ESA says the find is impressive: Euclid is meant to image distant galaxies, not fast-moving tiny objects.
ESA announced Euclid’s first comet discovery, noting that Euclid is meant to take deep, steady images of distant galaxies, not fast-moving tiny objects.
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ESA's Euclid space telescope has found its first previously unknown comet in images captured from September 16 to 24, 2026. The object, now designated C/2026 S1 (Euclid), appeared while the spacecraft was doing work far outside the usual job description for a mission built to map distant galaxies.
That mismatch is what made the discovery notable. Euclid normally takes deep, steady views for precision galaxy mapping, not repeated observations of Solar System objects moving across the sky. The European Space Agency's account of the discovery says the telescope had detected previously known comets, but this was its first new one.
Mikko Pöntinen, a University of Helsinki doctoral student working with the Euclid Consortium's Solar System Objects Science Working Group, made the initial discovery with moving-object detection software he developed. The program flagged a streak smeared across several images. By predicting where the object should appear, Pöntinen found it in five fields of view collected over several days, totaling 16 exposures.
Closer inspection showed a fuzzy cloud around the object, a sign of an active comet shedding dust and gas. Catalogue checks found no match among known comets or asteroids, so the team reported the observations to the International Astronomical Union's Minor Planet Center. Ground-based astronomers then contributed follow-up observations, and the center confirmed it as a comet on October 8.
ESA placed the comet approximately 1.3 billion kilometers from Earth when it reported the discovery. For scale, the agency compared that distance with the distance from the Sun to a point roughly between the orbits of Jupiter and Saturn. The comet follows a highly inclined path above the planets' usual plane and will take thousands of years to complete its orbit.
Euclid deliberately avoids the asteroid- and comet-rich band along the Solar System's plane because dust there can interfere with sensitive deep-sky imaging. Its step-and-stare survey also normally visits each patch of sky only once, making a moving object difficult to revisit on demand. ESA said the comet happened to cross multiple fields as Euclid scanned, and that the mission is expected to discover very few comets.
Even so, identifying moving objects helps researchers remove trails and extra light from observations intended for galaxy mapping. C/2026 S1 is not a suitable target for ESA's planned Comet Interceptor mission, but Euclid project scientist Valeria Pettorino said its discovery and alert process provides a test case for how the two mission teams could coordinate in the future.
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@esascience. @ESA_Euclid discovers its first comet ☄️ That's quite impressive for a #DarkUniverse detective 🕵️ meant to take deep, steady images of distant galaxies, not fast-moving tiny objects. Discover more about the comet 👉 https://www.esa.int/Science_Exploration/Space_Science/Euclid/Euclid_discovers_new_comet
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