Astronomers spot unusual 'anti-tail' on interstellar comet 3I/ATLAS
Astronomers just spotted something unusual on the interstellar comet 3I/ATLAS—a sunward "anti-tail."
Using the Keck II telescope in August 2025, they found this real dust plume stretching toward the Sun, along with a rare dominance of nickel emission (without iron), and cyanide emissions, a combination not usually seen in local comets.
How does the anti-tail form?
The anti-tail forms when larger ice grains on the sunny side of the comet last longer and create a dust stream pointing at the Sun.
It's not an optical trick—models show this structure matches what astronomers observed.
Observing the comet
Right now, 3I/ATLAS is about 3.8 astronomical units from Earth and racing through space at 209,000km/h.
It's too faint for the naked eye but can be seen with a decent telescope under dark skies.
The comet is currently in Sagittarius and will swing closest to the Sun on October 29, 2025.