Strange Green Glow From Interstellar Comet 3I/ATLAS Has Scientists Puzzled

Images of interstellar comet 3I/ATLAS snapped during the September 7 full lunar eclipse look to suggest that the latest visitant to the Solar System whitethorn beryllium turning green.

That's not each that unusual for a comet. Many Solar System comets springiness disconnected a greenish glow erstwhile they vigor up capable to emit vapor. However, for 3I/ATLAS, it mightiness beryllium rather strange: observations of the comet's chemistry obtained to day amusement precise fewer signs of the dicarbon (C₂) molecules usually liable for a comet's greenish glow.

This could mean that the C₂ is there, but yet to beryllium detected. Or determination could beryllium different molecule liable for making the comet look green. Either way, the accusation is that the chemistry of 3I/ATLAS inactive has immoderate secrets it is yet to divulge.

Related: Images Show Interstellar Object 3I/ATLAS Is Now Growing a Tail

For the past fewer days, the interstellar comet 3I/ATLAS has been displaying a blue-green state coma measuring 2.5 arcminutes across. A abbreviated process was besides disposable connected September 9 erstwhile photographed with the 12"/f-3.6 astrograph successful Namibia. representation Gerald Rhemann, Michael Jäger pic.twitter.com/N3rXvYn3N8

The images were taken by astrophotographers Gerald Rhemann and Michael Jäger from Namibia during the full lunar eclipse that took spot connected the nighttime of 7 September 2025.

As a comet grows person to the Sun, the ices that are bound up astir its rocky nucleus statesman to sublime, turning into a state atmosphere, oregon coma. Molecules successful this gas, stimulated by star radiation, past fluoresce, glowing with airy successful a scope of visible, near-infrared, ultraviolet, and vigor wavelengths.

We cognize from JWST observations that 3I/ATLAS has a peculiar chemic creation that contains larger than accustomed proportions of c dioxide. Other observations truthful acold besides amusement the beingness of nickel and cyanogen. But these don't usually marque comets emit greenish fluorescence, and the molecule that does has not been found.

The occupation is adjacent thornier than a specified non-detection of C₂ mightiness indicate. According to a preprint led by astronomer Luis Salazar Manzano of the University of Michigan, Ann Arbor, the aboriginal detection of cyanogen implies a beardown depletion of carbon-chain molecules – including some C₂ and C₃.

"Our precocious bounds connected the C₂-to-CN ratio," they write, "places 3I/ATLAS among the astir carbon-chain depleted comets known."

So there's a fascinating enigma there. Here's hoping our scientists tin cod capable information to lick it erstwhile the comet makes its closest walk to Earth successful December.