China’s Tianwen-1 probe achieved a remarkable feat by capturing images of the interstellar comet 3I/ATLAS as it passed close to Mars. The record offers scientists a rare glimpse of a celestial body that originated beyond our solar system. The China National Space Agency (CNSA) spacecraft used its high-resolution camera to photograph the comet from a distance of approximately 28.96 million kilometers.
Uncovering a visitor from another star system
Interstellar objects are extremely rare and 3I/ATLAS is only the third ever identified to cross our solar system, after Oumuamua and Borisov. This observation is crucial because these celestial bodies preserve original material from the formation of distant planetary systems, carrying clues about conditions around other stars. Analyzing a visitor like this could reveal details about how other planetary systems formed and what materials they contain, something that cannot be obtained by ground-based telescopes alone.
Technical challenges to capturing the distant comet
The task of photographing 3I/ATLAS required thorough preparation by the Tianwen-1 HiRIC (High-Resolution Imaging Camera) camera team. Starting in September 2025, engineers performed repeated simulations, theoretical modeling, and detailed inspections of the instrument. The comet represented a difficult target, being millions of kilometers away, with a relatively small diameter of 5.6 kilometers and moving at a speed of about 58 km/s. Its speed relative to Tianwen-1 reached approximately 86 km/s, adding to the complexity of the capture.
Furthermore, HiRIC was not initially designed to observe such faint objects. The camera was developed primarily to study bright features on the Martian surface, similar to the instruments aboard the European Space Agency’s Mars Express and ExoMars Trace Gas Orbiter missions. The team’s engineering skills and precision in exposure time were essential in obtaining the images, even though they appear grainy and blurred due to the extreme conditions.
What the 3I/ATLAS images reveal
The new images, captured by Tianwen-1, show features that confirm the nature of 3I/ATLAS as a comet. It is possible to observe a tail that extends behind the object, in addition to a cloud of gas and dust, known as a coma, that surrounds its core. These features, combined in an animation that tracks the comet’s movement toward its closest point to the Sun, add evidence that 3I/ATLAS contains water and other volatile materials. These materials began to escape as the object heated up during its journey through the inner solar system.
Other probes orbiting Mars also observed the comet
On October 3, 2025, during the same period that Tianwen-1 carried out its observations, two other European probes orbiting Mars also photographed 3I/ATLAS. Mars Express used its HRSC (High Resolution Stereo Camera) camera, while the ExoMars Trace Gas Orbiter (TGO) relied on the CaSSIS (Colour and Stereo Surface Imaging System) system.
Detection of the comet by these instruments was exceptionally difficult. Compared to sunlit features on Mars, 3I/ATLAS was between 10,000 and 100,000 times fainter. The differences in camera exposure times — 0.5 seconds for HRSC and 5 seconds for CaSSIS — reflect the technology used to try to capture such an obscure object. The success of these joint observations underscores the importance of international collaboration in space exploration.
Potential for future missions with interstellar objects
The successful observation of 3I/ATLAS by Tianwen-1 serves as a prelude to the kind of work China intends to do with its next mission, Tianwen-2. This mission is planned to visit a near-Earth asteroid and later study a comet.
Scientists hope that future spacecraft will be prepared to intercept newly discovered interstellar objects and examine them up close. One effort in development is the European Space Agency’s Comet Interceptor, expected to be completed by 2029. This mission will wait in space for an opportunity to investigate a suitable comet or other promising target. Such missions represent a viable alternative for obtaining information about other star systems, given the prohibitive time and cost of sending spacecraft directly to other stars.
