TRAPPIST-1b is a superhot rocky world just 40 light-years away. Astronomers recently trained the Webb Space Telescope this exoplanet, a world in the TRAPPIST-1 star system, and found that it’s devoid of an atmosphere.
The finding could alter what we know about the formation of exoplanets that orbit similar ultracool red dwarf stars, also known as M stars. Because life as we know it needs an atmosphere to survive, the research also has implications for the search for life beyond Earth. The team’s findings are published today in Nature.
TRAPPIST-1b is the closest planet to the system’s host star, a red dwarf about 9% the mass of the Sun. The world is one of seven, most of which are similar in size to the rocky worlds in our own solar system. Scientists believe TRAPPIST-1b is tidally locked, meaning that one side is always facing the star (called the day side) and one side is always facing away.
The team studied TRAPPIST-1b using observations taken by the Webb Space Telescope between November 8 and December 3, 2022. The Webb telescope launched in December 2021 and began releasing scientific observations last July; since then, it has imaged some of the most famous sights in the galaxy as well as some of the earliest detectable light.
One of Webb’s primary science goals is interrogating exoplanets, or worlds beyond our solar system. In doing so, Webb builds on the work of observatories like the Kepler Space Telescope and TESS, the Transiting Exoplanet Survey Satellite.
Trained on TRAPPIST-1b, Webb found the planet was very hot: Its dayside temperature is roughly 230 degrees Celsius, more than double the boiling point of water. If the planet had an atmosphere, the heat on its dayside would be circulated throughout the planet; instead, the planet is very hot on one side and cold on the other.
“The planet receives less radiation than Mercury in our solar system but somewhere in between Mercury and Venus,” said Taylor Bell, a planetary scientist at NASA Ames Research Centre and a co-author of the study, in a phone call with Gizmodo. “It receives quite a lot of heat. The temperature that we measured is consistent with basically just a rock just being baked by the sunlight.”
TRAPPIST-1b has been studied before by the Hubble and Spitzer space telescopes; though both observatories found a puffy atmosphere did not exist, they were not able to rule out the possibility of a denser one, according to a European Space Agency release.
Using its Mid-Infrared Instrument (MIRI), Webb was able to eliminate the possibility of an atmosphere altogether. TRAPPIST-1b is 100 times closer to its host star than Earth is to the Sun; because its host star is active, it can wipe out any atmosphere a planet generates. (In the distant past, Earth developed a secondary atmosphere after losing its first one.)
TRAPPIST-1b “is close to the star and it gets 4x the amount of stellar energy flux that Earth gets from the Sun,” said Tom Greene, a planetary scientist at NASA Ames Research Centre and the study’s lead author, in an email to Gizmodo. “It would be interesting to see if the next closest planet, TRAPPIST-1c, has an atmosphere, because that one gets about as much stellar heating as Venus gets, and Venus has a thick atmosphere.”
“No thick atmosphere on planet c could mean that it is difficult for M star planets to have atmospheres,” Greene added.
At just 40 light-years away and with a septet of worlds to scrutinize, the TRAPPIST-1 system will no doubt be a recurring target of Webb’s infrared observations. It is a perfect place for planetary scientists to explore theories about exoplanets and red dwarf systems.