An Interstellar Target of Opportunity: Lessons Learned from the 3I/ATLAS Spacecraft Campaign

The detection of Interstellar Objects (ISOs) passing through the solar system allows for the direct examination of material from other star systems. The ISO 3I/ATLAS, discovered July 1, 2025, with an incoming velocity at infinity of 57.9778 km/s,  was rapidly recognized to in a retrograde but low-inclination orbit that would take it within the orbit of Mars, relatively close to many of the interplanetary spacecraft in and traversing the inner solar system. This orbit, and the discovery of 3I/ATLAS out near the orbit of Jupiter, enabled an unprecedented spacecraft observing campaign, with at least 25 spacecraft observing 3I/ATLAS during its passage through the solar system. Observations in IR, visual, UV and X-ray wavelengths, were obtained from 11 interplanetary spacecraft,
8 solar probes and observatories, and 6  space telescopes. Of these, the Psyche spacecraft observed 3I/ATLAS on Sep. 8 and Oct. 29, 2025, the Lucy spacecraft from Sep. 15-17, 5 spacecraft on or orbiting Mars observed from Sep. 27 to Oct. 7, the Europa Clipper observed in Nov. and the Juice spacecraft from Nov. 2 - Nov. 25, with observations from the Juno spacecraft orbiting Jupiter finishing this campaign with observations in  March of 2026. The PUNCH, STEREO, SOHO, and GOES-19 solar observatories also provided near continuous monitoring of the integrated visual brightness of 3I/ATLAS for the period Sep. 12 - Nov. 13, 2025, when observations from Earth were difficult or impossible. The spacecraft data acquired in these 7 months will undoubtedly revolutionize the study of ISOs. In this talk, we will review these results, and examine how future ISO observing campaigns should be conducted,  and what sort of ISO interceptor missions will be possible. Planning needs to begin now to prepare for future such observing campaigns for not-yet-discovered ISOs, and space agencies need to consider setting up means to fund this work.