JWST Discovers Its First Exoplanet

The JWST used a transit light curve to detect exoplanets. The NIRSpec shows the changes in brightness as the exoplanet crosses in front of the star. By calculating the brightness difference and how low the light was dimmed, the planet’s size and orbit can be determined. Credit: NASA, ESA, CSA, L. Hustak (STScI).

JWST was launched into space on December 25, 2021, and started taking pictures and collecting data a few months later. Since the telescope has been fully operational, JWST has been observing the dark depths of our universe. On January 11, 2023, Kevin Stevenson and Jacob Lustig-Yaeger, both from the Johns Hopkins University Applied Physics Laboratory, announced that their team had discovered JWST’s first exoplanet.         

The exoplanet LHS 475 b is 41 light-years away from us in the constellation Octans. This constellation was suggested as an area of interest based on results from NASA’s Transiting Exoplanet Survey Satellite, a satellite whose main objective is to detect exoplanets around dwarf stars. JWST detected the exoplanet using its Near InfraRed Spectrograph (NIRSpec). The exoplanet is a rocky planet with a diameter of 99% of Earth’s diameter. LHS 475 b has a short orbital period around its red dwarf star — only two days — and is closer to the star than Mercury is to our Sun. This star, however, is cooler than our Sun, which means that there is some chance that LHS 475 b could have an atmosphere.

JWST is the only operating telescope that is capable of characterizing atmospheres on Earth-sized planets. While the transmission spectrum from LHS 475 b has not yet been fully analyzed, Stevenson and Lustig-Yaeger’s team has been able to start ruling out some compositions for its possible atmosphere. For example, they can be certain that it does not have a thick, methane-rich atmosphere similar to Saturn’s moon Titan. The planet is also a few hundred degrees warmer than Earth. This means that if clouds are detected, the planet may be more like Venus, with a carbon dioxide atmosphere. However, a 100% carbon dioxide atmosphere is very compact and more challenging to detect. In order to determine the difference between a pure carbon dioxide atmosphere and no atmosphere at all, more data will need to be collected. READ MORE