Euclid Finds Its First New Comet, While Looking for Something Else
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Some of the best discoveries are accidents. In September 2026, the European Space Agency's Euclid telescope was staring deep into space to study dark matter and dark energy when a faint streak crossed its images. That streak turned out to be a comet nobody had seen before, now officially named comet C/2026 S1 (Euclid).
ESA announced the find on 19 October 2026. It is the first previously unknown comet the telescope has discovered.
How the comet was found
Euclid's job is to photograph billions of galaxies across a third of the sky, building a 3D map of the universe. It works by pointing, taking long exposures, then moving to the next patch, a step-and-stare routine.
The comet showed up in images taken between 16 and 24 September 2026, during a survey of a region called Euclid Deep Field North. Because it moved during each long exposure, it appeared as a short streak rather than a point. A close look also showed a fuzzy glow around it, called a coma, which is the cloud of gas and dust that marks an active comet.
The detection came from software written by Mikko Pöntinen, a doctoral student in astronomy at the University of Helsinki, designed to flag moving objects in Euclid data. His program noticed the trail stretching across several frames. When the object did not match any known asteroid or comet, he reported it to the Minor Planet Center, the international clearinghouse for small Solar System bodies.
Ground-based astronomers then followed up, and on 8 October 2026 the Minor Planet Center confirmed it as a new comet.
What makes this comet unusual
- A steeply tilted orbit. Most planets, asteroids and comets travel close to the same flat plane around the Sun. C/2026 S1 (Euclid) moves on a path almost perpendicular to it, passing "above" the Solar System. That is one reason surveys never caught it before.
- Far away. It is about 1.3 billion km from Earth, roughly between the orbits of Jupiter and Saturn. Its reflected light takes about 72 minutes to reach Euclid.
- Faint. It sits in the constellation Draco but is far too dim for backyard telescopes.
- Long period. Early estimates suggest an orbit lasting thousands of years. Astronomers will refine that number as more observations come in.
What does the "C/2026 S1" name mean?
Comet names follow a simple code:
- C/ means a non-periodic comet, one with an orbit longer than 200 years.
- 2026 is the year of discovery.
- S refers to the half-month it was found, here mid-to-late September.
- 1 means it was the first comet designated in that half-month.
- (Euclid) credits the discoverer, in this case the telescope.
Why it matters beyond one comet
The discovery proves that Euclid's enormous image archive can be mined for Solar System science, not just cosmology. That matters for ESA's upcoming Comet Interceptor mission, which plans to wait in space for a pristine comet making its first trip toward the Sun. Finding such targets early is the hardest part.
C/2026 S1 (Euclid) does not meet that mission's requirements, but the method that found it could help spot one that does.
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Frequently asked questions
Who discovered comet C/2026 S1 (Euclid)?
It was found in images from ESA's Euclid space telescope by detection software written by University of Helsinki doctoral student Mikko Pöntinen.
When was the comet confirmed?
The Minor Planet Center confirmed it on 8 October 2026, and ESA announced it on 19 October.
Can I see comet C/2026 S1 (Euclid)?
No. It is far too faint for amateur telescopes.
Why wasn't it found earlier?
Its orbit is tilted almost at right angles to the planets' plane, an area many surveys watch less closely.
Is the comet dangerous to Earth?
Nothing reported suggests any risk. It is between the orbits of Jupiter and Saturn.