The James Webb Space Telescope has been making itself useful lately. In its latest look, the James Webb Space Telescope revealed an eerie “blue glow” shimmering in the middle latitudes of Neptune, and it revived the long-running hunt for auroras on both ice giants. Auroras are a planet’s neon sign: charged particles ride invisible magnetic rails and crash into thin air high above the clouds, making the sky light up.
What the “blue” really is
That glow is real, but the color gives us tips about the planet. The James Webb Space T. detects the light from a molecule called H₃⁺ in infrared wavelengths, beyond the colors our eyes see. Scientists map that invisible signal into blues so the pattern pops, like translating a whisper into a readable subtitle. We are simply watching an aurora that sits far from Neptune’s poles—the first clear detection of its kind on that world.
Neptune’s magnetic field is wildly askew—tilted and off-center—so its field lines thread the atmosphere in unexpected places. That helps explain why Webb Space picked up auroras in the mid-latitudes instead of at the planet’s crowns. The detection used instruments that split light into “fingerprints,” letting researchers separate auroral glow from the planet’s normal heat. It’s strong, direct evidence that Neptune’s space weather can crackle far from the poles.
Uranus, the oddball partner
Uranus has sported auroras in past Hubble campaigns, but the telescope adds richer, crisper views of the planet’s rings, storms, and bright polar cap—the stage on which future auroras will be tracked. Uranus’s magnetic field is tipped and offset, so its lights can wander far from the geographic poles too. Recently, long-term Hubble work even fine-tuned Uranus’s day length to 17 hours, 14 minutes, 52 seconds by tracking the motion of auroral features. With these tools, scientists can watch changes night after night and link them to gusts in the solar wind.
Auroras, apart from being pretty and giving us beautiful pictures of planets, are useful to space scientists too. By following H₃⁺ with the JWST, researchers can probe the temperature and chemistry of the upper atmosphere, test models of each planet’s quirky magnetic field, and even time a planet’s internal day more precisely by watching how the auroral engine rotates. That’s crucial as proposals for a flagship Uranus orbiter move forward; every Webb Space snapshot helps mission planners aim for the right seasons and the right questions.
What we learned in the past decade that sets the scene
These worlds —much like or own home planet Earth— are dynamic. Hubble has traced Neptune’s clouds waxing and waning with the Sun’s 11-year cycle, hinting that ultraviolet sunlight kick-starts hazes that grow into clouds—with a lag of roughly two years. That solar-paced rhythm helps explain why some observing seasons look strangely bare and others turn lively.
From Earth, astronomers recently did something once thought impossible: the ESO Very Large Telescope caught a dark spot—a giant storm—prowling Neptune’s atmosphere, plus a bright companion cloud. That ground-based view means we can now watch storms evolve without relying only on fleeting spacecraft flybys.
And the modern portraits of Uranus tell their own tale. JWST resolved the delicate rings and a shining north polar cap in 2023, offering a crisp stage set for tracking auroras against changing seasons. That seasonal context will matter as the planet tips deeper into northern spring, reshaping how its magnetosphere meets the solar wind.
How Webb Space captured the glow—and what’s next
In 2023, observers used NIRSpec to take a spectrum that cleanly flagged the molecule and tied it to auroral activity. Next steps are clear: repeat the observations across seasons, stitch them to Hubble’s cloud record, and keep an eye out for storms that may shuffle the auroral dance. Before long, Webb Space will hand off a playbook to the first probe brave enough to dive into these blue worlds.