China’s Tianwen-1 Mars orbiter captured the interstellar comet 3I/ATLAS from 30 million kilometers away on October 3, 2025, marking the first deep-space imaging of an astronomical object by the mission and offering new insights into the comet’s structure and origins.
China’s Tianwen-1 Mars orbiter successfully imaged the interstellar comet 3I/ATLAS on October 3, 2025, from a distance of approximately 30 million kilometers (18.6 million miles). The high-resolution camera aboard the spacecraft, HiRIC, captured the comet’s nucleus and surrounding coma, revealing features like its tail and gaseous envelope. This observation, described by the China National Space Agency (CNSA) as the first imaging of this object from a vantage point significantly out of its orbital plane,
provided critical data on the comet’s dust dynamics and composition, according to a study published in The Astrophysical Journal Letters.
A Challenging Observation
Imaging 3I/ATLAS posed significant technical hurdles. The comet, which measures 5.6 kilometers (3.5 miles) in diameter, moved at 58 kilometers per second (36 miles per second) relative to the Sun, while Tianwen-1’s relative speed reached 86 kilometers per second (53.5 miles per second). The object’s faintness—10,000 to 100,000 times dimmer than Mars’ surface features—required precise timing and adjustments. The HiRIC camera, designed primarily for surface imaging, was repurposed for this task, with exposure strategies tailored to capture the comet’s fleeting presence. The CNSA stated.
European Space Agency (ESA) orbiters, including Mars Express and ExoMars’ Trace Gas Orbiter (TGO), also attempted to observe 3I/ATLAS but faced similar challenges. Mars Express’s High-Resolution Stereo Camera (HRSC) and TGO’s Colour and Stereo Surface Imaging System (CaSSIS) struggled to detect the comet due to its extreme faintness. In all cases, 3I/ATLAS is roughly 10,000 to 100,000 times fainter than Mars’ surface features when imaged in daylight,
a source noted.
Scientific Significance and New Discoveries
3I/ATLAS, the third interstellar object confirmed in our solar system after ‘Oumuamua (2017) and 2I/Borisov (2019), is believed to have originated near the Milky Way’s center, with an estimated age of 3 to 11 billion years. Its trajectory confirmed its interstellar origin, and the Tianwen-1 images provided unique insights into its dust composition. Researchers found that the comet’s coma contained unusually large dust particles, some as big as sand grains.
This is China’s first deep-space observation of an astronomical object,
said CNSA, highlighting the mission’s technical success. The comet’s coma, which spans several thousand kilometers, showed a brightness profile that aligned with models of dust streaming away under solar radiation.
Implications for Future Missions
Internationally, the observation underscores the value of repurposing existing spacecraft for unexpected scientific opportunities.
Unanswered Questions and Global Collaboration
Despite the success, questions remain about 3I/ATLAS’s origins and composition. The CNSA’s data, combined with observations from NASA’s Webb Space Telescope, which detected an unusual CO₂-to-water ratio in the comet, highlights the need for continued international collaboration.
As 3I/ATLAS continues its journey, its trajectory and behavior will be monitored by space agencies worldwide. The Tianwen-1 images demonstrate the potential of repurposed spacecraft to expand our understanding of interstellar objects. For now, the mission stands as a testament to China’s growing role in planetary science and the enduring mystery of objects that travel through our solar system from distant stars.
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