China's Tianwen-1 captures interstellar comet 3I/ATLAS near Mars
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China's Tianwen-1 orbiter photographed interstellar comet 3I/ATLAS from about 30 million km away as it passed near Mars, the China National Space Agency said. The images show the comet's tail and glowing coma, confirming it contains volatile materials that began escaping as it warmed.
The Observation
Tianwen-1, orbiting Mars for four years and eight months, used its High-Resolution Imaging Camera (HiRIC) to capture the comet on July 24, 2026. The team prepared for the encounter since early September, conducting simulations and instrument inspections. The comet, 5.6 km in diameter, was moving at 58 km/s relative to the Sun and 86 km/s relative to Tianwen-1.
Technical Challenges
HiRIC was designed for bright Martian surface features, not dim objects like 3I/ATLAS. The comet appeared 10,000 to 100,000 times fainter than sunlit Mars. Despite these challenges, the camera captured a visible tail and coma, supporting the comet's classification.
European Contributions
On October 3, Mars Express and ExoMars TGO also photographed 3I/ATLAS using HRSC and CaSSIS instruments. The comet was exceptionally faint for these sensors. The combined observations provide data on the comet's composition and trajectory.
What's Next
Tianwen-2 is expected to visit a near-Earth asteroid and later study a comet, building on techniques tested with 3I/ATLAS. It remains unclear whether future interstellar objects will be detected in time for similar coordinated observations.
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China's Tianwen-1 captures interstellar comet 3I/ATLAS near Mars
