A telescope built to map distant galaxies has found a new object much closer to home. ESA reported on October 19 that Euclid discovered its first previously unknown comet, now named C/2026 S1 (Euclid).
The discovery shows how software can recover useful Solar System observations from images collected for another purpose. Moving objects can interfere with galaxy measurements, so identifying them also helps Euclid's main survey.
Mikko Pöntinen at the University of Helsinki developed software that flagged a streak across the images. He predicted where the object should appear in other exposures and found it in five image sets taken from September 16 to 24.
A fuzzy cloud around the object suggested comet activity. Checks against catalogs found no known match, prompting a report to the Minor Planet Center. Ground-based astronomers added follow-up observations, and the center confirmed the comet on October 8.
ESA placed it about 1.3 billion kilometers from Earth at the time of its announcement. Its orbit rises well away from the planets' main plane. The orbital period remains subject to refinement as observations accumulate.
Euclid usually observes each section of sky only once and avoids the Solar System's crowded plane. Those choices make repeated views of a new comet unusual.
The discovery process also provides a coordination test for ESA's future Comet Interceptor mission. This particular comet is not a suitable target, ESA says.
Euclid's first new comet emerged from data collected for galaxies.
