Webb Captures Rapid Atmospheric Heating on Eccentric Giant Exoplanet HD 80606 b

NASA says the James Webb Space Telescope has tracked an exoplanet through its closest pass to its star and recorded a rapid burst of atmospheric heating, offering an unusually direct look at how a giant planet responds to a sudden surge of stellar energy.

The findings are preliminary and were presented Tuesday at the 248th meeting of the American Astronomical Society in Pasadena, California, alongside a NASA Webb mission update published June 16 under the headline, “NASA’s Webb Catches Exoplanet Getting Roasted.”

The target was HD 80606 b, a gas giant orbiting a Sun-like star. Using Webb’s Mid-Infrared Instrument, or MIRI, researchers observed the planet before, during and after periastron — the point in its orbit when it swings closest to its star. During the same observing sequence, the planet also passed behind the star from Webb’s point of view, an event known as a secondary eclipse.

That combination matters because HD 80606 b is already one of the most dramatic known laboratories for studying planetary atmospheres. Its orbit is highly elongated, so the amount of starlight it receives changes sharply over a short span of time. NASA says Webb’s data captured the atmosphere reacting in near real time.

“Hot Jupiters are already considered some of the most extreme exoplanets we know of, but even among that population, HD 80606 b is one of the most extreme,” said Tiffany Kataria, the study’s principal investigator at NASA’s Jet Propulsion Laboratory in Southern California.

HD 80606 b has about 4.38 times Jupiter’s mass, takes about 111.4 days to orbit its star and has an orbital eccentricity of about 0.93, making its path far more stretched out than that of the planets in our solar system. NASA says Webb showed the planet’s temperature “skyrockets by 1,100 degrees Fahrenheit” as it plunges toward its star.

Kataria said the heating appeared stronger than expected from earlier infrared observations by NASA’s Spitzer Space Telescope, which had previously monitored the planet during periastron and helped establish it as a key exoplanet target.

“Webb has shown that the planet’s increase in temperature was even more extreme than we anticipated based on Spitzer data,” Kataria said.

What Webb adds is spectroscopy, a technique that splits light into its component wavelengths and can be used to infer both temperature and atmospheric chemistry. NASA says the new MIRI observations are allowing researchers to distinguish specific chemical signatures, including methane and carbon dioxide.

“Spitzer did amazing work on this exoplanet, and now Webb is building on that legacy by enabling us to drill down to distinguish specific chemical signatures like methane and carbon dioxide, which is just amazing progress,” said Ryan Challener, a co-author and research associate at the Cornell Center for Astrophysics and Planetary Science.

NASA identified Laura C. Mayorga of the Johns Hopkins Applied Physics Laboratory as a co-investigator on the work.

The new conference presentation builds on a growing body of Webb observations of the same planet. A separate peer-reviewed JWST NIRSpec study published in 2025 found that HD 80606 b’s emission spectrum changed through periastron and reported detections of methane, water and carbon monoxide after periapse.

Still, the new results remain an early look. NASA’s release describes them as preliminary findings tied to a conference presentation, not a full peer-reviewed paper, and it does not include detailed retrievals or full uncertainty ranges. Even so, the update offers a glimpse of what Webb’s time-resolved mid-infrared studies can reveal about how exoplanet atmospheres change under extreme conditions.