Rapid Brightening of Interstellar Comet 3I/ATLAS As It Nears Sun Surprises Scientists
Left: Stack of all CCOR-1 frames of 3I/ATLAS (top), and an equivalent stack centered on a nearby star on the same frames, approximating the PSF (bottom). Right: Similar stacks of all HI1 (top), COR2 (middle), and LASCO C3 Clear (bottom) frames of 3I. All stacks are aligned with north up. The heliocentric velocity (+v), and sunward (⊙) or antisunward (−⊙) directions are labeled for the comet at the midpoint time. Credit: arXiv (2025). DOI: 10.48550/arxiv.2510.25035
An interstellar comet that originated outside our solar system has just made its closest pass to the sun, brightening dramatically and rapidly as it did so. The reason for the sudden extreme activity is currently puzzling scientists.
The latest visitor to our corner of the galaxy was first spotted on July 1, 2025, by astronomers and officially named comet 3I/ATLAS. It’s only the third interstellar comet ever recorded and was calculated to be on a course that would take it close to the sun without plunging into it.
As the object neared its closest point to our star (perihelion), the immense solar glare made it virtually impossible for Earth-based telescopes to see it. So astronomers turned to space-based solar observatories like SOHO, STEREO-A and GOES-19 to keep a watchful eye.
In a paper published on the arXiv preprint server, researchers confirmed that as the comet closed in on the sun, it was brightening at a steeply accelerating rate. This surge was more extreme than had ever been observed in a comet before. These icy bodies usually brighten slowly as they heat up. The comet also appeared blue, which surprised scientists as comets are typically red owing to dust reflecting sunlight.
“Our cursory analysis of this data indicates the comet will likely emerge from conjunction considerably brighter than when it entered, with an extrapolated geocentric V magnitude of ∼9 at perihelion, perhaps driven by prominent, visible gas emission,” wrote the researchers in their paper.
(Source: phys.org)
