'Like a Mirror,' Astronomers Discover Extremely Reflective Planet 260 Light Years From Earth

The most reflective planet yet discovered outside of our Solar System is a blistering hot globe where metal clouds rain titanium droplets, according to astronomers on Monday.

According to fresh findings from Europe's exoplanet-probing Cheops satellite telescope, this odd world, which is more than 260 light years from Earth, reflects 80 percent of the light from its home star.

That makes it the first exoplanet with a radiance comparable to Venus, the brightest object in our night sky other than the Moon.

LTT9779b, a Neptune-sized planet found in 2020, circles its star in just 19 hours.

Because it is so near to its star, the side of the planet facing it is a scorching 2,000 degrees Celsius, which is far too hot for clouds to develop.

LTT9779b, on the other hand, appears to have them.

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

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

A sizzling torrent of metal and silicate – the substance of which glass is created – oversaturated LTT9779b's atmosphere to the point that metallic clouds developed, he added.

Getting across the 'Neptune desert'

In other aspects, the planet, which is roughly five times the size of Earth, is an exception.

The only previously discovered exoplanets that circle their sun in less than 24 hours are either gas giants 10 times the size of Earth or rocky planets half its size.

However, LTT9779b resides in an area known as the "Neptune desert," where planets of its size are not expected to be discovered.

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

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

According to the European Space Agency's Cheops project scientist Maximilian Guenther, the planet's metallic clouds "act like a mirror," reflecting light and preventing the atmosphere from being blown away.

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

According to him, the study is a "major milestone" since it demonstrates how a Neptune-sized planet may exist in the Neptune desert.

In 2019, the European Space Agency deployed the Cheops space telescope into Earth orbit on a mission to examine planets identified outside our Solar System.

It calculated LTT9779b's reflectiveness by comparing the light before and after the exoplanet vanished behind its star.