Euclid's first comet turned up in frames taken to map distant galaxies

Euclid Deep Field North is one of the few patches the telescope returns to [4]. The comet appears as a streak in 16 exposures taken between 16 and 24 September 2026, across five fields of view [5].

Euclid's design avoids the dusty plane where comets live, so almost nobody expected it to find one [4]. Catching a comet while it is still far from the Sun gives astronomers time to watch it activate and measure what it releases [3].

Mikko Pöntinen, a PhD student at the University of Helsinki, wrote the moving-object software that flagged the streak [2][5]. He predicted where it would appear in later frames, turning one flag into 16 exposures [5]. "I was excited to see my software flag a 'streak' smeared across several images," he said in an ESA release. Closer inspection showed "a fuzzy cloud around it, indicative of an active object like a comet that is shedding dust and gas" [2][6]. He reported it on 29 September for the Euclid Consortium's Solar System Objects Science Working Group [5].

The Minor Planet Center confirmed the comet on 8 October and published an orbit from 54 observations in circular 2026-T146 [1][5].

Ground observers had been sending in positions. The Canada-France-Hawaii Telescope recorded a tail about 12 arcseconds long on 7 October, and Pöntinen measured the coma at 10 arcseconds across [5]. That is a sliver beside the full Moon's roughly 1,800 [5]. Eight shorter exposures, aligned on the comet's motion, left the core and its dust cloud [5].

An orbit almost upright on the planets

The orbit is inclined about 85 degrees to the plane where the planets travel [5]. The European Space Agency (ESA) describes the comet as currently straight up from the Sun's point of view [5][6]. At about 810 million miles (1.3 billion kilometres), it sits roughly in the gap between the orbits of Jupiter and Saturn [1][6].

That geometry made the find unlikely. Euclid points away from the dusty plane where comets and asteroids are common, to keep glare out of its galaxy images [4].

The telescope also steps to a patch of sky, stares for about an hour and moves on, so most of what it records it records once [4]. Comets usually give themselves away by moving, which a single pass cannot show. The deep fields are the exception, revisited a handful of times a year, and that is why this object landed in several frames [4]. One orbit will take thousands of years; astronomers have not published an exact period [4][5].

One of 13 comets found in 2026

Comets are icy leftovers from the solar system's formation about 4.6 billion years ago. Astronomers know more than 4,000 [3]. The Minor Planet Center's confirmation made this one of 13 found so far in 2026 [3]. Astronomers typically find 40 to 70 new comets a year, most through searches built for the job [4].

A rehearsal for Comet Interceptor

ESA says the comet is not a suitable target for its planned Comet Interceptor [1][5][6]. Valeria Pettorino, Euclid's project scientist, said the discovery and alert process "gives us a real test case for how our two mission teams will coordinate in the future" [6].

Euclid launched in 2023 on a six-year plan to map about one-third of the sky and trace dark matter and dark energy [2][4][7]. Its frames target distant galaxies, but they also carry solar-system objects nobody sought [2][5]. The Minor Planet Center has alerted other observers, so follow-up now belongs to ground telescopes [5].