The interstellar object known as 3I/ATLAS just flew past Mars, and China’s Tianwen-1 mission managed to snap some images with its high-resolution camera. According to the China National Space Agency (CNSA), the orbiter’s high-resolution camera captured images of the comet from a distance of about 30 million kilometers (18.6 million miles). This makes the Tianwen-1 orbiter, which has been orbiting Mars for four years and eight months, one of the closest missions to observe the ISO since its first discovery (on May 7, 2025).
The image shows the comet-like features of 3I/ATLAS, including its tail and the surrounding gas envelope (coma). The images captured by China’s orbiter were also stitched together to create an animation showing its trajectory and path as it approaches its next flyby of the Sun. This is the latest in a long line of evidence that 3I/ATLAS is an interstellar comet composed of water and volatiles that have been outgassing since it began its approach to the Sun. It also offers a glimpse of what China’s Tianwen-2 mission will see in the coming years when it rendezvous with a near-Earth asteroid (NEA) and a comet.
The team managing the orbiter’s High-Resolution Imaging Camera (HiRIC) began preparing for the observation capability in early September. This included conducting repeated simulations, theoretical modeling and extensive instrument testing. The task of imaging 3I/ATLAS was particularly challenging due to its distance and small size (5.6 km, 3.5 miles in diameter), but also the speed at which the ISO and orbiter move. While 3I/ATLAS reaches about 58 km/s (36 mi/s), while the orbiter has a relative speed of 86 km/s (53.5 mi/s).
In addition, the HiRIC camera is designed to study brightly lit structures on the surface of Mars, similar to ESA’s Mars Express and ExoMars Trace Gas Orbiter (TGO) missions. On October 3, these orbiters also captured images of 3I/ATLAS with their cameras – the High Resolution Stereo Camera (HRSC) and the Color and Stereo Surface Imaging System (CaSSIS). In all cases, 3I/ATLAS is about 10,000 to 100,000 times fainter than the surface features of Mars when imaged in daylight.
However, the High Resolution Stereo Camera (HRSC) on the Mars Express and the Color and Stereo Surface Imaging System (CaSSIS) have exposure times of 0.5 seconds and 5 seconds, respectively. In the case of Tianwen-1, the images were captured using its high-resolution imaging camera (HiRIC). Although the exposure time is not publicly disclosed, the camera was designed for high timing accuracy and fast responses, which allowed the science team to capture this latest (albeit grainy and blurry) ISO image.
Like its predecessors, 3I/ATLAS is a particularly interesting object because of the opportunities it offers for astronomical and astrobiological research. Because asteroids and comets are essentially leftovers from the formation of solar systems, studying these objects could allow scientists to learn what conditions exist in other star systems. Essentially, an ISO interception mission (for which numerous concepts are being explored) could provide information that would otherwise be impossible unless sending missions to other stars – an extremely time-consuming and expensive approach.
In the coming years, scientists hope to have a mission operational that could intercept and study future ISOs up close. This also includes ESA’s Comet Interceptor, which is expected to be completed by 2029.
Further reading: CGTN
Comments are closed.