Time to sniff some alien air! A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured by the James Webb Space Telescope’s Near-Infrared Spectrograph on July 10, 2022, reveals the first clear evidence for carbon dioxide in a planet outside the solar system. Each of the 95 data points on this graph represents the amount of a specific wavelength of light that is blocked by the planet and absorbed by its atmosphere. Wavelengths that are preferentially absorbed by the atmosphere appear as peaks in the transmission spectrum. The peak centered around 4.3 microns represents the light absorbed by carbon dioxide. WASP-39 b orbits a Sun-like star roughly 700 light-years away, in the constellation Virgo. The planet orbits extremely close to its star (less than 1/20th the distance between Earth and the Sun) and completes one orbit in just over four Earth-days. The planet’s discovery, based on ground-based observations, was announced in 2011. The star, WASP-39, is roughly the same size, mass, temperature, and color as the Sun. The background illustration of WASP-39 b and its star is based on current understanding of the planet from Webb spectroscopy and previous ground- and space-based observations. Webb has not captured a direct image of the planet or its atmosphere. #WebbDiscovery #exoplanet #NASAWebb #JWST #WebbScience Credit: NASA, ESA, CSA, and Leah Hustak (STScI). ALT-TEXT: Graphic titled “Hot Gas Giant Exoplanet WASP-39 b Atmosphere Composition, NIRSpec Bright Object Time-Series Spectroscopy.” The graphic shows the transmission spectrum of the hot gas giant exoplanet WASP-39 b captured using Webb’s NIRSpec Bright Object Time-Series Spectroscopy mode, with an illustration of the planet and its star in the background. The data points are plotted as white circles with grey error bars on a graph of amount of light blocked in percent on the vertical y axis versus wavelength of light in microns on the horizontal x-axis. One broad, prominent peak visible in the data and model is labeled “Carbon Dioxide, C O 2” The carbon dioxide peak is centered around 4.3 microns and has a y value of between 2.25 and 2.30 percent of light blocked.