When the interstellar comet 3I/ATLAS traversed the space between the European Space Agency’s Jupiter Icy Moons Explorer (Juice) probe and NASA’s Europa Clipper spacecraft in November 2025, celestial investigators seized an unparalleled opportunity: one probe captured the comet’s illuminated solar-facing side, while the other observed its particulate-laden dark side, concurrently.
In November 2025, 3I/ATLAS passed between ESA’s Juice spacecraft and NASA’s Europa Clipper spacecraft. Image credit: NASA / ESA / Southwest Research Institute.
“As the comet navigated the region between Juice and Europa Clipper, we were afforded the chance to orchestrate observational efforts between the two probes in an informal capacity,” stated Dr. Kurt Retherford, a planetary researcher affiliated with the Southwest Research Institute.
“Critically, our instruments registered emissions of hydrogen, oxygen, and carbon.”
“These atomic species are generated when volatile materials expelled from the comet’s nucleus undergo dissociation into individual atoms upon exposure to solar radiation.”
These distinctive observations were facilitated by the Ultraviolet Spectrograph (UVS) instruments housed within both the Juice and Europa Clipper spacecraft.
“Documenting the interstellar comet presented a particularly engaging supplementary scientific pursuit,” remarked Dr. Philippa Molyneux, also a researcher at the Southwest Research Institute.
“The resultant, exceptionally rare, and singular dataset encompasses gaseous effusions and dispersed particulate matter.”
“This marks the inaugural instance where we have achieved simultaneous, direct perspectives of a comet’s coma, comprising outflowing gases, from two distinct vantages.”
“The Europa Clipper provided a view of the comet’s nocturnal aspect, characterized by a substantial quantity of scattered dust, whereas Juice primarily imaged luminescent gases on its sunlit hemisphere.”
The scientific endeavor revealed elevated concentrations of carbon emissions emanating from 3I/ATLAS, exceeding initial expectations, particularly when contrasted with typical comets originating from our Solar System. This finding lends credence to corroborating evidence from other analyses regarding the interstellar comet’s provenance and material makeup.
An examination of the emission patterns over an extended period elucidated the migratory dynamics of molecular ratios and the comet’s evolutionary trajectory as it journeyed through our celestial neighborhood.
“By scrutinizing the relative abundance of water ice and frozen carbon dioxide, we can establish a comparative analysis of this interstellar comet’s composition against that of comets indigenous to our Solar System,” Dr. Molyneux explained.
“This analytical process assists us in discerning whether the stellar nursery from which 3I/ATLAS originated shares similarities or differences with our own.”
“I consider the collaborative observational planning with Europa Clipper to have been an enjoyable and highly effective demonstration of the synergistic potential between these two distinct missions,” Dr. Retherford commented.
“Moreover, given the involvement of the SwRI team in both exploratory programs, this joint effort represented a particularly noteworthy achievement in our collaborative endeavors.”
