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Jupiter’s Atmosphere Holds Steady

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A close-up photograph of Jupiter. Dramatic cloud bands encircle the planet, and a large dark shadow of a nearby moon appears at left.
An image of Jupiter taken by the Juno spacecraft, with the shadow of the moon Ganymede visible on the cloud tops. [Image data: NASA/JPL-Caltech/SwRI/MSSS, Image processing by Thomas Thomopoulos]

Jupiter’s upper atmosphere is hundreds of degrees hotter than it has any right to be, and for decades astronomers could only study it in brief, seemingly chaotic glimpses. New global maps built from years of observations have finally revealed the big picture — and it is surprisingly calm.

Order from Chaos

Although we’re well acquainted with Jupiter, having sent eight spacecraft on close passages and lived with it dominating the night sky for millennia, some of its simplest characteristics continue to puzzle us. For example, high above Jupiter’s cloud bands, temperatures exceed 800 K — far hotter than we’d expect given the meager sunlight that reaches that distance. Astronomers have long suspected that this excess is deposited by energy from the planet’s brilliant polar auroras, but previous observations provided only localized, sporadic snapshots that collectively painted a confusing picture of an ever-changing landscape.

A photograph of Jupiter seen in red/orange false color with a dark stripe down the middle.

Jupiter as seen by the slit camera on the Keck telescope during one of the team’s observations. The spectrograph slit is the dark vertical band stretching from the equator to the north pole, and the Great Red Spot appears in black at the lower right. [Adapted from Roberts et al. 2026]

To truly understand how Jupiter’s upper atmosphere got so hot and whether it was actually changing over time, astronomers needed to construct a global, comprehensive map — and then do so repeatedly over several years and look for any changes. A team led by Kate Roberts (Boston University) has now assembled just this sequence using the NIRSPEC instrument at the Keck Observatory. The researchers collected over 175,000 high-resolution infrared spectra across 14 nights from 2022 to 2025; they then processed the massive dataset to extract the emission from a charged form of hydrogen, H3+. This species is a standard natural thermometer that glows at infrared wavelengths, and by mapping the spectra to their corresponding specific locations on Jupiter, the team could construct the first true global maps of Jupiter’s upper atmospheric temperature, density, and radiance.

Consistency is Key

A look at how the maps evolved over time revealed striking order: the spatial patterns remained nearly constant, and the temperatures barely changed even over years. In general, the team noted that temperature decreases smoothly from the auroral regions near the poles (~1,150 K) to the equator (~750 K) at every longitude, and that although there is some night-to-night temperature variation, things stay remarkably steady over the years-long baseline.

A 2D heatmap with longitude on the bottom axis and latitude on the vertical axis. There is a general trend towards higher temperatures at higher latitudes.

A map of the average temperature of Jupiter’s upper atmosphere, as measured by the new Keck NIRSPEC data. Click to enlarge. [Adapted from Roberts et al. 2026]

What once “appeared stochastic,” the authors write, “exhibits predominantly spatial rather than temporal variability.” Earlier observations were simply sampling different longitudes at different times, mistaking geography for weather.

The conclusion that the upper atmosphere is complex but steady has implications beyond just Jupiter, as the team notes that JWST has already observed spatial patterns in the temperatures of the upper atmospheres of both Uranus and Neptune. As Roberts and colleagues note, “similar physical mechanisms could give rise to comparably stable structures” on those distant ice giants, meaning this analysis could ground our understanding of the upper atmospheres of giant worlds across the solar system.

Citation

“A Global View of Jupiter’s Upper Atmosphere Through H3+,” Kate Roberts et al 2026 ApJL 998 L13. doi:10.3847/2041-8213/ae3c9b