James Webb Space Telescope Heralds New Era in Exoplanet Studies

Transmission spectrum of the atmosphere of WASP-96b. The labeled peaks denote the presence of water vapor, though the relatively low height of the peaks suggests clouds, which suppress water features. The downward slope of the measurements at shorter wavelengths could indicate hazes in the atmosphere. Credit: NASA/ESA/CSA/STScI.

NASA’s James Webb Space Telescope (JWST) was launched in 2021 and recently completed its deployment and mirror alignment. The start of the primary science phase of the mission was heralded on July 12, 2022, with the release of five new images. One observation led to the identification of water and the detection of evidence for clouds and hazes in the atmosphere of WASP-96b, a hot gas giant planet approximately 1,150 light-years away that closely orbits its parent star at one-ninth the distance between the Sun and Mercury.

To make this identification, JWST’s Near Infrared Imager and Slitless Spectrograph (NRISS) observed the WASP-96 system over a 6.4-hour period as the exoplanet transited across its star, measuring light in the 0.6 to 2.9-micron range. A transmission spectrum that shows how much of the star’s light is blocked at certain wavelengths was calculated from these measurements by comparing light that filtered through the atmosphere of the exoplanet to unfiltered light. Since different gases preferentially absorb light at different wavelengths, the spectrum provides information about the presence and abundance of various gases in the atmosphere of the exoplanet.

JWST is not the first space telescope to analyze the atmospheres of exoplanets, but its advanced design yields a dramatic improvement in spectral resolution and sensitivity, as does its location in solar orbit at a Sun-Earth gravitational equilibrium site (Lagrange Point 2), far from the influence of Earth’s atmosphere. Moreover, JWST observes at wavelengths longer than 1.6 microns, a portion of the spectrum inaccessible to other telescopes. These wavelengths are sensitive to water, as was detected at WASP-96b, but also gases like oxygen, methane, and carbon dioxide, which are relevant to astrobiology. Nearly a quarter of JWST’s first observation cycle is dedicated to the spectroscopy of dozens of exoplanets of all kinds. The data to be returned have the potential to revolutionize our understanding of planets in the cosmos. READ MORE