3I/ATLAS Update: 'Mysterious Intruder' Comet Is Now 'Very Bright And Active'

It's the most high-profile galactic interloper to cross our cosmic boundary in years, and now, the celebrity comet 3I/ATLAS is putting on a dramatic show before it disappears into the void forever. Dubbed an 'intruder from parts unknown', this massive, jet-spewing snowball is giving Earth's space agencies a final, spectacular set of images as it makes its way out of our solar system for good.

Discovered in late June and officially confirmed as the third known interstellar object in July — following its famous predecessors, 1I/'Oumuamua and 2I/Borisov — 3I/ATLAS has been an astronomical sensation. The comet was initially spotted by the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile.

Over the past several months, it has been zooming through the inner solar system at an estimated breathtaking speed of 130,000 mph (210,000 km/h). It has been approaching our system from the general direction of the constellation Sagittarius. The colossal object had its closest encounters with Mars and the sun in October.

Specifically, it made its closest approach to the sun on Oct. 30, 2025, at a distance of about 130 million miles (210 million km), just outside the orbit of Mars. It is now set for its final, crucial astronomical milestone: a close encounter with Earth on Dec. 19. While we won't be queuing for tickets — the comet will still be a colossal 170 million miles (270 million kilometers) away, or nearly twice the distance between our planet and the sun — it is the best viewing window for scientists to snap a last look at a visitor from beyond.

As the comet hurtles toward this final flyby, spacecraft managed by NASA and the European Space Agency (ESA) are snagging as many close-up observations as their instruments allow. This week, new images have been shared by both agencies, providing undeniable proof that its recent flyby of the sun has left it very bright and active as it spews large amounts of sublimated gas and dust into space, giving us an unprecedented view of its cosmic inner workings.

Peering Through the Veil: How NASA's Hubble Tracked 3I/ATLAS

On Thursday (Dec. 4), NASA shared the latest dramatic image of 3I/ATLAS taken by the Hubble Space Telescope. The photograph, which requires an intense photographic technique to capture, shows the comet as a glowing white dot at the centre, representing the comet's nucleus (its main body) and the surrounding coma.

The coma is the bright atmosphere of gas and dust that wraps around the comet before ultimately being funnelled into its tail, creating the spectacular visible effect. For the picture, Hubble's camera had to stay fixed on the fast-moving comet, resulting in the background stars being stretched into long, ethereal streaks — a stunning reminder of the sheer velocity of this visitor.

Comets naturally brighten as they approach the sun, a phenomenon that occurs when the ice trapped within their structure heats up and sublimates, essentially turning straight from a solid into a gas. This resulting solar radiation then pushes this gas into a tail that always stretches away from the sun.

Furthermore, the warmest, sun-facing side of the comet may erupt with jets of gas and dust angled toward our star. Both of these dramatic features are faintly visible in the new Hubble image, giving scientists critical data on the body's composition.

NASA managed to snap this particular image on Nov. 30, when Hubble was about 178 million miles (286 million km) from the comet. This distance is significantly closer than when Hubble first imaged the comet in late July.

Although that first, fleeting view showed little more than a blue blur, it was enough to allow scientists to constrain the size of 3I/ATLAS to somewhere between 1,400 feet (440 meters) and 3.5 miles (5.6 km) wide. This places it as likely the largest interstellar object seen to date, dwarfing its predecessors. Full data on the coma's chemical composition is expected soon.

Unexpected Payoffs: The Juice Mission Captures 3I/ATLAS

Also on Thursday, the ESA shared its latest view of the comet, but this one came from a truly unexpected source: the Jupiter Icy Moons Explorer (Juice) orbiter. The spacecraft, which is currently en route to study Jupiter's moons for signs of life, took the image on Nov. 2, just days after 3I/ATLAS's incredibly close approach to the sun.

Located even closer to its target than Hubble — at only 41 million miles, or 66 million km, away — the Juice image shows a comet absolutely brimming with activity. An ESA spokesperson confirmed the dramatic detail, writing, 'Not only do we clearly see the glowing halo of gas surrounding the comet known as its coma, we also see a hint of two tails. The comet's 'plasma tail' — made up of electrically charged gas, stretches out towards the top of the frame. We may also be able to see a fainter 'dust tail' — made up of tiny solid particles — stretching to the lower left of the frame'.

While this is a thrilling teaser, we won't fully understand what Juice's five scientific instruments saw until much later. The full data set won't reach Earth until late February 2026, as the orbiter is currently using its main antenna as a heat shield during its pass of the sun, forcing it to rely on a slower, less efficient antenna to beam its observations back.

This collection of spectacular images is a powerful reminder that human space exploration continually delivers unexpected payoffs. Hubble and Juice are just two of a dozen spacecraft that have observed 3I/ATLAS from around the solar system, including Mars rovers, solar orbiters, asteroid trackers and space telescopes that were never specifically intended to track comets.

When you're dealing with a mysterious intruder from parts unknown, every observation matters. And there is still more to come: as 3I/ATLAS draws closer to Earth, the James Webb Space Telescope will take another critical look at it, while countless scientific observatories and amateur astronomers across the globe will also have their chance to watch its final moments in our celestial neighbourhood.