Skip to content
SEARCHIT
Menu
SearchIT
SCIENCE

Euclid finds a new comet in images of distant galaxies

C/2026 S1 lies roughly 1.3 billion kilometres from Earth. A recurring trail in the telescope’s images started a sequence of observations and checks.

2 min readBy NOWPOSSIBLE editorial team
Euclid astronomical field with the trail of comet C/2026 S1 highlighted in an enlarged inset.

IN BRIEF

Images were taken on 16–24 September 2026; the Minor Planet Center confirmed the comet on 8 October; ESA announced it on 19 October.

Euclid’s first comet discovery follows earlier observations of already catalogued objects.

WHY IT MATTERS

A new body joins the objects astronomers can follow over time. The discovery also shows the value of revisiting astronomical images with fresh questions. Nearby and distant phenomena share the same frame, and different ways of analysing it can bring different objects into view.

WHAT IS NOW POSSIBLE

Un oggetto prima assente dai cataloghi consultati è ora identificato come cometa e può essere seguito collegando le nuove osservazioni.An object missing from the checked catalogues is now identified as a comet and can be tracked by linking further observations.

WHAT MADE IT POSSIBLE

Mikko Pöntinen’s software flagged the movement. Euclid measures successive patches of sky, pausing between shifts; comparing the images helps reveal objects changing position against the background.

THE STORY

Checks against comet and asteroid catalogues found no match. Reporting the object to the Minor Planet Center alerted ground-based astronomers, enabling follow-up observations. The Center subsequently confirmed the comet.

That sequence makes the discovery verifiable: other observers can look for the same body and add measurements. Linking separate detections allows its path to be reconstructed, while retaining the uncertainties attached to each observation.

In the cover image, taken on 20 September with a 560.52-second exposure, the comet looks elongated. The streak records its movement while the camera collects light, so its length also depends on how long the exposure lasts.

Around it lies the coma, a halo of gas and dust surrounding the icy nucleus. Released material can scatter light across a region much larger than the solid body. This envelope gives comets their fuzzy appearance.

Cover image: Comet C/2026 S1 (Euclid) observations in context. Credit: ESA/Euclid/Euclid Consortium/NASA, M. Pöntinen et al. 2026. CC BY-SA 3.0 IGO. Documentary image with the original inset and annotations; it may be resized for display, with no changes to its content.

WHAT WE KNOW

Sixteen exposures, five fields of view. Circular MPEC 2026-T146 records the name under which further observations of the same object can be linked. [1][2][3][4][5][6]

WHAT WE DON'T KNOW

The orbit still needs refinement. The available positions describe part of its path, so assigning a precise orbital period would be premature. This comet is not a suitable target for Comet Interceptor.

WHAT HAPPENS NEXT

Additional positions measured over time can refine the orbit. The useful change to watch is a reduction in uncertainty about future positions: that is where each new measurement can show its contribution.

SOURCE TRACE

  1. First unknown comet

    [1]

  2. September; 8/10; 19/10

    [1][2][4]

  3. Pöntinen’s software

    [1]

  4. Successive pointings and measurements

    [6]

  5. 20 September; 560.52 seconds

    [3]

  6. Coma: gas and dust around nucleus

    [5]

  7. 1.3 billion km

    [1]

  8. 16 exposures/5 fields

    [1]

  9. Orbit needs refinement

    [1]

  10. Comet Interceptor excluded

    [1]

  11. No catalogue match

    [1]

  12. The report alerted ground-based astronomers, enabling further observations.

    [1]

SOURCES

  1. Euclid discovers new cometEuropean Space Agency · 2026-10-19 · Class A · OFFICIAL_REPORT · Evidence ownerOpen source
  2. MPECs for 2026Project Pluto · Class D · REGISTRY_INDEX · Registry metadataOpen source
  3. Comet C/2026 S1 (Euclid) observations in contextEuropean Space Agency · 2026-10-19 · Class A · OFFICIAL_REPORT · Evidence ownerOpen source
  4. A composite of eight Euclid VIS exposures of Comet C/2026 S1 (Euclid)European Space Agency · 2026-10-19 · Class A · OFFICIAL_REPORT · Evidence ownerOpen source
  5. Comet FactsNASA Science · Class A · REFERENCE · Scientific contextOpen source
  6. How Euclid scans the skyEuropean Space Agency · 2023-06-08 · Class A · REFERENCE · Scientific contextOpen source
  7. MPEC 2026-T146: COMET C/2026 S1 (Euclid)Minor Planet Center · 2026-10-08T15:40:00Z · Class A · ASTRONOMICAL_CIRCULAR · Formal discovery registrationOpen source

CURRENT EVIDENCE

VALIDATED EVIDENCE

CONFIRMED_ASTRONOMICAL_OBSERVATION

RELATED PROGRESS