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Exoplanet LTT9779b – the largest mirror in the universe

Exoplanet LTT9779b – the largest mirror in the universe

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The plot shows exoplanet LTT9779b (right) orbiting its host star. © Ricardo Ramirez Reyes / Universidad de Chile / dpa

Titan falls as rain and the surface is 2,000 degrees hot. LTT9779b is a special sample of an exoplanet. “It’s a planet that shouldn’t exist,” says one researcher.

Marseille – Surrounded by clouds of reflective metal, the planet is the brightest exoplanet known to date. The European Space Agency, ESA, said that the superheated celestial body reflects 80 percent of the light falling on it from its star. For comparison: Venus, with its thick layer of clouds, reflects about 75% of the sunlight, while the Earth reflects only about 30%.

The exoplanet LTT9779b studied by the European space telescope “Khufu” is the size of Neptune and the “largest ‘mirror’ in the universe we know today”. A year on LTT9779b, i.e. one orbit of the star, lasts just 19 hours. Its reflective clouds are mostly made of silicates — the stuff that sand and glass are made of — mixed with minerals like titanium.

2000 degrees Fahrenheit

According to the research team led by Sergio Hoyer of the Marseille Astrophysical Laboratory, the side of the planet facing the star is hot by about 2,000 degrees — any temperature above 100 degrees is too hot to form water clouds.

Its glow isn’t the only amazing thing about LTT9779b, they said. Its size and temperature make it called a superhot Neptune – never before has Neptune been found so close to its star. “It’s a planet that shouldn’t exist,” said co-author Vivian Parmentier of the Observatoire de la Côte d’Azur. Experts hypothesized that as planets approach, all of their atmosphere usually blows away, leaving only bare rock.

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Hoyer explained that it may have been its metallic clouds that prevented the planet from evaporating. Additionally, the atmosphere’s high metallic content makes it difficult to blow away. The team’s findings are published in the journal Astronomy & Astrophysics.

Most planets reflect only a small part of the light from their star, ESA said. Either because they have an atmosphere that absorbs a lot of light, or because their surface is opaque or rough. The exceptions are frozen ice worlds or planets like Venus with a reflective cloud layer.

Khufu is a joint mission between the European Space Agency and Switzerland, led by the University of Bern in collaboration with the University of Geneva. The telescope detects exoplanets, that is, planets orbiting other stars. dpa