Comet 3I/ATLAS

Overview

Comet 3I/ATLAS is the third known object from outside our solar system to be discovered passing through our celestial neighborhood. Astronomers have categorized this object as interstellar because of the hyperbolic shape of its orbital path. (It does not follow a closed orbital path about the Sun.) When the orbit of 3I/ATLAS is traced into the past, the comet clearly originates from outside our solar system.

Comet 3I/ATLAS poses no threat to Earth and will remain far away. The closest it will approach our planet is about 1.8 astronomical units (about 170 million miles, or 270 million kilometers). 3I/ATLAS will reach its closest point to the Sun around Oct. 30, 2025, at a distance of about 1.4 au (130 million miles, or 210 million kilometers) — just inside the orbit of Mars.

The interstellar comet’s size and physical properties are being investigated by astronomers around the world. 3I/ATLAS should remain visible to ground-based telescopes through September 2025, after which it will pass too close to the Sun to observe. It will reappear on the other side of the Sun by early December 2025, allowing for renewed observations.

Discovery

The NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile, first reported observations to the Minor Planet Center of comet 3I/ATLAS on July 1, 2025. Since the first report, observations made before the discovery were gathered from the archives of three different 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, 2025.

How this comet got its name: Comets are generally named for their discoverer(s), in this case the ATLAS survey team. The letter “I” is for “interstellar,” indicating that this object came from outside our solar system. It’s the third known interstellar object, hence the “3” in the name.

Read more about NASA's discovery of comet 3I/ATLAS

NASA Assets Observing Comet 3I/ATLAS

NASA's Hubble Space Telescope captured this image of interstellar comet 3I/ATLAS on July 21, 2025, when the comet was 277 million miles from Earth. Hubble revealed a teardrop-shaped cocoon of dust coming off of the comet's solid, icy nucleus. Because Hubble was tracking the comet moving along a hyperbolic trajectory, the stationary background stars are streaked in the exposure. Hubble’s continuing observations allow astronomers to more accurately estimate the size of the comet’s nucleus. Observations as of Aug. 20, 2025, indicate that the upper limit on its diameter is 3.5 miles (5.6 kilometers), though it could be as small as 1,444 feet (440 meters) across. 

NASA assets that are gathering observations of 3I/ATLAS include: Hubble, Webb, TESS, Swift, SPHEREx, Perseverance Mars rover, MRO (Mars Reconnaissance Orbiter), MAVEN (Mars Atmosphere and Volatile EvolutioN), Europa Clipper, Lucy, Psyche, Parker Solar Probe, PUNCH, and ESA/NASA’s SOHO.

Check back here for observations, schedules, or any additional NASA assets, as that information becomes available.

Read more about the Hubble image