JWST REVEALS BARE AND AIRLESS WORLD
THE TRAPPIST-1 system, located some 40 light-years away, hosts at least seven Earth-sized, rocky exoplanets. But new measurements taken by the James Webb Space Telescope’s (JWST) Mid-Infrared Instrument (MIRI) show at least one planet — TRAPPIST-1 b — is likely too hot to host an atmosphere.
Despite the news that this planet is inhospitable, the observations are still a major achievement: It is the first time emissions of light have been detected from a rocky planet with a temperature comparable to those in our solar system.
“It’s a really important step in the story of discovering exoplanets,” study co-author Pierre-Olivier Lagage of the French Alternative Energies and Atomic Energy Commission (CEA), who spent more than two decades developing MIRI, said in a press release.
The new research was published March 27 in Nature.
TRAPPIST-1 b, some 1.4 times as massive as Earth, is the innermost world in the system. Previous observations with the Hubble Space Telescope and the Spitzer Space Telescope had found no evidence of a puffy atmosphere around the world. But these observations couldn’t rule out the possibility that the planet was cloaked in a dense, thin atmosphere.
Using JWST, scientists gleaned new insight into TRAPPIST-1 b by measuring its temperature. “This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Lagage. “If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”
JWST watched the planet pass behind its host star, a technique called secondary eclipse photometry. By subtracting the brightness of the red dwarf alone from the overall brightness of the star and planet combined, the team could determine how much infrared light (or heat) the planet emits. That’s no small feat, considering the star is some 1,000 times brighter than the planet, resulting in a dip of less than 0.1 percent when the planet disappears.
They found TRAPPIST-1 b has a temperature around 450 degrees Fahrenheit (232 degrees Celsius). “The results are almost perfectly consistent” with a bare, rocky planet with no atmosphere, said co-author Elsa Ducrot of the CEA.
Studying the TRAPPIST-1 system has wider implications: The host star is an M dwarf, the most common type of star in the galaxy. While finding planets in the habitable zones of such small stars is relatively easy, intense stellar activity may render their surfaces unsuitable for life. “If we want to understand habitability around M stars, the TRAPPIST-1 system is a great laboratory,” Ducrot added. “These are the best targets we have for looking at the atmospheres of rocky planets.”