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Like a message in a bottle slipping past Earth, an interstellar comet may still be whispering clues about its origins before vanishing forever beyond the Sun’s reach. NASA scientists are racing to decode those signals as new observations sharpen the focus on comet 3I/ATLAS — a rare visitor from another star system.

TESS Turns Its Gaze From Planets to a Cosmic Wanderer

NASA’s planet-hunting Transiting Exoplanet Survey Satellite (TESS) recently captured an unexpected target: interstellar comet 3I/ATLAS. During a dedicated observation window from Jan. 15 through Jan. 22, TESS repeatedly monitored the comet as it sped outward from the solar system.

With its sweeping field of view, the spacecraft tracked the object as a luminous, fast-moving speck, trailing a delicate tail like chalk dragged across a blackboard of densely packed stars.

A 28-Hour Movie — With a Missing Scene

Using data from earlier January observations, Daniel Muthukrishna of the Massachusetts Institute of Technology stitched together the images into a 28-hour video that traces the comet’s path. The footage, however, is not seamless. TESS briefly entered “safe mode” after a problem with its solar panels, creating a noticeable jump in the timeline between Jan. 15 and Jan. 18.

Even so, the dataset is a scientific gold mine. Researchers hope NASA 3I/ATLAS comet spin gauging will reveal how actively the object is releasing dust and gas, and how fast its icy core is rotating — vital clues to understanding its physical makeup.

Brightness, Motion and a Mission With Side Benefits

TESS measurements place the comet’s brightness at an apparent magnitude of about 11.5, roughly 100 times dimmer than what the human eye can detect, but well within the reach of telescopes.

Although TESS was designed to discover exoplanets by detecting tiny dips in starlight as planets pass in front of distant suns, its wide-angle vision and steady monitoring make it surprisingly effective at tracking nearer objects. Comets and asteroids, it turns out, can also leave detectable fingerprints in its data.

Found Before It Was Known

That capability paid off in a remarkable way. TESS had already observed comet 3I/ATLAS back in May 2025 — nearly two months before astronomers officially identified it. By combing through archived data and stacking multiple observations, scientists were able to isolate the interstellar traveler from background noise and reconstruct its motion.

While the technique cannot pinpoint where the comet came from, it does provide crucial insights into its behavior and structure.

Public Data, Fleeting Opportunity

The January observations are now publicly available through the Mikulski Archive for Space Telescopes. Within these limited hours of data, astronomers are searching for repeating brightness patterns that could unlock more secrets before the comet slips back into interstellar darkness.

For now, NASA 3I/ATLAS comet spin gauging stands as a reminder that even missions built to hunt distant worlds can, by chance, illuminate a fleeting visitor from beyond the stars.