The interstellar object known as 3I/ATLAS recently made a close pass by Mars, offering a unique opportunity for observation. China’s Tianwen-1 mission, equipped with a high-resolution camera, successfully captured images of the comet from a distance of approximately 30 million kilometers (18.6 million miles). According to the China National Space Agency (CNSA), this achievement marks one of the closest observations of the interstellar object (ISO) since its initial detection on May 7, 2025.
The images reveal 3I/ATLAS’s comet-like features, including its tail and the gaseous envelope, or coma, surrounding it. These images were further processed to create an animation illustrating the comet’s trajectory as it approaches its closest pass to the sun. This observation adds to the growing body of evidence suggesting that 3I/ATLAS is an interstellar comet composed of water and volatiles, which have been outgassing as it nears the sun.
Challenges and Preparations for Observation
The Tianwen-1 team began preparations for this observation opportunity in early September. The process involved running repeated simulations, theoretical modeling, and conducting extensive instrument checks. Capturing images of 3I/ATLAS was particularly challenging due to its distance, small size—measuring 5.6 kilometers (3.5 miles) in diameter—and the high speeds at which both the comet and the orbiter travel. The comet moves at about 58 kilometers per second (36 miles per second), while the orbiter travels at a relative speed of 86 kilometers per second (53.5 miles per second).
The High-Resolution Imaging Camera (HiRIC) aboard Tianwen-1, designed to study brightly lit Martian surface features, played a crucial role in this mission. The camera’s ability to capture high time accuracy and fast responses enabled the team to obtain images of the ISO, despite their grainy and blurry nature.
Comparative Observations by Other Missions
On October 3, other Mars missions, including the European Space Agency’s Mars Express and the ExoMars Trace Gas Orbiter (TGO), also captured images of 3I/ATLAS. These missions utilized their respective High Resolution Stereo Camera (HRSC) and Color and Stereo Surface Imaging System (CaSSIS). Despite the challenges, 3I/ATLAS appeared roughly 10,000 to 100,000 times fainter than Mars’ surface features when imaged in daylight.
The HRSC and CaSSIS cameras have exposure times of 0.5 seconds and 5 seconds, respectively. While the exact exposure time for Tianwen-1’s HiRIC is not publicly disclosed, its design for high time accuracy was instrumental in capturing the comet’s image.
Implications for Future Research
Interstellar objects like 3I/ATLAS offer significant opportunities for astronomical and astrobiological research. These objects, being remnants from the formation of solar systems, provide insights into the conditions present in other star systems. Studying such ISOs could yield information that would otherwise require missions to other stars—a costly and time-consuming endeavor.
The success of Tianwen-1 in capturing images of 3I/ATLAS also sets the stage for China’s upcoming Tianwen-2 mission, which aims to rendezvous with a near-Earth asteroid and a comet in the coming years. This mission will further enhance our understanding of these celestial bodies and their origins.
As scientists continue to explore the cosmos, missions like Tianwen-1 demonstrate the potential for international collaboration and innovation in space exploration. The data gathered from these missions not only enrich our knowledge of the universe but also inspire future generations of astronomers and researchers.
