Euclid space telescope discovers first comet in surprise find

ESA's dark energy mission spots long-period comet C/2026 S1 (Euclid) in deep field survey

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Published19 October 2026

Updated19 October 2026

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The European Space Agency's Euclid space telescope, designed to map distant galaxies and probe dark energy, has discovered its first comet, a long-period object designated C/2026 S1 (Euclid), in an unexpected find during routine observations between September 16 and 24, 2026.

Euclid, launched in July 2023, is primarily tasked with observing about 1.5 billion galaxies to measure their redshift and shed light on the expansion history of the universe and the nature of dark energy. To avoid interference from dust, the telescope deliberately avoids observing along the plane of the Milky Way, where most asteroids and comets are found.

The comet was detected by new software developed by Mikko Pöntinen of the University of Helsinki, working with the Solar System Objects Science Working Group of the Euclid Consortium. The software flagged a streak across several images — the signature of a fast-moving object.

"I was excited to see my software flag a 'streak' smeared across several images — the result of a fast-moving object," Pöntinen said in an ESA press release. "By predicting its position I could identify it in other images, in total finding it in five image sets. 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."

The object was compared with known comets and asteroids, and no match was found. Pöntinen reported the discovery to the Minor Planet Center, which confirmed the comet through ground-based follow-up observations and assigned the name C/2026 S1 (Euclid).

The comet is located about 1.3 billion kilometers from Earth, roughly halfway between the orbits of Jupiter and Saturn. It is a long-period comet, taking thousands of years to complete one orbit. Its unusual orbit arches above the galactic plane, bringing it into one of Euclid's fields of view — the Euclid Deep Field North in the constellation Draco, a region chosen because it overlaps with a deep field previously surveyed by NASA's Spitzer Space Telescope.

Euclid observed the comet across five sub-fields with a total of 16 exposures.

"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.

Valeria Pettorino, Euclid Project Scientist, added that while the comet is not a suitable target for ESA's future Comet Interceptor mission, the discovery process provides a real test case for coordination between the two mission teams. "We are of course happy to have discovered a previously unknown comet for the Solar System community to follow-up on," she said.

Analysis

Why This Matters

Euclid's first comet discovery demonstrates that a telescope built for cosmology can also contribute to solar system science through serendipitous detections.
The find validates new software designed to identify moving objects in Euclid's deep-field images, which may lead to more discoveries despite the telescope's deliberate avoidance of the Milky Way plane.
The rapid confirmation and designation process provides a practical test for future coordination between Euclid and the upcoming Comet Interceptor mission.

Background

Euclid is a European Space Agency telescope launched in July 2023 with the primary mission of surveying billions of galaxies to understand the expansion of the universe and the role of dark energy. It operates from the Sun-Earth L2 Lagrange point and conducts both wide and deep surveys. To achieve its deep-sky goals, Euclid avoids pointing near the Milky Way's plane, where interstellar dust complicates imaging. The discovery of C/2026 S1 (Euclid) was an unexpected bonus, made possible by the comet's unusual orbit that takes it high above the galactic plane.

Key Perspectives

Euclid Science Team: The discovery team, including Mikko Pöntinen, Bruno Altieri, and Valeria Pettorino, expressed excitement at the find and noted its value as a proof-of-concept for detecting solar system objects with the telescope. Solar System Astronomers: The Minor Planet Center and ground-based observers now have a new long-period comet to track and study, offering insights into pristine material from the early solar system. Comet Interceptor Mission: While this particular comet is not a viable target, the collaborative process between the Euclid and Comet Interceptor teams has been rehearsed and refined.

What to Watch

Continued ground-based observations of C/2026 S1 (Euclid) to refine its orbit and characterize its composition.
Whether Euclid's software detects additional comets or asteroids in its deep-field surveys over the coming years.
Future coordination between Euclid and the Comet Interceptor mission, which may benefit from the systems tested here.

Sources

The ESA's Euclid Space Telescope Has Discovered A New Comet · Universe Today
Euclid discovers new comet · ESA Space Science

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11 claims in this story checked against 2 sources: 9 supported.

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SupportedHeadline and summary: Euclid has discovered its first comet, and it was a surprise find.Universe Today: “The space telescope has observed other comets, but this is the first time it's discovered one.”
SupportedThe comet was found in images taken between 16 and 24 September 2026.ESA Space Science: “in images taken between 16 and 24 September 2026”
Partly supportedThe discovery happened during 'routine observations'.Universe Today: “The discovery relied on new software designed by Mikko Pöntinen”
Reports differEuclid deliberately avoids the Milky Way plane, where most asteroids and comets are found, to avoid dust.ESA Space Science: “Euclid deliberately avoids the asteroid- and comet-rich band of sky along the Solar System’s plane to reduce unwanted glare from dust”
SupportedPöntinen's software flagged a streak across several images, the signature of a fast-moving object, and he said so in an ESA press release.ESA Space Science: “I was excited to see my software flag a ‘streak’ smeared across several images – the result of a fast-moving object. By predicting its position I could identify it in other images, in total finding it in five image sets”
SupportedPöntinen, of the University of Helsinki, made the discovery with the Solar System Objects Science Working Group of the Euclid Consortium.ESA Space Science: “Mikko Pöntinen of the University of Helsinki [ 3 ], together with the Solar System Objects Science Working Group of the Euclid Consortium, made the initial discovery”
SupportedGround-based follow-up observations helped the Minor Planet Center confirm the comet and name it C/2026 S1 (Euclid).Universe Today: “Ground-based follow-up observations helped confirm the comet, and the MPC gave it the name C/2026 S1 (Euclid), following convention.”
SupportedThe comet is about 1.3 billion kilometres from Earth, roughly halfway between the orbits of Jupiter and Saturn.ESA Space Science: “The comet is located approximately 1.3 billion kilometres away from Earth, equivalent to the distance from the Sun to roughly between the orbits of Jupiter and Saturn.”
SupportedEuclid observed the comet across five sub-fields with a total of 16 exposures.ESA Space Science: “in five image sets [ 4 ]”
SupportedAltieri said very few comets are expected to be discovered by Euclid, and the find was a happy coincidence.ESA Space Science: ““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,””
SupportedPettorino said the comet is not a suitable target for Comet Interceptor, and that she was happy to have discovered a previously unknown comet for follow-up.Universe Today: “We are of course happy to have discovered a previously unknown comet for the Solar System community to follow-up on,” added Valeria Pettorino, Euclid Project Scientist.”