By Will Dunham
WASHINGTON (Reuters) – This is a planet that astronomers say probably shouldn’t even exist.
Researchers said on Monday they had spotted a truly extreme planet beyond our solar system, an extremely hot world slightly larger than Neptune that orbits a sun-like star every 19 hours and appears to be shrouded metallic clouds made of titanium and silicates that reflect most of the incoming light back into space.
“It’s a giant mirror in space,” said astronomer James Jenkins of Diego Portales University and the Center of Excellence in Astrophysics and Associated Technologies (CATA) in Chile, co-author of the published research. in the journal Astronomy & Astrophysics.
It reflects about 80% of incoming light, making it the most reflective object known in the universe. Venus, the brightest object in Earth’s night sky after the moon, is the most reflective object in our solar system, coated in clouds of toxic sulfuric acid. Venus reflects about 75% of incoming light. The Earth reflects about 30%.
The planet, named LTT9779b, and its star are located in our Milky Way galaxy about 264 light-years from Earth in the direction of the constellation Sculptor. A light year is the distance light travels in one year, 5.9 trillion miles (9.5 trillion km).
The planet’s diameter is about 4.7 times larger than Earth, and it orbits very close to its star – closer than the distance of our solar system’s innermost planet Mercury to the sun and 60 times closer than Earth’s orbit. With its star’s blazing solar radiation, its surface temperature is about 3,270 degrees Fahrenheit (1,800 degrees Celsius), hotter than molten lava.
With its star so close, it’s a wonder it has any atmosphere, the researchers say. An atmosphere with water-based clouds, like on Earth, would have been swept away by solar radiation a long time ago. But they think its clouds are metallic, a combination of titanium and silicate – the stuff that makes up most rocks in the earth’s crust.
“We even think the clouds could condense into droplets and drop titanium rain into parts of the atmosphere,” Jenkins said.
The researchers studied the planet using the European Space Agency’s CHEOPS orbiting telescope.
“No other planet like this has been discovered to date,” said astronomer and lead study author Sergio Hoyer of the Marseille Astrophysics Laboratory in France.
Having an atmosphere orbiting so close to its star makes it “a planet that shouldn’t exist”, according to astronomer and study co-author Vivien Parmentier of the Côte d’Azur Observatory in France.
“The super-reflective cloud cover likely helped keep the planet from overheating and being stripped of its atmosphere,” Parmentier said. “It’s quite unique because all the other planets at this temperature that are large enough to hold their atmosphere are too hot to form clouds and are therefore as dark as charcoal.”
It also appears to be tidally locked to its star like the moon is to Earth, with a permanent day side facing the star and a permanent night side facing outward.
All previously known planets that orbit their stars in less than one Earth day were either “hot Jupiters”, gas giants similar in composition to the largest planet in our solar system but much hotter due to solar radiation – or rocky planets smaller than Earth and devoid of atmosphere.
Researchers wonder if LTT9779b, classified as “ultra-hot Neptune”, may have started out as a gas giant only to lose most of its atmosphere, or if it started out at its current size.
More than 5,000 planets beyond our solar system – called exoplanets – have been discovered, many of which have very different characteristics from the eight planets in our solar system. With more and more 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 staggering,” Parmentier said, “and we’ve just scratched the surface.”
(Reporting by Will Dunham, editing by Rosalba O’Brien)