Scientists have observed that the interstellar comet 3I/ATLAS has turned blue, marking its third color change since discovery.
3I/ATLAS, recorded as the third interstellar visitor observed by humanity, entered the solar system at a speed of 58 km/s (210,000 km/h) and is believed to have traveled the outer regions of the Milky Way for over 7 billion years.
Discovered in July, the comet passed near Mars in early October and went behind the Sun, making it temporarily invisible from Earth. It is now visible again.
The comet initially appeared red, likely due to dense dust ejected from its surface. In September, it glowed green, suggesting gases like cyanide or diatomic carbon (C₂) in its atmosphere. Recent observations show a bluish tint, probably caused by carbon monoxide or ammonia emissions, though these findings are yet to undergo peer review.
3I/ATLAS reached its closest point to the Sun (130 million miles / 210 million km) on October 29, triggering a sudden flare and brightness increase. Scientists have yet to explain this phenomenon, as proximity to the Sun alone should not trigger such a strong reaction.
In the coming weeks, the comet will become visible through telescopes in the Northern Hemisphere, though not to the naked eye. It will reach its closest point to Earth (270 million km) on December 19.
The European Space Agency (ESA) may send two spacecraft through the comet's tail during this period, offering a rare opportunity to directly measure its composition.
3I/ATLAS has displayed unusual characteristics: a high carbon dioxide content, excessive water vapor release, and a reversed "anti-tail." These anomalies have led some researchers to speculate about an artificial origin, though most scientists believe it behaves like a normal comet.
