NASA exoplanet probe tracks interstellar comet 3I/ATLAS to gauge its spin

A streaking white comet moves to the left of the image with a boxout showing a floating metal spacecraft with two opposing solar panels in space

NASA's planet-hunting TESS (Transiting Exoplanet Survey Satellite) spacecraft recently caught a glimpse of interstellar comet 3I/ATLAS. (Image credit: TESS insert by NASA/comet background by Enrico Bellodi from Pexels/assembled by Kenna Hughes-Castleberry via Canva pro)

NASA's planet-hunting TESS spacecraft recently caught a view of a very different kind of cosmic object: interstellar comet 3I/ATLAS.

During a special observation run from Jan. 15 to Jan. 22, the Transiting Exoplanet Survey Satellite (TESS) repeatedly observed comet 3I/ATLAS as it headed out of our solar system. With its wide field of view, TESS recorded the comet as a bright, fast-moving dot dragging a faint tail across a crowded starfield.

Using data from some of earlier January observations, Daniel Muthukrishna of the Massachusetts Institute of Technology (MIT) compiled the images into a 28-hour video that shows comet 3I/ATLAS's trajectory. Unfortunately, TESS' observations were interrupted when the spacecraft entered "safe mode" after experiencing an issue with its solar panels, so the video includes a time jump from Jan. 15 to Jan. 18.

A moving graph showing pixels on both the X and Y axis and a busy white dotted starfield in the center of the GIF. A red circle follows a bright moving dot as it moves through the starfield — Interstellar comet 3I/ATLAS (circled) is a bright dot with a tail passing through a field of stars in this video from NASA’s TESS (Transiting Exoplanet Survey Satellite). The sequence uses 28 hours of TESS full frame images collected over Jan. 15 and Jan. 18 to 19. The time jump from Jan. 15 to Jan. 18 occurs 11 seconds into the video. (Image credit: NASA/Daniel Muthukrishna, MIT)

Scientists like Muthukrishna hope to use the dataset to study the comet's activity and rotation, clues that reveal how vigorously it's shedding dust and gas and how quickly the comet's core spins.

TESS measurements put comet 3I/ATLAS's brightness at about 11.5 in apparent magnitude, roughly 100 times fainter than what we can see with the naked eye, but accessible using telescopes.

NASA's TESS mission was designed to find exoplanets via the transit method, in which a faraway star dims slightly when a planet in its system passes in front of it. But TESS' wide field of view and consistent monitoring also make it useful for detecting and tracking closer objects, including comets and asteroids, for longer stretches of time.

This capability helped astronomers spot comet 3I/ATLAS before they even knew it was there. TESS happened to observe a comet in May 2025, two months before 3I/ATLAS was discovered. By looking back through all the data and compiling multiple observations, astronomers could filter out the interstellar visitor through the noise and track its movements. While unfortunately this doesn't tell us where the comet originated, it does give us other key details.

The January TESS observations are now publicly available and can be found on the the Mikulski Archive for Space Telescopes. It's within these precious hours that astronomers may find repeating patterns of brightness that reveal further secrets about our brief interstellar visitor.

Kenna Hughes-Castleberry is the Content Manager at Space.com. Formerly, she was the Science Communicator at JILA, a physics research institute. Kenna is also a freelance science journalist. Her beats include quantum technology, AI, animal intelligence, corvids, and cephalopods.

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