Interstellar Comet Nears Earth With Unusual Anti-Tail

NASA and ESA are tracking 3I/ATLAS, only the third confirmed interstellar visitor, as images highlight a striking anti-tail caused by viewing geometry and dust.​

Lead

A rare interstellar comet, officially named 3I/ATLAS, is making its closest approach to Earth on about Dec. 19, 2025—still a safe distance away—while drawing attention for an unusual-looking anti-tail that can appear to point sunward.​

NASA says the comet will pass closest to Earth at roughly 170 million miles (about 269 million kilometers), and multiple NASA missions and telescopes have been observing it across the solar system.​

ESA, which began tracking the object soon after discovery, has emphasized that the comet poses no danger to Earth and represents a rare chance to study material from another planetary system.​

Key facts and timeline

Astronomers first reported 3I/ATLAS on July 1, 2025, after detection by the NASA-funded ATLAS survey telescope in Río Hurtado, Chile, and follow-up work quickly confirmed an interstellar trajectory.​

The comet is the third confirmed interstellar object observed in the Solar System, following 1I/ʻOumuamua (2017) and 2I/Borisov (2019), making it a high-priority target for planetary science.​
NASA’s Planetary Defense blog reported early on that the comet would stay at least about 1.6 astronomical units from Earth and reach closest approach to the Sun around Oct. 30, 2025, at about 1.4 AU—just inside Mars’ orbital distance.​

ESA has also published early estimates suggesting the comet could be up to about 20 km wide and moving roughly 60 km/s relative to the Sun, while stressing that such physical estimates can evolve as observations improve.​

NASA has similarly said that the object’s size and physical properties are under investigation by astronomers worldwide.​

Why the anti-tail looks strange

Comets usually show tails pointing away from the Sun because sunlight and the solar wind push dust and ionized gas outward, producing the classic anti-solar direction.​

An anti-tail (also called an antitail) is different: it is typically made of relatively larger dust grains that stay closer to the comet’s orbital plane and can create the illusion of a sunward-pointing spike when viewed from certain angles.​

This is mainly a perspective effect—when Earth’s line of sight aligns with the comet’s orbital plane, the dust distribution can look like a narrow feature pointing toward the Sun even though the particles are not actually streaming sunward.​

In other words, the unusual anti-tail does not require exotic physics: it can happen when geometry briefly makes a dust sheet or dust trail appear edge-on from Earth’s viewpoint.​

Skywatchers may see multiple tail-like structures at once because dust and gas respond differently to sunlight and the solar wind, so features can point in slightly different directions.​

What NASA and ESA are watching

NASA says it is conducting a wide-ranging observation campaign and that 12 NASA assets have captured and processed imagery of 3I/ATLAS since discovery, with more opportunities expected as it continues through the Solar System.​

According to NASA, some of the closest spacecraft imagery came from Mars, where the comet passed by at a distance of about 19 million miles and was observed by multiple Mars missions, including Mars Reconnaissance Orbiter and MAVEN.​

NASA also reports that heliophysics missions tracked the comet near the Sun—an area where ground-based observing can be difficult—using missions such as STEREO and the ESA/NASA SOHO observatory, and that this was the first time NASA’s heliophysics missions intentionally observed an object from another solar system.​

ESA’s Planetary Defence Office has described its role as rapid tracking and characterization support, including precovery searches in older data and coordination across telescope networks in places like Hawaii, Chile, and Australia.​

ESA also highlights why these efforts matter: interstellar objects are outsiders that can carry chemical and physical clues about planet formation beyond the Solar System.​

What comes next (and what readers should know)

For most people, 3I/ATLAS is not a naked-eye object; the practical takeaway is that it remains far from Earth, scientifically valuable, and visually interesting mainly through telescopes and processed images—especially when tail geometry becomes favorable.​

NASA’s latest Earth-close-approach figure—about 170 million miles on or about Dec. 19—underscores that the comet is nowhere near an impact scenario.​

As it continues outward toward spring 2026, researchers will keep comparing its dust and gas behavior to home-grown comets to see what differs when a comet formed around another star.