Here are some quick facts about 3I/ATLAS ahead of its closest approach to Earth

A rare visitor from deep space reaches a major milestone on December 19: Comet 3I/ATLAS will make its closest approach to Earth at 1 a.m. EST (6 a.m. GMT). Discovered in July by the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Chile, there are a number of reasons why this icy traveler stands out. Let's take a look at some of them.

Interstellar origin 

This is only the third interstellar object on record to have originated from outside our solar system, following on the heels of the famous 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019. Its arrival in our neighborhood has given us a rare opportunity to study the chemistry of a distant, alien star system, per the ESA. 

Record-breaking speed 

When it was discovered, 3I/ATLAS was zooming through space at the speed of about 137,000 miles per hour (221,000 kilometers per hour), per NASA. And once it came within the reach of our Sun's gravity, its speed increased to about 153,000 miles per hour (246,000 kilometers per hour), which, according to the ESA, is the highest ever recorded speed for an object visiting our solar system.

Massive age 

By its extreme velocity and angle of entry, astronomers estimate the comet is billions of years old, perhaps having predated our own solar system and having spent ages drifting amidst the vast, empty "void" between stars. 

Size 

Based on the observations made by the Hubble Space Telescope on August 20, 2025, its size is estimated to be anywhere from 1,400 feet (440 meters) to 3.5 miles (5.6 kilometers) wide. 

Distance on December 19

At its closest approach on December 19, 3I/ATLAS will be within 170 million miles (270 million kilometers) away from Earth. That is about 1.8 astronomical units, nearly twice the distance between Earth and the Sun. 

One-way trip 

The comet happens to be on what has been defined as a hyperbolic trajectory. Since its speed is too high for it to be captured in a permanent orbit by the Sun's gravity, it will just slingshot around our star and head back into interstellar space, never to be seen again.

Galactic direction

Scientists think that the comet came from the general direction of the constellation Sagittarius, which is situated roughly in the direction of the Milky Way's center. When it was discovered, it was about 410 million miles (670 million kilometers) from the Sun, in the orbit of Jupiter.

Although the comet is indeed making its "closest approach" to our planet, NASA stresses that it will not be a "naked-eye" spectacle for casual viewers, despite being a significant scientific event. A dark sky and a telescope with an aperture of at least 30 centimeters (12 inches) are required to see it. The comet will be visible in the east-northeast sky, directly beneath Regulus, the brightest star in the center of the constellation Leo. 

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