Astronomers have discovered an Earth-sized planet bombarded with so much radiation that its atmosphere long ago eroded, leaving it exposed. Life as we know it cannot exist on this sweltering world, but astronomers are interested for another reason: They may be able to study life for the first time geology a planet outside our solar system.
The new found exoplanetCalled SPECULOOS-3 b, it is a rocky planet about 55 light-years from Earth. It orbits its parent star every 17 hours, but the planet’s days and nights are endless. Astronomers suspect that the planet is tidally locked to its star, just as the moon is locked to Earth. A single day side always faces the star, while the night side is locked in eternal darkness.
Telescopic observations show that the exoplanet’s star, a 7-billion-year-old red dwarf in size, often emits radiation Jupiter, heating the planet to Venus-like temperatures. So any atmosphere on the planet could have easily escaped into space long ago, leaving behind an airless, sizzling ball of rock, astronomers reported in the new study, published May 15 in the journal Natural astronomy.
“Life as we know it could not arise on the surface of the planet – atmosphere or not – because it could not absorb large amounts of water in liquid form,” said the study’s lead author Michael Gillon, an astronomer at the University of Liège in Belgium, told Live Science. “It’s like a bare rocky planet mercury.”
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Although SPECULOOS-3 b is not life-friendly, astronomers said it is close enough to Earth to conduct detailed follow-up studies of its chemical composition, which would reveal whether the planet was ever geologically active. Already planned observations with the James Webb Space Telescope (JWST), for example, will be able to confirm whether volcanoes have erupted on the planet. This would reveal how rocky planets like SPECULOOS-3 b form around faint, light stars and whether some of them could be conducive to life despite their proximity to their stars.
The researchers searched “intensively” for SPECULOOS-3 b’s planetary siblings in the same star system, but found none, Gillon said. He determined that these additional planets may exist, but are simply too small or too far from their parent star to be seen.
A hot planet around a cool star
Gillon and his colleagues discovered SPECULOOS-3 b since 2011 using a network of six telescopes spread across Chile, the Canary Islands and Mexico. This network is called Search for Planets Eclipsing Ultra-Cool Stars, or SPECULOOS, which shares its name with a Belgian spiced shortbread traditionally given to children every December 6th for St. Nicholas Day.
The project’s main goal is to discover rocky planets orbiting ultracool dwarf stars, whose small size makes it easier for telescopes to detect orbiting planets. Not only are they thousands of degrees cooler than the sun and hundreds of times weaker, but they also burn their fuel slowly and end up living much longer – around 100 billion years. (The sun will be around 10 billion years old when it dies in about 4.5 billion years.)
“They are expected to be the last shining stars in the universe,” said the study’s co-author Amaury Triauda professor of exoplanetology at the University of Birmingham in England said in a opinion. Their particularly long lifespans provide favorable time windows for the emergence of life on planets within their systems, the researchers say.
However, their extreme weakness makes them difficult to study. To discover SPECULOOS-3 b, a SPECULOOS robotic telescope in Mexico continuously observed telltale dips in the host star’s light for five nights in 2021. At that time, the first evidence of the newly discovered planet orbiting appeared and was confirmed a year later, according to the study.
“If there were no atmosphere, there would be no blue sky and no clouds – it would just be dark, like on the surface the moon,” co-author of the study Benjamin Rackhamsaid a researcher at MIT in a separate paper Statement from MIT. “And the ‘Sun’ would be a large, purple, spotted and brilliant star that would look about 18 times larger than what the Sun looks to us in the sky.”
SPECULOOS-3 b is the ninth such planet discovered by the project, and the team expects to discover many more in the coming years, Gillon said. Like the planets previously discovered by the project – including a family of seven in the known TRAPPIST-1 system, some of which are considered potentially habitable – the newly discovered SPECULOOS-3 b “is an excellent target for JWST,” Gillon said.
“With this world, we could basically start exoplanetary geology,” said study co-author Julien de Wit, an assistant professor of planetary science at MIT, said in the MIT statement. “How cool is that?”