New comet accidentally discovered by space telescope

Launched in 2023, the European Space Agency’s (ESA) Euclid space telescope observes some of the most distant regions of the visible universe for signs of dark matter and dark energy. But even while focused on the “big picture,” Euclid’s onboard equipment is surprising astronomers by capturing tiny photobombers like errant comets.

Its recent portraits of one specific dusty space rock are especially impressive, however. Euclid spotted a never-before-seen comet sailing through space more than 807.7 million miles from Earth. The telescope isn’t designed to automatically flag an image interloper. Instead, the bright blemish seen in multiple images was spotted by a moving object detection program designed by Mikko Pöntinenan astronomer at the University of Helsinki in Finland.

“I was excited to see my software flag a ‘streak’ smeared across several images—the result of a fast-moving object,” said Pöntinen. “Further inspection revealed that it had a fuzzy cloud around it, indicative of an active object like a comet that is shedding dust and gas.”

Comet C/2026 S1 (Euclid) seen in a wide VIS image for context (left), with a zoom in (right). Credit: ESA/Euclid/Euclid Consortium/NASA, M. Pöntinen et al. 2026

Pöntinen quickly relayed his findings to the International Astronomical Union’s Minor Planet Center (MPC), which then passed the news along to researchers around the world. On October 8, the MPC confirmed the newly discovered comet, which is now classified C/2026 S1 (Euclid).

C/2026 S1 was seen from five different fields of view over multiple days in the Euclid Deep Field North region of the telescope’s scans. Astronomers now know the comet’s trajectory isn’t located on the same horizontal plane as the planets. Instead, its path is technically taking it over the solar system along a multi-thousand-year orbit.

Euclid’s discovery is particularly striking because the telescope’s six-year mission is specifically mapped to avoid areas of the sky that are laden with comets and asteroids.

“Very few comets are expected to be discovered by Euclid, so it was a happy coincidence,” added Euclid archive scientist Bruno Altieri.