The James Webb Space Telescope has achieved one of its first major science goals announced back in 2017. Infrared instruments have now detected the atmosphere surrounding one of the TRAPPIST-1 exoplanets.
James Webb succeeded the aging Hubble Telescope, whose massive mirror collects more light than any previous telescope to produce high-resolution images, while its infrared sensing allows it to peer deeper into space and time. Overall, JWST has proven invaluable in providing new insights into the early history of stars, planets, and the universe itself.
In 2017, astronomers discovered an extraordinary system of seven Earth-sized exoplanets orbiting a nearby red dwarf star called TRAPPIST-1, just 40 light-years away. Naturally, scientists began to wonder what these fascinating exoplanets would look like through the eyes of the yet-to-be-launched JWST. The system soon became one of the telescope's first official science targets, with the goal of studying the potential habitability of these planets.
Now, using a method called transmission spectroscopy, it has provided the first glimpse of TRAPPIST-1b's innermost world. As a planet passes in front of its host star, light passes through any atmosphere that may be present, blocking different wavelengths of light to varying degrees depending on the molecules in the air. By analyzing the spectra, astronomers can determine the composition of the atmosphere and derive other information from it, such as whether the planet is habitable.
The team found no signs of atmospheric activity in TRAPPIST-1b - the detected spectra could be attributed entirely to stellar activity. This finding is consistent with other Webb observations made earlier this year that measured the planet's temperature and found that an atmosphere was unlikely. However, the possibility that it has a thin atmosphere composed of pure water, carbon dioxide or methane cannot be ruled out.
"Our observations found no evidence of an atmosphere surrounding TRAPPIST-1b," said study author Ryan MacDonald. "That tells us that the planet could be a bare rock with clouds high up in the atmosphere, or it could have very heavy molecules like carbon dioxide that make the atmosphere too small to detect. But what we're seeing is that the star is definitely the biggest influence dominating our observations, and that will have the exact same effect on the other planets in the system."
TRAPPIST-1b is primarily a technical test of its more interesting neighbors - TRAPPIST-1d, e and f - which all orbit within the star's habitable zone. Researchers say the study helps them understand how to account for stars' hot spots, flares and other activity that can affect atmospheric readings.
The research was published in The Astrophysical Journal Letters.