By Will Dunham
WASHINGTON (Reuters) – It’s a planet that astronomers say probably shouldn’t even exist.
Researchers said Monday they’ve seen a really extreme planet outside our solar system, a red-hot world a little bigger than Neptune that orbits a sun-like star every 19 hours and appears to be wrapped in metallic clouds made of titanium and silicates that bounce off. most of the incident light back into space.
“It’s a giant mirror in space,” said astronomer James Jenkins of Diego Portales University and the Center for Excellence in Astrophysics and Associated Technologies (CATA) in Chile, a co-author of the study published in the journal Astronomy & Astrophysics.
It reflects about 80% of the incoming light, making it the most reflective object known in the universe. Venus, the brightest object in Earth’s night sky next to the moon, is our solar system’s most reflective object, shrouded in toxic clouds of sulfuric acid. Venus reflects about 75% of the incoming light. The earth reflects about 30%.
Named LTT9779b, the planet and its star are located in our Milky Way galaxy about 264 light-years from Earth toward the constellation Sculptor. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).
The planet’s diameter is about 4.7 times larger than Earth’s, and it orbits very close to its star – closer than the distance of our solar system’s inner planet Mercury to the Sun and 60 times closer than the orbit of the earth. With blistering solar radiation from its star, its surface temperature is about 3,270 degrees Fahrenheit (1,800 degrees Celsius), hotter than molten lava.
With its star so close, the researchers say it’s a miracle it has any atmosphere. An atmosphere with water-based clouds, like on Earth, would have been blown away by solar radiation long ago. But they believe the clouds are made of metal, a combination of titanium and silicate — the stuff that makes up most of the rocks in the Earth’s crust.
“We even think the clouds may condense into droplets and titanium rain falls into parts of the atmosphere,” Jenkins said.
The researchers studied the planet using the CHEOPS telescope in orbit.
“No other planet like this has been discovered so far,” said astronomer and lead author of the study Sergio Hoyer of the Marseille Astrophysics Laboratory in France.
Possessing an atmosphere as it orbits so close to its star makes it “a planet that shouldn’t exist,” said astronomer and co-author Vivien Parmentier of France’s Côte d’Azur Observatory.
“The super-reflective cloud cover probably helped keep the planet from heating up too much and stripping it of its atmosphere,” Parmentier said. “This is quite unique because all the other planets at this temperature that are large enough to hold their atmospheres are too hot to form clouds and so are as dark as charcoal.”
It also appears to be tidally locked to its star as the Moon is to Earth, with a permanent day side facing the star and a permanent night side facing the star.
All previously known planets orbiting their stars in less than one Earth day were either “hot Jupiters,” gas giants similar in composition to our solar system’s largest planet, but much hotter due to solar radiation — or rocky planets that are smaller than Earth and have no atmosphere. .
The researchers wonder if LTT9779b, classified as an “ultra-hot Neptune,” may have started out as a gas giant and then lost most of its atmosphere, or if it started at its current size.
More than 5,000 extrasolar planets – called exoplanets – have been discovered, many with properties vastly different from the eight planets of our solar system. With increasingly capable instruments coming online – the James Webb Space Telescope became operational last year and the Extremely Large Telescope is under construction in Chile – more discoveries await.
“The diversity of exoplanets is astounding,” Parmentier said, “and we’ve just scratched the surface.”
(Reporting by Will Dunham, editing by Rosalba O’Brien)