Juice Mission Captures Rare Comet 3I/ATLAS Encounter in Deep Space

The European Space Agency’s Jupiter Icy Moons Explorer (Juice) spacecraft achieved a rare feat in late 2025 and early 2026: observing the interstellar comet 3I/ATLAS. Discovered in July 2025 by an asteroid alert telescope in Chile, 3I/ATLAS is only the third interstellar object confirmed to have passed through our solar system. What makes this encounter particularly noteworthy is the speed with which the observation campaign was assembled – just four months – and the unique vantage point Juice provided, different from any Earth-based observation.

An Unexpected Visitor and a Race Against Time

Interstellar objects, originating outside our solar system, are incredibly difficult to predict, and study. When 3I/ATLAS was identified, scientists quickly worked to determine its trajectory. Marco Fenucci, a Mathematician and Near-Earth Objects Dynamicist at ESA’s Near-Earth Object Coordination Centre (NEOCC), realized Juice was uniquely positioned to observe the comet. “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,” he explained.

Juice was predicted to be closest to 3I/ATLAS after the comet reached perihelion – its closest approach to the Sun – in November 2025. Normally, planning for such an observation campaign would take around nine months. However, the fleeting nature of the opportunity demanded a much faster response. Angela Dietz, Juice Spacecraft Operations Manager (SOM), described the compressed timeline: “When ATLAS came, we knew there was not a lot of time.” The team streamlined the process by temporarily bypassing the standard Science Operations Centre (SOC) calibration and data processing step, working directly with instrument teams to accelerate planning.

Navigating Challenges in Deep Space

The path to observing 3I/ATLAS wasn’t without its hurdles. Juice had recently completed a Venus flyby on August 31, 2025, but experienced a communication failure days before the maneuver. This required intensive troubleshooting, ultimately resolved before the flyby, ensuring the spacecraft remained on course for the comet encounter.

Following the Venus flyby, Juice entered a “hot-cruise phase,” where its high-gain antenna was pointed towards the Sun to shield it from heat. This configuration limited observation capabilities until after the 3I/ATLAS campaign. By early October 2025, the NEOCC provided final trajectory information, allowing the flight control and flight dynamics teams to finalize observation plans within these thermal constraints.

The Encounter and Data Acquisition

Juice officially began observing 3I/ATLAS on November 2, 2025, continuing through November 25. The closest approach occurred on November 4, at a distance of approximately 0.4 AU (60 million km). This distance, combined with Juice’s suite of instruments – designed for studying Jupiter’s icy moons – proved ideal for analyzing the icy interstellar body. Specifically, the JANUS, MAJIS, UVS, SWI, and PEP instruments were utilized.

Due to thermal limitations, observations were restricted to six 45-minute slots and one final 4-hour slot, generating 126 science files totaling 11.18 Gbits of data. However, the data couldn’t be immediately transmitted back to Earth. Juice remained in its hot configuration, preventing it from reorienting its antenna. The data was stored onboard the spacecraft’s mass memory (SSMM) until Juice transitioned to a “cold-cruise phase” in mid-January 2026, enabling high-bitrate data downlink.

First Glimpse of an Interstellar Traveler

The long-awaited data downlink finally occurred in two 11-hour passes on February 17 and 20, 2026, utilizing the ESTRACK deep space antennas at New Norcia and Malargüe. The first pass proceeded smoothly, and the second pass, on February 20, yielded the first images from Juice’s navigation camera, eliciting excitement from the control room team.

The initial image released by ESA shows filaments of gas and dust trailing behind the comet’s bright coma – the cloud of gas and dust surrounding the nucleus. This is the first time Juice has observed 3I/ATLAS, which is now receding from the solar system. Scientists are currently analyzing the extensive dataset, with initial findings expected to be announced later in March 2026.

Looking Ahead: A Testament to Adaptability

The successful observation of 3I/ATLAS highlights Juice’s ability to adapt to unexpected opportunities. Angela Dietz expressed pride in the team’s accomplishment: “That’s the nice thing in our job – It’s always a team effort of many parties involved. I think, the fact that we could optimise this campaign in little time and maximise the output is something to be proud of!” Federico Giannetto, Juice Spacecraft Operations Engineer, added that the experience has increased confidence in the mission’s ability to quickly respond to scientific objectives, even with limited warning.

As Juice continues its journey towards Jupiter, preparing for Earth flyby in September, the 3I/ATLAS encounter serves as a reminder of the unexpected discoveries that can arise in space exploration. As Dietz noted, “Nobody’s ever done a lunar-Earth flyby or been so close to an interstellar object’s perihelion. These are very rare and remarkable things!”