Astronomers discover most reflective planet that's 'like a mirror'

Astronomers said on Monday (July 10) that a scorching hot world where metal clouds rain titanium is the most reflective planet ever observed outside our solar system. This fascinating and strange world is more than 260 light years away from Earth. It reflects 80 per cent of the light it gets from its host star. The observations have been made by Europe's exoplanet-probing Cheops space telescope.

The discovery makes the exoplanet comparably shiny as Venus which is the brightest object in the night sky after the Moon.

The planet, first discovered in 2020, is the size of Neptune. This means it is considerably bigger than Earth. The planet has been called LTT9779b. It orbits its star in just 19 hours.

Because of its very close proximity to its star, the planet's side which faces the star has a temperature of 2000 degrees Celsius. This temperature is considered far too hot for clouds to form.

Yet LTT9779b seems to have them.

"It was really a puzzle," said Vivien Parmentier, a researcher at France's Cote d'Azur Observatory and co-author of a new study in the journal Astronomy and Astrophysics. Parmentier was quoted by AFP.

The researchers then "realised we should think about this cloud formation in the same way as condensation forming in a bathroom after a hot shower," he said in a statement.

Like running hot water steams up a bathroom, a scorching stream of metal and silicate -- the stuff of which glass is made -- oversaturated LTT9779b's atmosphere until metallic clouds formed, he said.

Surviving 'Neptune desert'

The planet, which is around five times the size of Earth, is an outlier in other ways.

But LTT9779b lives in a region called the "Neptune desert", where planets its size are not supposed to be found.

"It's a planet that shouldn't exist," Parmentier said.

"We expect planets like this to have their atmosphere blown away by their star, leaving behind bare rock."

The metallic clouds 'act like a mirror' and reflect away light, thus preventing the atmosphere from being blown away, as per Cheops project scientist Maximilian Guenther.

"It's a bit like a shield, like in those old Star Trek films where they have shields around their ships," he told AFP.