A planet surrounded by reflective metallic clouds is the most luminous exoplanet known to date. The ultra-hot celestial body reflects a whopping 80 percent of the light falling on it from its star, said the European space agency Esa. For comparison: Venus, with its thick layer of clouds, reflects around 75 percent of the sunlight, while Earth only reflects around 30 percent.
The exoplanet LTT9779b studied with the European space telescope “Cheops” is about as big as Neptune and “the largest ‘mirror’ in the universe that we know today”. A year on LTT9779b, i.e. one orbit of the star, lasts only 19 hours. Its reflective clouds are mostly made of silicate – the stuff that makes up sand and glass – mixed with metals like titanium.
2000 degrees hot
According to the research team led by Sergio Hoyer from the Marseille Astrophysics Laboratory, the star-facing side of the planet is about 2000 degrees hot – any temperature above 100 degrees is too hot for water clouds to form.
Its glare isn’t the only surprising thing about LTT9779b, they said. Its size and temperature make it a so-called ultra-hot Neptune – never before has one been found so close to its star. “It’s a planet that shouldn’t exist,” said co-author Vivien Parmentier of the Observatoire de la Côte d’Azur. Experts assumed that with planets that close, all of the atmosphere was usually blown away, leaving only bare rock.
Hoyer explained that it was probably his metal clouds that prevented the planet from evaporating. In addition, the high metal content of the atmosphere makes it difficult for it to be blown away. The team’s results are published in the journal “Astronomy
Most planets reflect only a small fraction of the light coming from their star, Esa said. Either because they have an atmosphere that absorbs a lot of light, or because they have a dark or rough surface. Exceptions are frozen ice worlds or planets like Venus with a reflecting cloud layer.
“Cheops” is a joint mission of ESA and Switzerland led by the University of Bern in cooperation with the University of Geneva. The telescope observes exoplanets, i.e. planets orbiting other stars.
