Interstellar Comet 3I/ATLAS Displays Unexpected Blue Glow as it rounds the Sun
Astronomers are puzzled by a striking blue hue detected in interstellar comet 3I/ATLAS,a phenomenon differing from previous observations which showed the comet’s dust as reddish. The unusual coloration, observed as the comet passed near the Sun, is suspected to be caused by emissions from molecules like cyanogen and possibly ammonia.
This comet, originating from outside our solar system, has captivated scientists since it’s revelation. Its recent close approach to the Sun – reaching perihelion on October 29 – triggered a dramatic brightening, potentially to magnitude 9, making it visible through smaller amateur telescopes. The blue glow adds another layer of intrigue to this rare opportunity to study an interstellar object up close.
Observations from GOES-19‘s coronagraph revealed 3I/ATLAS as an extended object with a visible coma, a glowing envelope of gas and dust surrounding the nucleus. This confirms the comet is actively shedding material as it’s heated by the Sun. Earlier observations had found the comet’s dust to be reddish, making this blue shift notably noteworthy.
Researchers are currently investigating the cause of the rapid brightening and the unusual blue coloration. Theories include the comet’s unique composition,its high approach speed,or characteristics acquired during its journey through interstellar space.
As 3I/ATLAS emerges from behind the Sun and enters darker skies in November and December, ground-based observers will have a prime opportunity to study this interstellar visitor in detail. A preprint of the research is available on arXiv: https://arxiv.org/abs/2510.25035.
(Image credit: NOAA/Lockheed Martin)
