Dual Spacecraft Capture Both Hemispheres of Interstellar Comet 3I/ATLAS at Once
Summary
SwRI-led Ultraviolet Spectrograph (UVS) instruments aboard ESA’s JUICE (Jupiter Icy Moons Explorer) and NASA’s Europa Clipper made coordinated observations of interstellar comet ATLAS in November 2025. SwRI leads the UVS instruments on both spacecraft, and as the comet passed between them, researchers informally coordinated to image both hemispheres simultaneously and detect its ultraviolet emissions. The instruments detected hydrogen, oxygen, and carbon emissions — produced as gases escaping the nucleus break apart in sunlight — extending over 5 million kilometers from the nucleus. Europa Clipper captured the night side (scattered dust) while JUICE imaged the day side (glowing gas). Researchers reported elevated carbon emissions relative to typical solar-system comets, which they describe as corroborating 3I/ATLAS’s interstellar origin. Comparing its water-ice and dry-ice ratios to native comets is intended to indicate whether its home system resembles ours.
Key Claims
- SwRI leads the UVS instruments aboard both JUICE and Europa Clipper, enabling simultaneous dual-spacecraft imaging (SwRI).
- This was the first time researchers obtained simultaneous direct views of a comet’s coma from two directions (Kurt Retherford, UVS principal investigator).
- The instruments detected hydrogen, oxygen, and carbon emissions, products of cometary gases photodissociating in sunlight (Retherford).
- Europa Clipper imaged the night side (scattered dust); JUICE imaged the day side (glowing gas), with elements extending ~5 million km from the nucleus (SwRI).
- 3I/ATLAS showed elevated carbon emissions vs. typical solar-system comets, corroborating its interstellar origin (SwRI).
- Water-ice / dry-ice ratios can be compared to native comets to assess whether 3I/ATLAS’s home system resembles ours (SwRI).
Notable Quotes
“We observed hydrogen, oxygen and carbon emissions. These elements are produced when gases escaping the comet’s nucleus break apart when exposed to sunlight.” — Dr. Kurt Retherford, UVS principal investigator
“This was the first time we’ve had simultaneous direct views of a comet’s coma from two directions.” — SwRI research team