The James Webb Space Telescope observations of WASP-39b: the most detailed astronomical data ever on an exoplanet
The James Webb Space Telescope (JWST) has produced the most detailed information ever on an exoplanet, making it the world we know most about after the eight major planets of our Solar System. There are clouds on the planet, and it is possible to detect a chemical reaction in it’s atmosphere.
Laura was part of the observation team and said they have studied lots of planets before. “But we’ve never seen a data set like this.” The team posted five papers1,2,3,4,5 on its findings on the arXiv preprint server on 22 November.
The planet was seen for more than 40 hours by the telescope. Initial results showed carbon dioxide in the planet’s atmosphere. It was the first time that the gas had been seen on an exoplanet.
“Photochemistry, because it is such an important process here on Earth, is probably an important process on other potentially habitable planets,” says Jacob Bean, an astronomer at the University of Chicago in Illinois and the observation team’s co-leader. Until now, we have only been able to test our understanding of photochemistry in the Solar System. But planets around other stars give us access to completely different physical conditions.”
Such inward migration of hot Jupiters is expected, to explain their proximity to their stars. It is not known if this is a slow process, over a long time, or if it is a result of a spaceship from another planet. Knowing WASP-39b’s composition could help astronomers to determine which scenario occurred.
The planet is tidally locked to its star, with the same face always pointing towards it, because of the immense gravitational attraction between them. And the observations show that it has incomplete cloud cover — something that astronomers have never observed before on an exoplanet. At the boundary of night and day, the planet is “only about 60% covered by clouds”, says Bean — perhaps because clouds evaporate as they reach the hotter (day) side and condense as they reach the cooler side.
First results from the Joint Wide-Field Spectrometer (JWST) experiment of TRAPPIST-1b: Implications for the planet’s atmosphere
“We’re in business,” Björn Benneke, an astronomer at the University of Montreal, said during a symposium on first results from JWST in Baltimore, Maryland, on 13 December.
In a poster presentation at the conference, Olivia Lim of the University of Montreal showed two JWST observations of the innermost planet in the system, TRAPPIST-1b. She can’t yet tease out a signal indicating the planet’s atmosphere. It probably doesn’t have a puffy, hydrogen-rich atmosphere like planet 1g.
Benneke showed the first JWST studies of TRAPPIST-1g. So far, the telescope has been able to make out that it probably doesn’t have a hydrogen-rich atmosphere — which would be relatively easy to spot because it is so physically large. That could mean that the planet has a denser atmosphere, made of heavier molecules, such as carbon dioxide, or no atmosphere at all.
“We needed this first look to know what we’re dealing with,” says Knicole Colón, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in the work. Benneke declined to speak with reporters about the TRAPPIST-1g results, citing a paper under review at a scientific journal.
Near-Infrared Spectroscopy of the WASP-39b Exoplanet: Challenges and Problems in Optimising Data Processing
The sulfur/oxygen ratio is another piece in the puzzle of planetary formation. The sulfur content of the atmosphere of an exoplanet is intriguing. The protective ozone in Earth’s atmosphere is similar to sulfur dioxide, produced during chemical reactions triggered by the host star7. Rustamkulov et al. and Alderson et al. The atmosphere of WASP-39b had sulfur dioxide in it. The first direct evidence of light-based reactions in a exoplanet atmosphere marks an important milestone in the search for a truly habitable planet.
The instruments used in the studies are all in the near IR range, which is where one expects to find the key atmospheric molecule reported. But each instrument has different configurations that enable access to different wavelength ranges and spectral resolving powers. Rustamkulov et al. and Ahrer et al.4 used two configurations of an instrument called the Near Infrared Spectrograph; Feinstein et al. used the Near Infrared Imager and Slitless Spectrograph; and Ahrer et al.5 used a device known as the Near Infrared Camera. The teams observed light with differing heights from 1.5 to 5.5 micrometres.
Various data-processing algorithms were used for each instrument to traverse the complex path from raw data to the final spectrum. And although these efforts returned mostly similar results, the diverse approaches show that there is no consensus yet on the optimal way to process JWST data — indeed, there is much still to learn. Some problems have already begun to be addressed in these initial studies, including how best to manage pixels that are saturated1 (giving unreliable signals), and what to do when mirror segments spontaneously tilt during observation2.