Interstellar Visitor 3I/Atlas Caught by NASA’s Punch Mission During Comet Swan Monitoring

NASA’s Punch mission has recorded the unexpected appearance of interstellar object 3I/Atlas while conducting long-duration observations of Comet C/2025 R2 (Swan). Known for studying the solar wind and solar activity, the Punch spacecraft captured images of the comet every four minutes for nearly 40 days, providing one of the most detailed datasets of a comet near the Sun.

During this intensive observation period, scientists noticed 3I/Atlas briefly crossing the field of view—a rare chance to observe an object from beyond our solar system in routine imaging. A mission scientist noted, “Interstellar objects pass quickly, and capturing one in routine imaging is rare.”

The high-frequency images allowed the team to track changes in Comet Swan’s coma and tail with unprecedented detail. Craig DeForest, principal investigator of Punch, explained, “relied on steady and repeated imaging to capture events that usually go unseen.”

3I/Atlas entered the frame from the left and moved across the lower section while Comet Swan continued along its path near perihelion. Unlike the comet, which follows an orbit shaped by the Sun’s gravity, 3I/Atlas moves at high speed along a trajectory that indicates it came from outside the solar system and will continue outward. Another team member said the event “added context to the dataset and helped show how different bodies react to the solar environment.”

While the interstellar visitor grabbed attention near the end of the observation timeline, most of the mission focused on Comet Swan. The comet’s coma brightened over the weeks and later developed a triangular, hammer-like shape—patterns linked to outgassing from multiple points in its nucleus. Scientists explained that these changes “can happen when parts of the nucleus begin to break away.” The Sun’s heating caused ice to sublimate into gas, which, along with dust pushed by the solar wind, shaped the comet’s tail.

The Punch mission’s rapid imaging sequence allowed researchers to monitor Comet Swan almost hour by hour, rather than day by day, providing a comprehensive baseline to compare the movement and behavior of 3I/Atlas. This simultaneous observation of a comet and an interstellar object offers a unique opportunity to study how different bodies respond to the solar environment.

Amateur astronomer Vladimir Bezugly first spotted Comet Swan in data from the SOHO spacecraft, noting a bright point near the Sun. The comet reached its closest approach just one day after discovery, and the Punch mission’s extensive dataset now provides one of the most detailed records ever collected for a comet near perihelion.