Directly imaging exoplanet air

Astronomers can now do more than spot some exoplanets indirectly: with a coronagraph acting like an artificial eclipse, they are directly imaging a few worlds and splitting their light into atmospheric fingerprints. (webbtelescope.org) A coronagraph blocks most of a star’s glare so a much fainter planet can appear next to it, the same basic problem as trying to see a firefly beside a floodlight. NASA said that is how the James Webb Space Telescope directly imaged planets in the HR 8799 system, about 130 light-years away, and measured carbon dioxide in their atmospheres. (science.nasa.gov) Those measurements come from spectra, which spread a planet’s light by wavelength the way a prism spreads sunlight into colors. Different gases absorb different wavelengths, and Webb teams have reported signatures tied to molecules including carbon dioxide in HR 8799 and water, methane, and carbon monoxide in the free-floating object VHS 1256 b. (science.nasa.gov, webbtelescope.org) The change is that direct imaging is moving from pictures to chemistry. NASA said the HR 8799 observations were the first time carbon dioxide had been directly imaged on planets outside the Solar System, and the result helps test how giant planets formed. (webbtelescope.org) Direct imaging still works for only a small slice of exoplanets: mostly young, hot, giant planets far from their stars, because they glow more brightly and sit farther from the stellar glare. The European Space Agency said only a few tens of exoplanets had been directly imaged before Webb observed the cold giant Epsilon Indi Ab with its Mid-Infrared Instrument coronagraph. (esa.int) That Epsilon Indi Ab result pushed the method toward older and colder planets. The European Space Agency said the planet lies about 12 light-years away and that its colors point to methane, carbon monoxide, carbon dioxide, and possibly thick clouds in the atmosphere. (esa.int) Once astronomers have spectra, they can estimate temperature, cloudiness, and vertical mixing by matching the data to atmospheric models. A 2025 arXiv study of the cold planet WD 0806-661 b reported that a Webb spectrum was consistent with water, ammonia, and methane and used retrieval modeling to infer the planet’s pressure-temperature structure and chemistry. (arxiv.org) Other techniques still dominate the search for smaller and milder worlds. NASA’s Webb exoplanet overview says many of its atmospheric detections so far, including methane and carbon dioxide on K2-18 b and methane plus water vapor on WASP-80 b, came from transit and eclipse measurements rather than direct images. (science.nasa.gov, science.nasa.gov, science.nasa.gov) Researchers are already framing the next step as a search for more detailed atmospheric clues, not just detections of planets themselves. Reviews published in 2025 describe high-resolution spectroscopy as a way to measure molecules, temperature structure, and winds in exoplanet atmospheres, while other studies have proposed carbon dioxide patterns as one possible marker to investigate on temperate rocky planets. (nature.com, nature.com) For now, the directly imaged worlds are mostly giant planets, but the method has crossed from silhouettes into weather-and-chemistry work. The star is still brighter than the planet by orders of magnitude; astronomers are now getting useful air samples anyway. (webbtelescope.org, esa.int)