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As excitement builds across the astronomy community, experts say the mysterious interstellar comet 31/ATLAS will pass Closest to Earth in December. This is a rare opportunity for scientists and skywatchers alike.

A Rare Interstellar Visitor will be closest to Earth in December

December is the month that fans of the 3I/ATLAS interstellar comet have been waiting for. In a matter of days, the strange space object — only the third confirmed interstellar visitor in history — is expected to pass closest to Earth in December 2025, offering its best visibility window for the next several million years.

Though not bright enough to see with the naked eye, NASA says 3I/ATLAS can be viewed with a small telescope through spring 2026. The agency’s real-time simulator, Eyes on the Solar System, tracks the comet’s exact position and trajectory:

Eyes - NASA Science

“This is an extraordinary chance to observe an object formed around another star,” one NASA researcher noted. “These encounters are exceedingly rare in human history.”

Details from NASA about 31/ATLAS

The interstellar comet known as 3I/ATLAS made global headlines in July when astronomers confirmed that it originated outside our solar system. When first detected, it was racing through the void at an incredible 137,000 mph, according to NASA:

🔗 https://www.nasa.gov/

Its speed, hyperbolic trajectory, and approach path from the direction of the constellation Sagittarius offered definitive proof that it formed around another star before being ejected into deep interstellar space.

By December 19, 2025, it will pass within 170 million miles of Earth— roughly twice the distance between Earth and the Sun — and well above any threat threshold.

The comet also made a close pass of the Sun on October 30, coming within 130 million miles, just inside the orbit of Mars.

See first images from Vera C. Rubin Observatory

How Big Is the Interstellar Comet?

Although its exact size remains uncertain, the European Space Agency estimates the object could span hundreds of feet to several miles across.

According to Hubble Space Telescope observations, the comet’s icy nucleus may be anywhere from 1,400 feet to 3.5 miles wide — still small compared to typical solar system comets but enormous as a wandering interstellar object.

31/ATLAS, Jupiter, and Perihelion: Scientists Race to Decode Interstellar “Heartbeat” Ahead of Its Close Approach - USA Herald

How to See 3I/ATLAS in December

NASA confirms that 3I/ATLAS is visible in the pre-dawn sky, but only through telescopes or high-end binocular systems.