The brightest exoplanet ever found in our galaxy has clouds made of glass and titanium.

Called LTT-9779b and located 263 light-years away, this planet is so bright that it reflects 80 per cent of the light from its host star, almost like a mirror. This is even brighter than Venus, known for its high brightness, which reflects about three-quarters of the light falling on it.

And that's not all. The Neptune-sized world is scorching hot, with temperatures reaching 2,100 Kelvin (1,827 degrees Celsius or 3,320 Fahrenheit). This is the highest temperature ever seen on an exoplanet of this type.

"Imagine a burning world close to its star, clouds of heavy metals floating in the air, droplets of titanium raining down," says astronomer James Jenkins of Diego Portales University in Chile.

This remarkable discovery was made using the European Space Agency's CHaracterising Exoplanet Satellite (Cheops). The exoplanet and its orbit were initially found and characterised using other instruments, but Cheops took a longer and closer look to obtain an extremely detailed data set known as a phase curve.

As an exoplanet orbits a star, the amount of light emitted by the system changes. When the planet is in front of the star, the star's light is reduced, but the light is also reduced when the planet is behind the star. This is because the light it emits and reflects on both sides is added to the total light emitted by the system.

Astronomers can use this information to obtain how much light the exoplanet emits by subtracting the light emitted from the heat. This is how they obtained LTT-9779b's reflectivity, a measurement known as albedo. In this context, Earth's albedo is 0.3, reflecting 30 per cent of the sun's light. Venus has an albedo of 0.75.

However, LTT-9779b's atmosphere is strange. At such scorching temperatures, any atmosphere would be expected to basically boil away - even those with clouds of glass and metal. The researchers found that the presence of LTT-9779b indicates a supersaturation of these substances.

"To fill a bath with steam, you either cool the air until the water vapour condenses, or the air is so saturated with vapour that it can't hold any more, so you keep pouring hot water until clouds form," says astronomer Vivien Parmentier of the Côte d'Azur Observatory in France. "Similarly, LTT-9779b can form metallic clouds despite being very hot because the atmosphere is oversaturated with silicate and metal vapours."

Yet astronomers say that according to the models, this exoplanet "should not exist". This planet, with a radius 4.7 times that of Earth and 29 times the mass, orbits its Sun-like star in a 19-hour orbit. This places it in the 'hot Neptune desert'. We have found very few worlds like this one because they cannot withstand the X-ray and ultraviolet radiation from their stars.

Studies have shown that higher gravity may help LTT-9779b protect its atmosphere against intense stellar irradiation, but the new findings suggest a second retention mechanism.

"We believe that these metal clouds help the planet survive in the hot Neptune desert," says astrophysicist Sergio Hoyer of the Marseille Astrophysics Laboratory in France.

"The clouds reflect light and prevent the planet from getting too hot and evaporating. Meanwhile, being highly metallic makes the planet and its atmosphere heavy and difficult to blow away."

 

Source: https://www.sciencealert.com/