Interstellar visitor 3I/Atlas makes surprise appearance in NASA’s Punch observations

Interstellar Visitor 3I/Atlas Appears in Punch Mission Timeline opens with the unexpected sighting of 3I/Atlas during NASA’s long-duration monitoring of Comet C/2025 R2 (Swan).

The Punch mission, known for tracking the solar wind and activity around the Sun, recorded images of the comet every four minutes for nearly 40 days.

During this period, scientists noticed a brief crossing of 3I/Atlas, an object that originated outside our solar system.

This moment added new scientific interest to a data set already seen as important for understanding how comets behave near the Sun.

The mission team explained that the high-frequency images allowed them to follow changes in the comet’s coma and tail with unusual detail.

Craig DeForest, principal investigator of Punch, said the mission “relied on steady and repeated imaging to capture events that usually go unseen.”

Scientists also noted that the comet’s shape shifted over the weeks, which may point to fragmentation inside the nucleus.

The appearance of 3I/Atlas was recorded near the end of the timeline, moving quickly beneath Comet Swan.

The dataset now offers two parallel stories: a comet undergoing rapid changes and an interstellar object passing through the field of view at the right moment for observation.

How did 3I/Atlas enter the frame?

The Punch mission’s images show 3I/Atlas entering the field from the left and moving across the lower section of the frame as Comet Swan continued its path.

Scientists described the event as a coincidence of timing, but one that gave them a chance to compare the movement of two different kinds of objects. A mission scientist noted that “interstellar objects pass quickly, and capturing one in routine imaging is rare.”

Researchers explained that 3I/Atlas does not follow the same type of orbit as objects that form inside the solar system. Its speed and direction suggest it entered from outside and will continue outward.

By contrast, Comet Swan was near perihelion when the mission began tracking it, moving along a path shaped by the Sun’s gravity.

Another member of the team said the sighting “added context to the dataset and helped show how different bodies react to the solar environment.”

The mission's steady image sequence allowed the team to see the straight motion of 3I/Atlas compared with the changing look of Comet Swan.

This difference helped them outline how interstellar visitors behave when they pass near the Sun, even for only a short time.

Comet Swan’s behaviour during the observation period 

While 3I/Atlas drew attention near the end of the timeline, most of the Punch mission’s work centered on Comet Swan. Images showed the coma becoming brighter and later taking on a triangular, hammer-like shape.

Scientists link this pattern to outgassing from several points within the nucleus. One researcher said the pattern “can happen when parts of the nucleus begin to break away.”

The coma formed as the Sun heated the comet, causing ice to turn directly into gas.

Dust and gas pushed outward by the solar wind created the tail. Over the weeks, the changing shape suggested the comet was reacting strongly to the Sun’s energy.

Swan was first spotted by amateur astronomer Vladimir Bezugly, who noticed a bright point near the Sun in data from the SOHO spacecraft. It reached its closest point to the Sun just one day after that discovery.

The Punch mission’s rapid imaging produced a long sequence of data, which scientists say may be among the most frequent observations ever collected for a comet.

This allowed them to follow changes hour by hour rather than day by day. When 3I/Atlas entered the view, the mission already had a baseline for comparison.
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