Interstellar Comet 3I/ATLAS baffles astronomers with sudden speed, blue glow and missing tail

Interstellar Comet 3I/ATLAS Shows Mysterious Blue Tint After Sudden Brightening (Image: NASA/ESA)

Astronomers worldwide are watching a mysterious cosmic traveller named 3I/ATLAS. The interstellar object has startled experts with a sudden burst in speed and a striking shift in colour as it nears the Sun. First spotted in July by a telescope in Chile, it is only the third known visitor from outside our solar system after ‘Oumuamua and Borisov. NASA has confirmed that it poses no danger to Earth and will pass about 269 million kilometres away in December.

On 29 October, 3I/ATLAS appeared like a comet but soon brightened and turned a noticeable shade of blue. NASA scientists said its speed has risen to about 2,44,600 kilometres per hour, with a small but unexplained acceleration not caused by the Sun’s gravity alone.

Davide Farnocchia, a navigation engineer at NASA’s Jet Propulsion Laboratory, described this as a case of “non-gravitational acceleration.” Harvard astrophysicist Avi Loeb suggested that the push may come from gases and dust escaping the comet’s surface. “As it expels this material faster, it gets kicked back,” Loeb explained in his blog. He estimated that 3I/ATLAS might lose nearly one-tenth of its total mass within a month.

In an interview with NBC News, Loeb added that the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile observed a deviation of four arcseconds from the predicted path. “That’s very significant statistically,” he said, suggesting that the change could mean “the evaporation of about a sixth of its mass.” Loeb predicted that this “massive mass loss” would likely form a visible gas plume around the comet in November and December.

Observers also noticed that the comet seemed to shift colour as it neared the Sun. Some reports claimed multiple colour changes, but Qicheng Zhang from Lowell Observatory clarified this view. “We don’t have evidence for the gas coma changing colours,” he told Space.com.

Zhang said the comet appeared to change once when gases first became visible. “It’s still like that now, only brighter,” he added. According to Zhang, amateur photographs from early September already showed a blue-green glow forming around the comet.

Loeb, who has previously discussed artificial origins for interstellar objects, said the unusual acceleration might point to a technological cause. “It could be the signature of an internal engine,” he told NBC News. He also noted that the blue colour might indicate “a hot engine or artificial light,” though he still leans towards a natural explanation involving ionised carbon monoxide.

In a surprising turn, new images revealed that 3I/ATLAS lost its tail after passing close to the Sun. Typically, solar heat makes comets release gas and dust that form bright tails, but this one disappeared instead. Loeb said about 13 per cent of its mass should have appeared as a tail, yet “no such tail is visible.”

NASA and the European Space Agency plan to continue monitoring 3I/ATLAS as it travels toward Jupiter in March 2026.

The object was named after the ATLAS survey team in Río Hurtado, Chile, which detected it on 1 July. The “I” in its name stands for “interstellar,” showing that it comes from outside our solar system, while the “3” identifies it as the third such object ever recorded.

As astronomers watch its next moves, 3I/ATLAS continues to raise new questions about the visitors that cross our solar system from the depths of interstellar space.

Astronomers worldwide are watching a mysterious cosmic traveller named 3I/ATLAS. The interstellar object has startled experts with a sudden burst in speed and a striking shift in colour as it nears the Sun. First spotted in July by a telescope in Chile, it is only the third known visitor from outside our solar system after ‘Oumuamua and Borisov. NASA has confirmed that it poses no danger to Earth and will pass about 269 million kilometres away in December.