The James Webb Space Telescope has measured its first transit light curve and also the composition of the planet's atmosphere. They have now been posted online by NASA as Webb Images. For this first observation of a transiting planet, WASP-96b was chosen, a hot Jupiter that orbits its star in just 3.4 days.
WASP-96b was discovered along with six other planets using ground-based telescopes (WASP-South). The article, published in MNRAS in 2013, states: "Since WASP host stars are generally brighter than host stars of Kepler exoplanets, ongoing WASP-South discoveries are important for detailed study of exoplanets and will be prime targets for future missions such as CHEOPS and JWST..."
The same spectrometer, one of three aboard JWST, was then used to make the measurements in the wavelength range between 0.75µm and 2.75µm that allowed the composition of WASP-96b's atmosphere to be determined. One can clearly see the characteristic lines of water:
These first measurements are of a hot Jupiter orbiting a G8 star. For the future it will be exciting, namely when the atmospheres of Earth-like planets are observed. Proposals for this already exist and for years our department has been working on simulations of planetary atmospheres and model calculations on the detectability of different molecules.
Here are two articles about characterizing and detectability of terrestrial planets:
Atmospheric characterization of terrestrial exoplanets in the mid-infrared: biosignatures, habitability, and diversity von Sascha P. Quanz et al (darunter John Lee Grenfell und Heike Rauer), Experimental Astronomy, 2021
Influence of Biomass Emissions on Habitability, Biosignatures, and Detectability in Earth-like Atmospheres von Stefanie Gebauer, Iva Vilovic, John Lee Grenfell, Fabian Wunderlich, Franz Schreier und Heike Rauer, Astrophysical Journal, 909:128, 2021