\tEnabling & Support<\/p>\n
\t\t\t\t\t\t23\/03\/2026
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No matter how much planning goes into space missions, one must always expect the unexpected. But luck favours the prepared. In July 2025, an unexpected visitor entered our Solar System, interstellar object 3I\/ATLAS. ESA\u2019s Jupiter Icy Moons Explorer \u2013 Juice<\/a> \u2013 happened to be in the right place, with the right equipment, at the right time to see it.\u00a0<\/p>\n This unique vantage point offered a fleeting opportunity. What followed was a race against time.\u00a0<\/p>\n \tAn unexpected visitor<\/p>\n \t\t\t\t\t\t\tESA\u2019s Mars and Jupiter missions observe comet 3I\/ATLAS<\/a><\/p>\n 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.\u00a0<\/p>\n Rare and hard to predict, scientists rushed to determine 3I\/ATLAS\u2019s orbital trajectory and see what observation options would be available to them.\u00a0<\/p>\n \u201cAlmost 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,\u201d says Marco Fenucci, Mathematician and Near-Earth Objects Dynamicist at ESA\u2019s Near-Earth Object Coordination Centre<\/a> (NEOCC).<\/p>\n Calculations predicted that Juice would be the closest spacecraft to 3I\/ATLAS right after the icy object reached perihelion, in November 2025.<\/p>\n \u201cPreparations for things like payload pointing campaigns or flybys are usually in the order of nine months,\u201d explains Juice Spacecraft Operations Manager (SOM) Angela Dietz. \u201cWhen ATLAS came, we knew there was not a lot of time.\u201d<\/p>\n With only four months to prepare a brand-new observation campaign for a completely uncharacterised interstellar object, there was no time to lose.\u00a0<\/p>\n \u201cWith observations in November,\u00a0we had to complete the planning by the\u00a0end\u00a0of\u00a0September\u00a0and uplink the commands by mid-October,\u201d Angela explains. \u201cThe mission manager and I agreed to streamline the workflow by temporarily skipping the Science Operations Centre (SOC) step. Normally, SOC supports calibration and data\u00a0processing, but\u00a0working directly with the instrument teams\u00a0allowed\u00a0us to move faster,\u201d she says.<\/p>\n 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. \u201cThis was essential to point the Juice instruments to image 3I\/ATLAS,\u201d says Marco.\u00a0<\/p>\n \tChallenges in deep space<\/p>\n As 3I\/ATLAS observation plans continued, Juice faced its own challenges.\u00a0<\/p>\n Leading up to Juice\u2019s Venus flyby on 31 August 2025, a\u00a0surprise communication failure<\/a>\u00a0days before the manoeuvre sparked round-the-clock troubleshooting. The anomaly was quickly resolved before the flyby, setting the spacecraft on track to its 3I\/ATLAS encounter.<\/p>\n \u201cBecause of the proximity to the Sun, after the flyby, Juice remained in its hot-cruise phase, with its high-gain antenna still pointed at the Sun to act as a heat shield,\u201d Angela explains.\u00a0This hot cruise phase would extend until after the observation campaign.\u00a0<\/p>\n By early October, NEOCC delivered\u00a0final information on 3I\/ATLAS’s position,\u00a0which gave the Juice\u00a0flight\u00a0control and\u00a0flight\u00a0dynamics\u00a0teams the confidence to finalise their observation plans within the spacecraft\u2019s hot constraints.\u00a0<\/p>\n \tThe encounter<\/p>\n \t\t\t\t\t\t\tJuice\u2019s science instruments<\/a><\/p>\n Juice officially began its 3I\/ATLAS observations on 2 November 2025, continuing through to 25 November. The closest approach was on 4 November at about 0.4 AU (roughly 60 million km). \u00a0<\/p>\n This ideal distance paired well with Juice\u2019s payload. As a mission designed and equipped to study Jupiter\u2019s icy moons, Juice\u2019s scientific instruments were a match made in heaven for the icy interstellar body. Specifically, the spacecraft used five of its instruments \u2013 JANUS, MAJIS, UVS, SWI, and PEP \u2013 to take measurements of 3I\/ATLAS.\u00a0\u00a0<\/p>\n Thermal constraints limited these observations to six 45-minute slots and one final 4-hour slot. Together, these generated 126 science files with a total of 11.18 Gbits of data.\u00a0<\/p>\n But the team would have to wait to see the results.<\/p>\n With Juice still flying in its hot configuration after the observation campaign, the spacecraft could not yet turn back to Earth to transmit the data. Instead, all observations were stored onboard the mass memory (SSMM).\u00a0<\/p>\n Only after the spacecraft entered cold-cruise phase in mid-January 2026 would the high bit rate downlink be possible.<\/p>\n \tData at last<\/p>\n \t\t\t\t\t\t\tFirst glimpse of comet 3I\/ATLAS from Juice science camera<\/a><\/p>\n At last, the long-awaited data downlink took place in two 11-hour passes on 17 and 20 February 2026 via ESTRACK\u2019s New Norcia and Malarg\u00fce deep space antennas respectively.\u00a0<\/p>\n The first pass ran smoothly through the night and into the early hours of the next day.\u00a0\u00a0<\/p>\n The second and final pass took place early on 20 February. Upon acquisition of signal and nominal telemetry readings, the transfer began. As the 16\u2011minute signal delay ended, the navigation\u00a0camera\u00a0images finally reached the control room, triggering instant smiles.\u00a0<\/p>\n The rest of the 11-hour downlink ran as expected. By 19:21\u00a0CET\u00a0the 3I\/ATLAS observation campaign officially ended. But it left a lasting impact on the mission team.<\/p>\n \tWe came. We saw. Now, we venture on.<\/p>\n