In a lucky break for science, NASA’s PUNCH mission got more than it bargained for. The mission was busy taking a detailed time-lapse of a comet when an unexpected guest zoomed into view. The visitor was an interstellar object named 3I/Atlas. This object comes from outside our solar system.
This surprise sighting happened on Tuesday, March 25, 2025. The PUNCH mission was already watching a different comet called C/2025 R2 (Swan). The spacecraft takes a picture every four minutes to track changes. After nearly 40 days of this, scientists spotted something new in the final images.
What the PUNCH Mission Saw
The main goal was to study Comet Swan. The high-frequency photos created an extremely detailed movie. This showed the comet’s bright cloud (coma) and tail changing shape from day to day. Scientists think these changes might mean the comet’s icy core was cracking apart.
Then, the interstellar object 3I/Atlas appeared. It moved quickly in a straight line at the bottom of the frame. It passed underneath Comet Swan’s path.
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Comet Swan: A local comet, orbiting our Sun. It was being shaped by the Sun’s heat and gravity.
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3I/Atlas: An interstellar visitor. It is just passing through our solar system on its own path from deep space. It does not orbit our Sun.
“It’s a remarkable coincidence of timing,” said a mission scientist. “Interstellar objects travel fast. Capturing one during routine observations is very rare.”
Why This Sighting is Important
Catching 3I/Atlas was a bonus. It gives scientists a unique opportunity. They can now directly compare how two very different objects behave in the same environment near the Sun.
The dataset now tells two stories at once:
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A detailed look at a comet changing in real-time.
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A clear record of an interstellar object’s speed and trajectory as it passes by.
This helps astronomers understand the differences between objects born in our solar system and visitors from other stars.
