What We Know About Interstellar Comet 3I/ATLAS

NASA Jet Propulsion Laboratory

We have another mysterious comet in the solar system, this one much closer to the Sun than the huge one near Neptune, 3I/ATLAS has already passed Jupiter and should make closest approach in October at about the same orbit as Mars. Hopefully we should be able to get some decent images as this wanderer will not be back.

4 Jul 2025

An interstellar traveler has been discovered passing through our solar system. The NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile, first reported observations of comet 3I/ATLAS on July 1, 2025. Since the first report, additional observations from before the discovery were gathered from the archives of three ATLAS telescopes around the world and Caltech’s Zwicky Transient Facility at the Palomar Observatory in San Diego County, California. These “pre-discovery” observations extend back to June 14. The fast-moving comet, which originated outside our solar system around a different star, was discovered as a tiny speck moving across the vastness of space. When discovered it was about 410 million miles (670 million kilometers) away from the Sun, within the orbit of Jupiter.

This is the third interstellar object ever discovered, hence its name begins with the number 3 and the letter I. Scientists will have several months to observe and study the comet as it passes through our solar system and before it exits. As of July 3, 2025, the comet is just inside the orbit of Jupiter and in late October 2025 it will make its closest approach to our sun from just inside the orbit of Mars. It poses no threat to Earth but offers a fascinating and rare opportunity for scientists to study these interstellar interlopers.