A mysterious interstellar object, 3I/ATLAS, is making its way through the Solar System and heading toward a historic rendezvous. Scientists predict that within the coming weeks, the object will pass close to NASA’s Europa Clipper and the European Space Agency’s (ESA) Hera spacecraft. The encounter, expected between October 25 and November 6, 2025, could mark the first-ever direct observation of an “interstellar comet’s ion tail.”
According to preliminary studies, both spacecraft might enter the ion tail of 3I/ATLAS, allowing humanity to study charged particles originating from beyond our Solar System for the first time. The ion tail—stretching millions of kilometers from the comet’s core—contains valuable information about the composition of matter outside our cosmic neighborhood.
These predictions come from a European-developed software tool called Tailcatcher, designed to calculate a spacecraft’s closest approach to a comet’s ion tail using solar wind data. Current models suggest that 3I/ATLAS will pass within roughly 8 million kilometers of the spacecraft. Although Europa Clipper may not measure all ion components, scientists expect it to gather crucial data on the structure and chemistry of the comet’s tail.
Discovered in July 2025 and estimated to be the size of a small city, 3I/ATLAS has sparked both scientific curiosity and extraterrestrial speculation. Harvard astrophysicist Avi Loeb reignited debates by suggesting the object might be artificial in origin, further fueled by his cryptic reference to October 29.
Recent observations from Hawaii’s Keck II Telescope revealed an unusual “anti-tail” stretching toward the Sun—an anomaly rarely seen in comets. Some researchers believe this could be an optical illusion caused by Earth’s position, while others suspect large dust grains resisting solar wind pressure.
In response to these anomalies, the International Asteroid Warning Network (IAWN) has added 3I/ATLAS to its special observation list—the first time an interstellar object has been included. Between November 27, 2025, and January 27, 2026, telescopes worldwide will participate in a coordinated campaign to track this mysterious cosmic traveler.