Alien visitor or cosmic wanderer? What makes interstellar comet 3I/ATLAS so mysterious

China’s Tianwen 1 Mars orbiter has captured detailed images of the interstellar comet 3I/ATLAS during its close approach to Mars in early October 2025. Released by the China National Space Administration (CNSA), the photographs mark a significant milestone in planetary science — offering a rare glimpse of a celestial body that originated beyond our solar system.

A rare interstellar visitor

Comet 3I/ATLAS is only the third confirmed interstellar object to pass through our solar system, following ‘Oumuamua in 2017 and 2I/Borisov in 2019. Believed to be older than the solar system itself, it offers scientists a unique opportunity to study material from distant star systems and better understand the early formation of planets.

How Tianwen 1 captured the comet

Between 1 and 4 October, Tianwen 1 used its High-Resolution Imaging Camera (HiRIC) to photograph the fast-moving comet from a distance of nearly 29 million kilometres. Tracking a body hurtling through space at around 129,800 mph (58 km/s) posed significant technical challenges.

CNSA reported that the data, received and processed by its ground systems, revealed a clear view of the comet’s bright nucleus surrounded by a vast coma spanning several thousand kilometres.

Deep-space test for China’s exploration programme

The mission was conducted as part of Tianwen 1’s extended operations, serving as a technical test ahead of China’s upcoming Tianwen 2 asteroid-sampling mission. According to CNSA, this experiment demonstrated the spacecraft’s capability to detect and image faint, fast-moving celestial bodies — an essential skill for future deep-space projects.

Global collaboration and scientific curiosity

The encounter drew global attention, with both NASA and the European Space Agency (ESA) also redirecting their Mars-based orbiters and rovers to observe the interstellar comet. Researchers hope that combined data from multiple missions will shed light on 3I/ATLAS’s composition, structure and trajectory.

Puzzling acceleration and strange composition

Scientists have noted unusual behaviour in 3I/ATLAS, including unexpected acceleration and a chemical composition containing only about 4% water by mass. These anomalies have led to speculation about its nature.

Harvard astrophysicist Avi Loeb, known for his bold theories, suggested that while 3I/ATLAS is most likely natural, exploring remote possibilities of artificial origin remains a “scientifically interesting exercise”. Most researchers, however, attribute its peculiarities to natural outgassing processes common in comets.

NASA image delay sparks debate

A temporary US government shutdown has delayed NASA’s release of high-resolution images captured by its Mars Reconnaissance Orbiter, which has three times the resolution of Hubble’s camera. The delay has prompted calls from US lawmakers for transparency, although NASA has reiterated that the comet poses no threat to Earth.

A fleeting cosmic encounter

3I/ATLAS will soon leave the solar system forever, continuing its interstellar journey into deep space. For scientists, this brief encounter represents a rare opportunity to observe an object from another star — and for China’s Tianwen 1, a demonstration of its growing role in humanity’s exploration of the cosmos.