Astronomers have discovered the most reflective planet ever outside the solar system. An extremely hot exoplanet, or exoplanet, acts as a cosmic mirror because it is covered in reflective clouds of metal.
The planet, called LTT9779 b, is located about 264 light-years from Earth and reflects about 80% of the light that shines on it from its parent star. Compared to LTT9779 b, Earth reflects only 30% of the light that falls on it from the Sun. LTT9779 b is so hot and reflective that it’s the first exoplanet found to give the solar system’s brightest planet, Venus, a run for its money; Venus has a thick layer of clouds that reflect about 75% of the incident sunlight.
The exoplanet, in turn, is five times as wide as Earth, meaning it is the largest cosmic mirror ever discovered. “Imagine a world on fire, close to its star, with heavy clouds of metal floating aloft, raining titanium droplets,” said James Jenkins, co-author of the paper and University of Diego Portales astronomer. he said in a statement.
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While LTT9779 b was first detected by NASA’s Transiting Exoplanet Reconnaissance Mission (TESS) in 2020, the highly reflective nature of the world was not revealed until a follow-up procedure by the European Space Agency’s Exoplanet Search spacecraft, which characterizes the Moon. Industrial Exoplanets (CHEOPS). LTT9779 b is about the size of the solar system’s icy giant Neptune, which, along with its roasting temperature, classifies it as a superhot Neptune.
How LTT9779 b became a Neptune-sized celestial mirror
At first, LTT9779 b’s high reflectivity, a characteristic known as “albedo,” was a mystery to scientists. This is because most planets, other than icy worlds or planets with reflective cloud layers such as Venus, have a low percentage of albedos as a result of starlight being absorbed by the atmosphere or surfaces, thus preventing it from being reflected back into space.
LTT9779 b has been predicted to have a low albedo because, with a surface temperature of about 3,650 degrees Fahrenheit (2,000 degrees Celsius) on the side of the exoplanet that faces its star permanently, it must be too hot to form clouds of water. The high temperature should make the LTT9779 b too hot even for metal or glass drawing.
“It’s a planet that shouldn’t exist,” research co-author and observatory told Côte d’Azur researcher Vivian Parmentier. “We expect planets like this to have their atmospheres blown away by their star, leaving behind barren rocks.”
The existence of such a planet prompted the researchers to explore other theories for how these metallic clouds formed. “It was really a puzzle until we realized we should think of this cloud formation in the same way that condensation forms in the bathroom after a hot shower,” Parmentier added. “To steam a bath, you can either cool the air until the water vapor condenses, or you can keep the hot water running until clouds form because the air is too steamy to hold any longer.”
The team believes that LTT9779 b got its metallic clouds and high albedo when its atmosphere was saturated with silicates and metal vaporized by scorching temperatures on the planet’s perpetual day side.
However, the reflective nature of the LTT9779b is not its only exceptional quality. An exoplanet is also an example of a planetary type that has eluded astronomers for decades and remains a mystery.
Superhot Neptune is an example of the lost type of planet
As an extremely hot Neptune orbiting close to its star, LTT9779b is the first of the group of “lost planets” to be discovered. Planets of this size and mass, orbiting close to their parent stars, have long been absent from the exoplanet catalog, which now contains more than 6,000 worlds.
All other planets found so close to their parent star that they orbit it in less than a day were called “hot Jupiters” about ten times the width of Earth, or rocky worlds smaller than twice the size of our planet.
This left the absence of planets of similar sizes and masses between these classes in the closest location to their stars. Its absence has become known as the “hot Neptune desert” by scientists.
With a size slightly larger than the ice giant’s name and an orbit of 19 hours, LTT9779 b sits firmly in the gap.
The planet’s survival in the hot desert of Neptune, very close to its star, could be explained by its high reflectivity.
“We think these metallic clouds help the planet survive in the hot Neptune desert,” said the lead author of the paper and Marseille Astrophysical Laboratory said scientist Sergio Hoyer. “Clouds reflect light and prevent the planet from getting too hot and evaporating. At the same time, being so metallic makes the planet and its atmosphere heavy and difficult to blow away.”
LTT9779 b will likely be the focus of intense study over the coming years, as the exoplanet is a close target of observation for both the James Webb Space Telescope and the Hubble Space Telescope. This should allow scientists to better understand the atmosphere, clouds, and its other properties.
The team’s research is published in the journal Astronomy and astrophysics.
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