Cold Footprints on Jupiter, and a Comet Heading for the Sun

Jupiter’s aurora never switches off. Earth’s northern lights flicker and fade, but Jupiter’s glow constantly, hundreds of times brighter, fed by the most powerful magnetic field of any planet. And unlike Earth’s aurora, Jupiter’s has a strange feature: footprints.

Each of Jupiter’s large moons leaves a glowing mark on the aurora, a bright spot where the moon’s connection to the planet’s magnetic field meets the atmosphere. The innermost moon, Io, leaves the brightest one. Io is the most volcanically active world we know of. Its eruptions hurl charged material into space, and that material eventually rains down onto Jupiter, lighting up a spot that tracks Io’s orbit like a shadow.

Scientists have known about these footprints for years. But until now, they’d only measured how bright they were, never what was physically happening inside them.

On 3 March, a team led by Katie Knowles at Northumbria University published the first spectral measurements of the footprints, using data from the James Webb Space Telescope. JWST captured a series of snapshots of Jupiter’s northern aurora in September 2023. Most looked normal. In one, something unexpected appeared: a cold spot, sitting directly inside Io’s footprint. The surrounding aurora was blisteringly hot. This patch was roughly half that temperature. At the same time, the density of charged particles in that area was several times higher than anywhere else.

Here’s the part that stops me: the change happened in minutes. Not over days or weeks. Whatever Io’s volcanic output was doing to Jupiter’s magnetic environment, it was doing it fast, and in ways nobody had predicted.

Saturn’s moon Enceladus also sprays material into space and also leaves a footprint on Saturn’s aurora. If the same cold-spot phenomenon happens there, it would mean this isn’t a quirk of Jupiter but something fundamental about how giant planets and their moons interact. Knowles has been awarded telescope time in Hawaii to look into exactly that.

A comet with a 2,400-year family tree

In 371 BC, Aristotle observed a comet bright enough to cast shadows. That comet eventually broke apart, and its fragments have been drifting through the solar system ever since, each one following a similar orbit, each eventually making its own close pass of the Sun. The Great Comet of 1843 was one fragment. Comet Ikeya-Seki in 1965, which became visible in broad daylight, was another. Astronomers call them the Kreutz sungrazers.

The latest member of this ancient family was spotted on 13 January by four French amateur astronomers (Maury, Attard, Parrott and Signoret, giving the comet its name: MAPS) from a small observatory in Chile’s Atacama Desert. On 4 April, it will skim just 159,000 kilometres above the Sun’s surface. For context, the Moon is 384,000 kilometres from Earth. This comet will pass closer to the Sun than the Moon is to us, travelling at over 3 million kilometres per hour.

The question: will it survive? Sungrazers often don’t. The heat is brutal and the Sun’s gravity can tear a fragile nucleus apart. But MAPS was discovered unusually early and appears to be actively outgassing, which suggests a reasonably large nucleus. Its brightness curve looks similar to some of the more successful Kreutz comets. If it holds together through perihelion on 4 April, it could brighten rapidly and become visible to the naked eye in the evenings shortly after, possibly with a long, ghostly tail stretching away from the Sun.

That’s a big “if.” But it’s a genuinely exciting one.

Talking about this with your kids

Jupiter is one of the brightest objects in the sky right now. Go outside on a clear evening and find it. Then tell your child that right now, volcanoes on one of its moons are firing material into the planet’s atmosphere and leaving glowing footprints on its northern lights. A telescope orbiting a million miles from Earth just measured the temperature inside one of those footprints. It was colder than it should have been, and nobody knows exactly why yet.

Then mark 4 April on the calendar. If Comet MAPS survives its encounter with the Sun, there may be something to look for after sunset, low on the western horizon: a faint tail stretching upward, the remains of a comet that might trace its family tree back to something Aristotle saw. No telescope needed. Just a clear view of the horizon and some patience.

Not every comet survives. Not every mystery gets solved quickly. But both of these stories are unfolding right now, above our heads. That’s worth stepping outside for.

Sources and further reading

Knowles et al., Geophysical Research Letters, 3 March 2026: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025GL118553

Northumbria University press release: https://www.northumbria.ac.uk/about-us/news-events/news/telescope-reveals-surprising-secrets-in-jupiters-northern-lights/

Space.com coverage: https://www.space.com/astronomy/jupiter/jupiters-moons-leave-cold-footprints-in-the-planets-auroras-james-webb-space-telescope-finds

Sky & Telescope on Comet MAPS: https://skyandtelescope.org/astronomy-news/new-kreutz-comet-c-2026-a1-may-dazzle/

EarthSky guide to Comet MAPS: https://earthsky.org/space/new-sungrazing-comet-c-2026-a1-comet-maps/

Wikipedia on C/2026 A1 (MAPS): https://en.wikipedia.org/wiki/C/2026_A1_(MAPS)