A European spacecraft built to map galaxies has discovered a new comet serendipitously, proving it can do more than study dark matter and dark energy in the distant universe.
The Euclid Space Telescope spotted the space snowball, dubbed C/2026 S1 (Euclid) between Sept. 16 and 24, after the renegade had smudged five image sets.
The European Space Agency's mission, launched in 2023, takes long exposures of faraway galaxies, not high-speed photography of zippy objects in our own solar system. But moving-object software, developed by Mikko Pöntinen, a doctoral student at the University of Helsinki, flagged an errant streak. Finding and removing stray signals is crucial for the mission to photograph about one-third of the entire sky in every direction around Earth.
"By predicting [the object's] position, I could identify it in other images," Pöntinen said in a statement. "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."
The results show Euclid, a mission in partnership with NASA, can find new comets early, while they are still fairly far from the sun. That buys astronomers time to watch it activate and change as it approaches, as well as study what it's made of. Tracking a comet over time allows researchers to get a more accurate depiction of its orbit, which tells them how close it will come and how bright it might get.
Right now the comet is about 800 million miles from Earth. If you were to compare that distance to planets in the solar system, it would sit roughly between Jupiter and Saturn.
But this comet is not in the flat plane where the planets orbit. Relative to the sun's position, it's actually overhead, looping up and over the solar system. One full orbit for this object would likely take thousands of years to complete, according to ESA.
That's another reason why spotting C/2026 S1 (Euclid) was so fortuitous. The space telescope looks away from the strip of sky along the solar system's plane, where asteroids and comets are common. Dust in that field of view can cause glare that could otherwise spoil deep-sky images. The comet was found in the direction of the Draco constellation in the far northern sky.
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"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," said Bruno Altieri, who was part of the discovery team, in a statement.
Comets are icy, dusty material left over from when the solar system formed around 4.6 billion years ago. As of the writing of this story, there are over 4,000 known comets. When the International Astronomical Union's Minor Planet Center confirmed the detection of C/2026 S1 (Euclid) on Oct. 8, it became one of 13 found so far this year.
Most comets come from the far-off Kuiper Belt and Oort cloud, which lie past the orbits of the outer planets. The interstellar comet 3I/ATLAS that passed through our solar system in 2025 originated from somewhere else in the Milky Way.
When a comet gets close to the sun, its ice becomes gas, which forms a bright, hazy glow around its head, called a coma, and a millions-of-miles-long tail.
Comets from our own solar system have changed very little since they formed, which makes them sort of like time capsules. Studying them helps scientists learn about the raw materials and conditions that created the planets.
"Comets may have brought water and organic compounds, the building blocks of life, to the early Earth and other parts of the solar system," NASA says.