Photo by Forsaken Films on Unsplash (illustrative)
On 1 July 2025, a survey telescope in Río Hurtado, Chile, spotted 3I/ATLAS, only the third object ever confirmed to come from outside our solar system. Over the following months NASA, the European Space Agency and Japan's JAXA turned an unusual range of instruments toward it before it made its closest pass to Earth on 19 December 2025.
Key facts
NASA alone pointed more than 15 assets at the comet, including Hubble, Webb, the Perseverance rover on Mars, and spacecraft heading for Jupiter, asteroids and the Sun.
ESA's Mars Express and ExoMars orbiters watched it from about 29 million kilometers away in October 2025, and its Juice probe saw an active comet with clear tails in November.
Webb detected carbon dioxide, water, carbon monoxide, carbonyl sulfide and water ice coming off the comet, which ESA says is likely billions of years old.
The XRISM observatory, led by Japan's JAXA with NASA and ESA, and ESA's XMM-Newton made the first X-ray observations of an interstellar comet.
Why it matters
Interstellar comets carry material that formed around other stars. By sharing observations and reusing spacecraft already flying to Mars, Jupiter, asteroids and the Sun, agencies were able to study this rare visitor from many angles at once.
Worth noting
The comet never came closer to Earth than about 270 million kilometers and posed no danger. Its size is still uncertain, somewhere between a few hundred meters and a few kilometers across.