Astronomers have discovered an Earth-sized planet that is bathed in so much radiation that its atmosphere has long since eroded away, leaving it bare. Life as we know it cannot exist in this turbulent world, but astronomers are interested in it for another reason: for the first time, they can study geology planets outside our solar system.
Newly discovered an exoplanet, named SPECULOOS-3 b, is a rocky planet approximately 55 light years from Earth. It orbits its star every 17 hours, but the days and nights on the planet are endless. Astronomers suspect that the planet is tidally bound to its star like the Moon is to Earth. The only day side always faces the star, while the night side is locked in eternal darkness.
Telescope observations show that frequent emission from the star of the exoplanet, a 7 billion red dwarf the size of Jupiter, roasts the planet to Venus-like temperatures. So any atmosphere the planet could have easily ripped into space long ago and left behind an airless, sizzling ball of rock, astronomers report in a new study published May 15 in the journal Astronomy of nature.
“Life as we know it could not have emerged on the surface of a planet—atmosphere or not—because it could not support large amounts of liquid water,” the study’s lead author Michael Gillon, an astronomer at the University of Liege in Belgium, told Live Science. “This is a planet that looks like bare rock Mercury.”
On the topic: James Webb telescope discovers one-of-a-kind atmosphere around ‘Hell Planet’ in distant star system
Although SPECULOOS-3 b is unfriendly to life, astronomers said it is close enough to Earth for detailed follow-up studies of its chemical composition, which will reveal whether the planet was once geologically active. Observations are already scheduled from James Webb Space Telescope (JWST), for example, will be able to confirm whether volcanic eruptions have occurred on the planet. This would reveal how rocky planets like SPECULOOS-3 b form around faint, light stars and whether some of them might be suitable for life despite being close to their stars.
The researchers “searched intensively” for planetary siblings of SPECULOOS-3 b in the same star system, but found none, Gillan said. He noted that these extra planets may exist, but they are too small or too far from their star to be seen.
A hot planet around a cold star
Gillan and his colleagues discovered SPECULOOS-3 b using a network of six telescopes spread across Chile, the Canary Islands and Mexico since 2011. This network is called the Search for Planets Eclipsing Ultra-Cool Stars, or SPECULOOS, which shares its name with the Belgian shortbread cookies that are traditionally given to children on December 6 for Saint Nicholas Day.
The main goal of the project is to discover rocky planets orbiting ultra-cool dwarf stars, whose tiny sizes make it easier for telescopes to detect orbiting planets. Besides being thousands of degrees cooler than the sun and hundreds of times dimmer, they burn their fuel slowly and end up living much longer, about 100 billion years. (The sun will be approximately 10 billion years old when it dies in about 4.5 billion years.)
“They are expected to be the last stars still shining in the universe,” study co-author Lobster Trioprofessor of exoplanetology at the University of Birmingham in England, said in a statement. Researchers say their ultra-long lifespans offer favorable windows for the emergence of life on planets in their systems.
However, their extreme weakness makes them difficult to study. To detect SPECULOOS-3 b, the SPECULOOS robotic telescope in Mexico continuously observed notable dips in light from the host star for five nights in 2021. According to the study, then there were the first hints of the new planet’s orbit, which were confirmed a year later.
“If there was no atmosphere, there would be no blue sky, no clouds – it would just be dark, like on the surface month,”” co-author of the study Benjamin Rackhamresearcher at the Massachusetts Institute of Technology, said in a separate MIT statement. “And the ‘Sun’ would be a large, crimson-red, spotted and bright star that would appear about 18 times larger than the sun appears to us in the sky.”
SPECULOOS-3 b is the ninth such planet found by the project, and the team expects to discover many more in the coming years, Gillan said. Like the planets previously discovered by the project — including a family of seven in the well-known TRAPPIST-1 system, some of which are considered potentially habitable — the new SPECULOOS-3 b “is an excellent target for JWST Gillan said.
“With such a world, we could start doing exoplanetary geology,” the study co-author Julien de Witt, associate professor of planetary sciences at MIT, MIT said in a statement. “How cool is that?”