Plate Nº 93 · recorded October 21, 2026
Space & AstronomyReported finding
Euclid Telescope Finds Comet C/2026 S1 While Mapping Dark Energy
ESA's Euclid dark-energy telescope accidentally discovered comet C/2026 S1 some 800 million miles away — and rehearsed alert procedures for the future Comet Interceptor mission.
By Marcus Bennett4 min read703 words
In brief
- ESA announced on October 19, 2026 that Euclid discovered comet C/2026 S1 about 800 million miles (1.3 billion km) away.
- The Minor Planet Center confirmed the discovery on October 8, 2026.
- Euclid imaged the comet five times between September 16 and 24, 2026, in the Euclid Deep Field North.
- The comet orbits almost perpendicular to the solar system's plane and takes thousands of years to circle the sun.
- ESA says the discovery tested coordination for its future Comet Interceptor mission.
A telescope built to map dark matter and dark energy has discovered a comet roughly 800 million miles (1.3 billion km) from Earth, ESA announced on October 19, 2026. The Minor Planet Center has named the object C/2026 S1 (Euclid), after the space telescope that found it — a first for the mission.
The comet sits somewhere between the orbits of Jupiter and Saturn, but not in the flat disk where the planets, asteroids and most comets travel. Instead, it orbits almost straight up from the sun's perspective, on a steep path tilted out of the solar system's plane. Despite moving fast enough to smear across telescope images, it will need thousands of years to complete a single lap around the sun.
How did a cosmology telescope find a comet?
Euclid's job is to survey more than a third of the sky, mapping how galaxies have evolved over cosmic time in the hope of explaining dark matter — the invisible mass that shapes galaxies — and dark energy, the mysterious force accelerating the universe's expansion. Comet-hunting was never on its schedule.
The discovery came from software, not luck alone. Mikko Pöntinen of the University of Helsinki ran object-detection tools on Euclid's images and spotted something that did not belong. He said:
"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. 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."
That fuzzy cloud matters. It marks the object as an active comet outgassing dust and gas, not an inert asteroid.
When and where was it caught?
Euclid was imaging the Euclid Deep Field North — one of its deep-sky survey zones — when the comet drifted through the frame. The telescope captured it repeatedly between September 16 and 24, 2026, with the animated images taken at 00:41:07, 00:58:53 and 01:16:39 UTC on September 17. The Minor Planet Center confirmed the discovery on October 8, 2026.
In the released images, background galaxies hold steady while the comet streaks past as a band of light — the smear of a moving object during a long exposure.
The geometry explains why Euclid saw it at all. The telescope deliberately points away from the solar system's plane to reduce glare from zodiacal dust, the leftover material from planet and asteroid formation. That off-plane viewing direction happens to match where this steeply inclined comet travels.
Bruno Altieri, Euclid archive scientist and a member of the discovery team, said:
"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."
What does this mean for the Comet Interceptor mission?
ESA is building a future mission called Comet Interceptor. The plan: park a spacecraft in space and wait for a pristine comet arriving from the outer reaches of the sun's realm — an object untouched since the solar system formed, ideally one tilted out of the planetary plane like C/2026 S1 (Euclid).
Researchers now think Euclid could help find that target. This comet itself does not qualify, but the discovery exercised the full alert chain between two mission teams.
Valeria Pettorino, Euclid project scientist, said:
"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. And we are of course happy to have discovered a previously unknown comet for the solar system community to follow-up on."
The finding is a byproduct, not a change to Euclid's core science goals — the telescope continues its dark matter and dark energy survey. Astronomers can now follow up on C/2026 S1 (Euclid) from the ground.
One happy coincidence gave ESA both a new comet and a rehearsal for the next one.
via esa.int (Original)
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News editor covering regulation, policy and their impact on general science news at SciBeat.
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