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Euclid finds its first new comet

C/2026 S1 turned up in galaxy-survey images; catalogues confirmed a first for the mission.

By GreenSpacealien Editorial1 min read
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Two exposure panels show a moving object shifting between views while background stars remain in the same positions.
An original GreenSpacealien diagram shows C/2026 S1 shifting across Euclid image sets while background stars stay fixed.GreenSpacealien original diagramView full image

A first comet

Between 16 and 24 September 2026, Euclid imaged C/2026 S1 in the Euclid Deep Field North. The telescope is designed to map distant galaxies; this object became its first previously unknown comet, after earlier detections of comets already known to astronomers.[1]

Reading the streak

Euclid holds background stars fixed during each exposure, so a moving object can cross the frame as a streak. University of Helsinki researcher Mikko Pöntinen built software to search Euclid images for that pattern. The faint cloud around the streak suggested an active comet. The team identified it in multiple image sets and combined those positions with ground-based follow-up observations to establish its motion and orbit.[2]

Detection, then confirmation

The team found no match in known-object catalogues and reported the observations to the International Astronomical Union's Minor Planet Center. The centre confirmed the comet on 8 October; ESA announced it on 19 October. This separates detection from confirmation: repeat positions and an outside catalogue check established that the object was new.[1]

A survey built for galaxies

Euclid's observing plan avoids regions dominated by Milky Way stars, interstellar material and zodiacal light, which can interfere with faint-galaxy measurements. Its wide survey covers more than a third of the sky, while its deep survey repeatedly observes three selected patches. Together, these observations will map galaxy distribution across cosmic history.[3]

Sources & further reading

  1. Euclid discovers new cometEuropean Space AgencyPublished October 19, 2026Accessed November 3, 2026

    Dates, Deep Field North and new-comet confirmation.

  2. Meet Euclid's first comet discovery: C/2026 S1 (Euclid)Euclid ConsortiumPublished October 19, 2026Accessed November 3, 2026

    Describes streak detection and follow-up.

  3. Euclid's wide and deep surveysEuropean Space AgencyPublished February 14, 2024Accessed November 3, 2026

    Describes field selection and survey coverage.

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