Euclid Space Telescope Finds Its First New Comet, Arching Over the Planets
ESA's Euclid telescope spotted a new comet, C/2026 S1 (Euclid), about 1.3 billion kilometers away. How a galaxy-mapping mission caught it and why it matters.
The European Space Agency’s Euclid space telescope has found a comet nobody had seen before. The object, now named C/2026 S1 (Euclid), showed up in images taken between Sept. 16 and 24, and the International Astronomical Union’s Minor Planet Center confirmed it as a comet on Oct. 8, ESA said.
Euclid had photographed comets before, but all of them were already known. This is the first one it has discovered, and it came from a telescope built to stare at faraway galaxies rather than chase objects moving across the Solar System.
A streak in the deep field
The find began with software. Mikko Pöntinen, a PhD student at the University of Helsinki, wrote a program that scans Euclid’s images for small moving objects. Working with the Euclid Consortium’s Solar System Objects Science Working Group, he saw it flag a smeared streak across several frames, the trace of something moving fast.
By predicting where the object would be next, Pöntinen located it in five image sets taken in the Euclid Deep Field North, for 16 exposures in total. A closer look showed a fuzzy cloud around it, the sign of an active comet giving off dust and gas. Catalogs of known comets and asteroids had no match, so the team reported it to the Minor Planet Center, which alerted observers on the ground who added follow-up observations.
Where the comet is
According to ESA, the comet sits roughly 1.3 billion kilometers from Earth. That is about as far as the stretch between the orbits of Jupiter and Saturn is from the Sun. It does not travel in the flat plane where the planets orbit. Seen from the Sun, it is currently “straight up,” on a looping path that takes thousands of years to complete. Astronomers will refine its orbital period as more data comes in.
Comets are icy, dusty leftovers from the Solar System’s birth about 4.6 billion years ago. Most come from the Kuiper Belt and the Oort Cloud beyond the outer planets. When one swings near the Sun, its ice turns to gas and forms a glowing coma (the fuzzy head) and a tail.
Why it matters
Euclid is a hard place to find comets. It avoids the band of sky along the planets’ plane, where most comets and asteroids are, because dust there adds glare to its deep images. Its “step-and-stare” survey usually visits each patch of sky only once, so the team cannot go back on demand for a second look.
“Very few comets are expected to be discovered by Euclid,” said Bruno Altieri, the mission’s archive scientist and a member of the discovery team. He called the catch a happy coincidence of the comet’s orbit and the telescope’s scanning on those days.
The quick path from detection to confirmation shows Euclid can catch new comets while they are still relatively far from the Sun, ESA said. That could one day supply a target for Comet Interceptor, a future ESA mission. This comet is not a suitable candidate, according to Euclid Project Scientist Valeria Pettorino, but she said the discovery and alert process gives the two teams a real test of how they will work together.
Tracking these objects also helps the main mission. Moving comet trails and stray light are noise in images meant for precise galaxy mapping. Over six years, Euclid is observing the shapes and motions of billions of galaxies as far as 10 billion light-years away to study dark matter and dark energy.
Source: European Space Agency
