Astronomers find ultra-hot strange ‘mirror-like’ planet that ‘shouldn’t exist’

‘We expect planets like this to have their atmosphere blown away by their star’

Scientists have discovered an ultra-hot Neptune-like exoplanet with clouds made of metal vapour, making it the shiniest planet ever found.

The planet LTT9779 b according to the study published in the journal Astronomy & Astrophysics, reflects a whopping 80 per cent of the light shone on it – more than the reflection by Venus, which is the brightest known object in our night sky.

“It’s a planet that shouldn’t exist. We expect planets like this to have their atmosphere blown away by their star, leaving behind bare rock,” study co-author Vivien Parmentier said.

It was found close to its star, orbiting it in less than a day, data from the European Space Agency’s Cheops telescope revealed.

At such a close distance to its star, the planet’s atmosphere is estimated to reach around 2000°C, making it too hot for even clouds made of metal or glass to exist, say researchers, including those from Côte d’Azur Observatory in France.

“It was really a puzzle, until we realised we should think about this cloud formation in the same way as condensation forming in a bathroom after a hot shower,” Dr Parmentier said.

“To steam up a bathroom you can either cool the air until water vapour condenses, or you can keep the hot water running until clouds form because the air is so saturated with vapour that it simply can’t hold any more,” he explained.

Similarly, researchers say, LTT9779 b can form metallic clouds despite being so hot as its atmosphere is oversaturated with silicate and metal vapours.

The so called “ultra-hot Neptune” planet is also unique with no other planets of its size and mass found to orbit so close to their star.

The planet is about 4.7 times as big as Earth’s with a year on it taking just 19 hours, and its peculiar metal clouds may actually be helping it survive, researchers say.

“The clouds reflect light and stop the planet from getting too hot and evaporating. Meanwhile, being highly metallic makes the planet and its atmosphere heavy and harder to blow away,” Sergio Hoyer, another author of the study, added.

To determine the light-reflecting characteristics of the planet, scientists viewed it via the Cheops telescope as it moved behind its its host star.

They theorised that as the planet reflects light, when combined with its star, it is likely to send more light towards the space telescope right before the planet is out of view, than right after.

Scientists predicted that the difference in visible light received right before and after the planet is hidden would tell how much light the planet reflects.

“Precisely measuring the tiny change in signal from the star eclipsing the planet was only possible with Cheops,” Dr Hoyer added.