researchers then “considered the formation of these clouds in the same way that condensation occurs in a bathroom after a hot shower”, explains the researcher. A burning current of metal and silicate – the material from which glass is made – supersaturated LTT9779b’s atmosphere until metallic clouds formed.
But the planet had other surprises in store. To date, the only exoplanets known to circle their star so quickly (in less than 24 hours) are either gas giants 10 times larger than the Earth, or rocky planets half the size. Gold LTT9779b is about five times the size of the Earth and is located in an area that astronomers call “hot Neptune desert”, where planets of this size “should not exist”, summarizes Vivien Parmentier.
“A shield” like those that protect “Star Trek ships”
Moreover, astronomers expected such a planet to “see its atmosphere swept away by its star” to which it is so close, “leaving bare rock behind”. They found the explanation: “The metallic clouds of LTT9779b act like a mirror”, reflecting light and preventing the atmosphere from being blown away, according to Maximilian Guenther, chief scientist of the European Space Agency (ESA) Cheops project. . They act “a bit like a shield” like those that protect “spaceships in old episodes of the Star Trek series”, he said. By showing how a planet the size of Neptune can survive in such an environment, this research marks “an important step”, added the scientist.
ESA’s Cheops 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 the light before and after the exoplanet disappeared behind its star.