JWST Watches Exoplanet HD 80606 b Heat Up by 1,100°F in Hours During Periastron
Summary: On June 18, 2026, NASA's Webb MIRI instrument revealed the 4-Jupiter-mass hot Jupiter HD 80606 b heats up by ~1,100°F in hours at periastron, with its atmospheric chemistry reshaping in real time each 111-day orbit.
NASA's James Webb Space Telescope has delivered the most detailed real-time observation of a hot Jupiter heating up ever recorded. HD 80606 b, a gas giant roughly four times the mass of Jupiter located about 215 light-years away in the constellation Ursa Major, orbits a Sun-like star on a highly eccentric 111-day path. Unlike the nearly circular orbits of planets in our solar system, HD 80606 b swings far from its star at apoapsis, then plunges close at periastron—causing the stellar radiation it receives to change dramatically within hours.
Using Webb's Mid-Infrared Instrument (MIRI), the research team continuously monitored the planet's atmosphere before, during, and after its closest approach. The data show that HD 80606 b's upper atmospheric temperature surged from roughly 525°C to about 1,250°C in under 20 hours—a swing exceeding 600°C (approximately 1,100°F), the largest real-time temperature range ever measured on a planetary atmosphere. At the moment of periastron, the planet also passed behind its host star from Webb's line of sight, producing a secondary eclipse that gave the team an additional calibration point for the planet's thermal emission.
Perhaps most striking is the dynamic shift in atmospheric chemistry. Webb's spectral data reveal that as temperatures swing wildly over each 111-day orbit, the molecular composition of HD 80606 b's upper atmosphere reshapes in real time—certain molecules dissociate at peak heat and recombine as the planet cools. This finding demonstrates that hot Jupiter atmospheres are not static chemical environments but dynamic systems that continuously respond to orbital forcing. The results provide an unprecedented observational benchmark for understanding planetary atmospheric physics under extreme conditions.