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Euclid discovers a comet far above the planets’ orbital plane

The Euclid space telescope has found its first previously unknown comet, following a moving streak through repeated images. Ground-based observations confirmed the discovery. The object follows a long orbit far above the planets’ plane, an unusual catch for an observatory designed to map galaxies and study dark matter and dark energy.

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An imagined comet with a diffuse coma and short trail against a dark field of stars and distant galaxies.

A moving streak becomes a discovery

The European Space Agency’s galaxy-mapping telescope Euclid has discovered its first previously unknown comet. Mikko Pöntinen, a doctoral student at the University of Helsinki in Finland, found the moving object with software he developed for examining the observatory’s images. A blurred streak extended across several exposures. Predicting where the object should appear allowed him to locate it in other observations, ultimately identifying five separate image sets.[1], [2]

A diffuse cloud around the object indicated an active comet shedding dust and gas. After checks found no match among known comets and asteroids, the team sent observations to the International Astronomical Union’s Minor Planet Center, which collects small-body observations and confirms discoveries. Ground-based observatories supplied follow-up measurements. The centre confirmed the comet on 8 October and designated it C/2026 S1 (Euclid).[1], [2]

A long orbit above the planets

The comet is about 1.3 billion kilometres from Earth and lies far above the plane in which the planets orbit. Its broad path takes thousands of years around the Sun. Euclid captured it between 16 and 24 September, recording 16 exposures across five fields of view. Further observations are needed to refine the orbital period. The telescope had detected comets before, but those objects were already known.[1]

A rare intersection with the galaxy survey

Euclid deliberately avoids the dust-rich band containing most Solar System asteroids and comets, because that glare interferes with its galaxy survey. It normally photographs a region and moves on, making repeated views of moving objects unusual. This comet’s path happened to intersect the survey pattern several times. Recognising such trails also helps remove unwanted light from measurements intended to investigate dark matter and dark energy. That survey measures the shapes and motions of billions of galaxies, distinguishing nearby moving objects from the distant background.[1], [2]

C/2026 S1 is unsuitable for a visit by Comet Interceptor, the planned mission to examine a long-period comet or a first-time visitor to the inner Solar System. Nevertheless, the discovery and alert process gave the teams a real example on which to test coordination between the two missions.[1], [2]

References

  1. News sourceESAEuclid finds a new comet in its galaxy images↩1↩2↩3↩4↩5
  2. News sourceEl PaísEuclid discovers a new comet↩1↩2↩3↩4
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