In late November 2025, the Hubble Space Telescope turned its gaze back to the cosmic traveller: 3I/ATLAS. At a distance of about 286 million kilometres from Earth, Hubble captured new images revealing a bright core surrounded by a glowing cloud of dust and gas. As the telescope tracked the comet, not the stars, the background stars streaked across the sky while the comet stayed sharp and clear. These fresh observations have re-energized astronomers and skywatchers. They offer a deeper view into how this icy, interstellar object behaves.
A cosmic visitor from beyond
3I/ATLAS is not like most comets we know. It doesn’t orbit the Sun in a regular, repeating path. Instead, it follows a hyperbolic trajectory. That means it came from interstellar space, from another star system, and is just passing through our solar system. In fact, it’s the third confirmed interstellar object ever observed in our solar system. The previous two, 1I/ʻOumuamua (2017) and 2I/Borisov (2019), captured global attention. However, 3I/ATLAS stands out because it behaves like a comet, exhibiting a clear coma that indicates it releases gas and dust when warmed by the Sun.
Astronomers first spotted 3I/ATLAS on July 1, 2025. The discovery came through the ATLAS survey telescope (ATLAS), a facility focused on scanning the skies for dangerous asteroids, and sometimes catching surprises like this. Because of its interstellar origin, studying 3I/ATLAS gives scientists a rare, direct look at material formed around another star. It might even carry clues about how other planetary systems evolve.
Hubble’s new observation: A comet still active
When Hubble first imaged 3I/ATLAS in July 2025, the comet was already showing signs of activity. The images revealed a teardrop-shaped cloud of dust surrounding its icy nucleus.
The November 30 revisit showed that the comet remained active even as it raced away from the Sun. The images captured a bright central core enveloped in a diffuse coma, which seemed to spread outward in a slightly asymmetric way. The bright core is thought to mark the location of the comet’s solid nucleus, while the fuzzy halo is made of dust and gas released into space.
Because Hubble tracked the comet’s motion, the stars in the background streaked. That approach isolates the comet, making its subtle features easier to study. Analysts use such images to understand aspects like dust distribution and direction of gas jets.
Size, speed, and orbit of 3I/ATLAS
Astronomers still cannot pinpoint the exact size of 3I/ATLAS’s nucleus. But thanks to Hubble and other observatories, they have set limits. The nucleus may be as small as roughly 440 meters across, or as large as about 5.6 kilometres, quite a range, but useful for modelling how much material it can shed.
At the time of discovery, the comet was moving at about 137,000 miles per hour (roughly 221,000 km/h). As it passed near the Sun, its perihelion occurred around October 30, 2025, at about 1.4 astronomical units (AU), just outside Mars’s orbit. The gravity of the Sun and the comet’s own motion increased its speed even more.
Because of its hyperbolic orbit, 3I/ATLAS will not stay here. Its journey continues outward, back into deep space. And importantly, it poses no threat to Earth. At its closest, it will remain about 1.8 AU from our planet, too far to have any impact.
Questions still lingering
As exciting as the new images are, scientists remain careful. A glowing coma and dusty halo suggest normal comet behavior. But researchers still debate how exactly the dust and gas are released, and what that says about the comet’s internal makeup. For example, some recent polarimetry studies found that 3I/ATLAS shows very unusual light-scattering behavior, a deep negative polarization not seen in most comets.
That could signal a different surface structure or grain composition, maybe more like icy bodies beyond Neptune than traditional comets. Or, it might just reflect differences in how its dust and ice react to the Sun across interstellar origins.
Researchers also note that interpreting comet images requires caution. A diffuse halo might look dramatic, but it does not automatically imply unique physics. Simple explanations, outgassing of frozen ices, dust release due to solar heating, often suffice. Indeed, a NASA spokesperson recently reaffirmed that all available evidence shows 3I/ATLAS “looks and behaves like a comet.”
Astronomers plan to keep observing 3I/ATLAS for months to come. As it travels away from the Sun and back into interstellar space, its brightness, activity, and tail structure may change. Continued imaging and spectroscopy will help scientists refine estimates of its nucleus size, observe its gas and dust production, and study how its coma evolves.
Further reading
Right from the discovery of the interstellar comet 3I/ATLAS, DIYP has published several articles on its photographs and features. Here is the list of articles:
Clear skies!
