Euclid Telescope Finds Its First-Ever New Comet 1.3 Billion Km Away

Why is the discovery so surprising?

Euclid deliberately avoids the asteroid- and comet-rich band of sky along the Solar System's plane, because dust there creates glare that would spoil its sensitive deep-sky imaging. On top of that, the telescope's 'step-and-stare' strategy typically visits each patch of sky only once, so a comet can't simply be revisited on demand to double-check its characteristics.

"Very few comets are expected to be discovered by Euclid so it was a happy coincidence that the combination of the comet's orbit and Euclid's scanning over those days captured the object in multiple images," said Bruno Altieri, Euclid Archive Scientist and part of the discovery team.

The odds matter here. A telescope that scans most of the sky exactly once, pointed away from where comets cluster, still caught this object 16 times across five fields. Euclid has detected comets before, but all were already known — C/2026 S1 (Euclid) is the first new one.

What kind of comet is it?

C/2026 S1 (Euclid) doesn't travel in the same flat plane as the planets. Instead, it sits 'straight up' from the Sun's perspective, arcing over the Solar System on an orbit that will take thousands of years to complete. Astronomers will refine the orbital period once more data comes in.

Comets are icy, dusty leftovers from the Solar System's birth about 4.6 billion years ago, mostly originating in the distant Kuiper Belt and Oort Cloud beyond the outer planets. When one swings close to the Sun, its ice turns to gas, producing a glowing fuzzy 'coma' and a long tail. Because Solar System comets have barely changed since they formed, studying them helps scientists understand the raw ingredients and conditions that shaped the planets — including clues about where Earth's water and the building blocks of life may have come from.

What does this mean for future missions?

This particular comet isn't a fit for Comet Interceptor, the planned ESA mission designed to visit a pristine comet. But the discovery-and-alert pipeline has now been tested end to end.

"While this particular comet is not a suitable candidate for Comet Interceptor, the process of discovery and alert gives us a real test case for how our two mission teams will coordinate in the future," said Valeria Pettorino, Euclid Project Scientist. "And we are of course happy to have discovered a previously unknown comet for the Solar System community to follow-up on."

There's also a practical payoff closer to home. Tracking Solar System objects helps Euclid's team identify everything in the field of view and strip out 'noise' — moving comet trails or extra light — that would otherwise contaminate the telescope's primary job: precision galaxy mapping.

What is Euclid anyway?

Euclid is a European mission built and operated by ESA, with contributions from its Member States and NASA. Over six years, it will observe the shapes and motions of billions of galaxies out to 10 billion light-years, aiming to reveal the hidden influence of dark matter and dark energy on the visible Universe.

The Euclid Consortium behind the instruments and data analysis counts more than 2,000 scientists from 300 institutes across 15 European countries, the USA, Canada and Japan. Thales Alenia Space built the satellite and service module as prime contractor, Airbus Defence and Space developed the payload module including the telescope, and NASA supplied the detectors for the Near-Infrared Spectrometer and Photometer, NISP.

One happy coincidence, 16 exposures, and a previously unknown visitor now sits on the books for astronomers worldwide to track.