China’s Tianwen-1 spacecraft photographed the interstellar object 3I/ATLAS as it passed close to Mars. The orbiter used high-resolution cameras to capture the comet from about 30 million kilometers (18.6 million miles) away, the China National Space Administration (CNSA) said.
Tianwen-1 has been in orbit around Mars for four years and eight months, making it one of the closest probes to observe interstellar objects since its discovery (May 7, 2025).
Tenbun-1 reveals comet’s tail and coma
The new image shows several features that support the conclusion that 3I/ATLAS is a comet. A visible tail extends behind the object, and a cloud of gas and dust (the coma) surrounds its core.
The researchers combined multiple images to create an animation that tracks the comet’s movement as it approaches the sun. The observations add to growing evidence that 3I/ATLAS contains water and other volatile materials that begin to escape as the object warms as it passes through the solar system.
The success of this observation also indicates what kind of work China plans to do with Tianwen-2. The mission will visit a near-Earth asteroid (NEA) and then study a comet.
Acquire small, fast-moving targets
The team responsible for Tianwen-1’s High-Resolution Imaging Camera (HiRIC) began preparing for the encounter in early September. Their work includes iterative simulations, theoretical modeling, and detailed inspections of equipment.
Imaging 3I/ATLAS was difficult because the object was far away and relatively small (5.6 km in diameter, 3.5 miles). That speed added an even greater challenge. The comet was moving at about 58 km/s (36 mi/s), but its motion relative to Tenbun-1 reached about 86 km/s (53.5 mi/s).
Also, this camera was not originally designed to observe such dark objects. HiRIC was primarily designed to study bright features on the surface of Mars, similar to instruments aboard the European Space Agency’s Mars Express and ExoMars Trace Gas Orbiter (TGO) spacecraft.
Mars rover points camera at 3I/ATLAS
On October 3, both European spacecraft also imaged 3I/ATLAS. Mars Express used the High Resolution Stereo Camera (HRSC), while the ExoMars spacecraft relied on the Color and Stereo Surface Imaging System (CaSSIS).
This comet was extremely difficult to detect with these instruments. Compared to the sunlit terrain of Mars, 3I/ATLAS appeared approximately 10,000 to 100,000 times dimmer.
The High Resolution Stereo Camera (HRSC) on board Mars Express has a 0.5 second exposure time, while the Color and Stereo Surface Imaging System (CaSSIS) can expose images for 5 seconds. Tianwen-1 collected observations with its High-Resolution Imaging Camera (HiRIC).
Exposure times for the HiRIC are not published, but the camera is designed for precise timing and rapid operation. These features now allow the team to obtain up-to-date images, even if they look grainy and blurry.
A rare sample from another star system
Like two previously identified interstellar objects, 3I/ATLAS offers unusual opportunities for both astronomy and astrobiology. Asteroids and comets preserve material left over from the formation of planetary systems, so objects arriving from interstellar space may contain clues about the conditions around another star.
Studying such visitors could reveal how other planetary systems form and what kinds of materials they contain. Missions aimed at intercepting interstellar objects (for which many concepts are being considered) could allow scientists to gather information not available through regular telescopic observations.
The only comparable alternative would be to send a spacecraft directly to another star, which would require an enormous amount of time and money.
Future missions could track interstellar visitors
Scientists hope that future spacecraft will be able to pick up newly discovered interstellar objects and examine them at close range.
One initiative already in development is the European Space Agency’s comet interceptor. The mission is expected to be completed by 2029, and will wait in space for an opportunity to investigate suitable comets or other promising targets.
