An unexpected visitor

On 1 July 2025, an asteroid alert telescope in Chile confirmed an interstellar object had entered our Solar System. The icy body - 3I/ATLAS - is the latest of only three interstellar objects known to have passed through our solar neighbourhood.

Rare and hard to predict, scientists rushed to determine 3I/ATLAS’s orbital trajectory and see what observation options would be available to them.

“Almost since the time of discovery, we realised that the geometry of the orbit would allow observations from the Juice spacecraft, which would observe the comet from a completely different angle than what we can do from Earth,” says Marco Fenucci, Mathematician and Near-Earth Objects Dynamicist at ESA’s Near-Earth Object Coordination Centre (NEOCC).

Calculations predicted that Juice would be the closest spacecraft to 3I/ATLAS right after the icy object reached perihelion, in November 2025.

“Preparations for things like payload pointing campaigns or flybys are usually in the order of nine months,” explains Juice Spacecraft Operations Manager (SOM) Angela Dietz. “When ATLAS came, we knew there was not a lot of time.”

With only four months to prepare a brand-new observation campaign for a completely uncharacterised interstellar object, there was no time to lose.

“With observations in November, we had to complete the planning by the end of September and uplink the commands by mid-October,” Angela explains. “The mission manager and I agreed to streamline the workflow by temporarily skipping the Science Operations Centre (SOC) step. Normally, SOC supports calibration and data processing, but working directly with the instrument teams allowed us to move faster,” she says.

In the months leading up to the encounter, NEOCC worked closely with the flight dynamics team at the European Space Operations Centre (ESOC) towards producing increasingly refined trajectory solutions. “This was essential to point the Juice instruments to image 3I/ATLAS,” says Marco.