Fastest comet 3I/ATLAS exits solar system: Could Earth be at risk?
Comet 3I/ATLAS departure and its danger to Earth (photo: Getty Images)
After months of observations, astronomers bid farewell to 3I/ATLAS. This icy rock, first spotted in July 2025, became only the third interstellar object in the history of our solar system. Scientists confirmed that it is the fastest comet ever recorded, covered with icy volcanoes, and is definitely not an alien spacecraft.
Popular Science explains where comet 3I/ATLAS goes, whether it threatens Earth, and what surprise it leaves behind.
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A delayed outburst: why the comet flared as it departed
Even though 3I/ATLAS is moving away from Earth at 130,000 miles per hour, it continues to astonish. In December 2025, NASA’s SPHEREx observatory recorded a sudden spike in brightness two months after it passed the Sun.
"Comet 3I/ATLAS was full-on erupting into space in December 2025, after its close flyby of the sun, causing it to significantly brighten. Even water ice was quickly sublimating into gas in interplanetary space," explains astrophysicist Carey Lisse.
Since roughly one-third of the object is ice, solar heating released carbon-rich material that had been trapped deep below the surface for billions of years.
A chemical cocktail: from methane to cyanide
SPHEREx data revealed a change in the comet’s composition:
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August 2025: Dominated by carbon dioxide, carbon monoxide, and water.
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December 2025: After heating, it ejected a mixture containing cyanide, methane, methanol, and rocky debris.
Scientist Phil Korngut explains the delayed eruption with a thick cosmic crust. The comet had been exposed to radiation in interstellar space for centuries, and it took the Sun some time to penetrate this layer and warm the untouched inner ices.
Does it pose a threat to us now?
Although the eruptions look dramatic, there is no direct threat to Earth. The object has already passed its closest point to us and is heading rapidly into deep space. Gas emissions occur at a safe distance but provide scientists with unique data about the composition of other worlds, which will be studied for decades to come.
The uniqueness of 3I/ATLAS: astonishing facts
This is only the third known interstellar object in observation history, and it has already set several records:
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Fastest: Officially the fastest comet ever recorded by astronomers.
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Icy volcanoes: Its surface is covered with cryovolcanoes, making it resemble an active geological world.
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Not a UFO: Scientists have confirmed that it is a natural space rock, not a vessel for alien tourists.
