The Chinese probe Tianwen-1, currently operating in the orbit of Marte, performed a historic feat for astronomy by capturing the first images of an interstellar comet directly from Planeta Vermelho. The object, called 3I/ATLAS, was documented in October 2025 during its crossing of the inner solar system, establishing a new milestone in the observation of celestial bodies originating from other stellar systems.
The release of images by Administração Espacial Nacional of China (CNSA) not only confirmed the advanced technical capability of the mission, but also transformed Marte into a privileged observatory. The unique perspective, approximately 30 million kilometers from the comet, offers complementary data to ground-based telescopes, allowing a more complete analysis of the rare visitor’s trajectory and composition.
This event represents the third confirmed detection of an interstellar object in our system, following the passes of ‘Oumuamua in 2017 and 2I/Borisov in 2019, and the first to be recorded in such detail by a probe orbiting another planet.
The technology behind the unprecedented record
The feat was accomplished by the Tianwen-1’s high-resolution camera, HiRIC (High-Resolution Imaging Camera), originally designed for detailed mapping of the Martian surface. The mission team repurposed the instrument for a completely different task: tracking a small, faintly glowing, high-speed target in deep space. To ensure success, engineers optimized exposure times, keeping them short enough to avoid blur caused by the comet’s motion, but long enough to capture light from its nucleus and the coma, the cloud of gas and dust surrounding it. The raw images were later processed to create sequences that reveal the object’s displacement against the stellar background, providing crucial visual data for analyzing its orbital dynamics and internal activity. The versatility demonstrated by the HiRIC camera expands the mission’s scientific capabilities beyond its primary objectives.
Details of the unprecedented capture
The operation faced significant challenges, mainly due to the distance of almost 30 million kilometers between the probe and the comet. The commands sent from the Terra took several minutes to reach their destination, requiring the Tianwen-1 to execute the maneuvers autonomously and with millimeter precision so as not to lose the target.
The probe’s thermal stability was also a critical factor in keeping the instruments operating in optimal conditions in the harsh environment of space. The team needed to make extremely fine aiming adjustments to position the HiRIC camera correctly, a task of enormous technical complexity that tested the limits of the spacecraft’s navigation and control systems.
What the photographs reveal about 3I/ATLAS
The photographs released by CNSA clearly display the rocky, icy core of 3I/ATLAS, which appears as a bright spot surrounded by a diffuse cloud of gas and dust, known as a coma. Estimates indicate that the coma extended for thousands of kilometers, a sign of intense cometary activity driven by solar heat.
The comet’s nucleus measures approximately 5.6 kilometers in diameter, a remarkable size for an interstellar object. Sua speed was calculated at an impressive 58 kilometers per second compared to Sol.
During observations, its tail reached a length of about 56,000 kilometers. Análises complementary spectrometric measurements suggest the presence of water ice, carbon dioxide and traces of carbon monoxide.
These compounds indicate that the comet formed in a very cold region of its home star system. The core’s red glow is attributed to complex organic compounds radiated during its long journey through interstellar space.
A global scientific effort in Marte
The 3I/ATLAS observation was not an isolated initiative, with the collaboration of several international missions in Marte. Sondas from Agência Espacial Europeia (ESA), like Mars Express and ExoMars Trace Gas Orbiter, also collected data, providing multiple geometric perspectives of the comet.
NASA contributed Mars Reconnaissance Orbiter (MRO) and its high-resolution camera, while surface rovers like Perseverance were programmed to attempt to photograph the object from the Martian soil.
The Hope probe, from the Emirados Árabes Unidos, and NASA’s MAVEN mission, focused their instruments on analyzing the gaseous composition of the comet’s coma, seeking to understand the materials that were being released by the nucleus.
The complex logistics of interplanetary observation
The photographs were compiled into an animation that illustrates the comet’s movement, providing essential data for calculating its non-gravitational acceleration. Este phenomenon, generated by the sublimation of ices that expel jets of gas and dust, causes deviations in the orbit that cannot be explained by gravity alone. Analyzing these deviations reveals crucial information about the internal activity and composition of the celestial body.
This joint effort was instrumental in refining estimates of the comet’s rotation and modeling the non-gravitational forces that affect its trajectory, creating a complete three-dimensional profile of the visitor. The synergy between the different space agencies demonstrated the importance of international cooperation for the advancement of scientific knowledge, transforming the spacecraft fleet at Marte into a coordinated interplanetary observatory.
The strategic planning of the Chinese mission
The Tianwen-1 team began planning for the observation of 3I/ATLAS in September 2025, shortly after confirming its extrasolar trajectory. The success of the operation depended on extremely accurate orbital predictions to determine the ideal time windows considering the comet’s speed and low luminosity.
Before the main capture, telemetry tests were performed to ensure secure transmission of image data between Marte and Terra. The strategy of using short and multiple exposures was decisive in maximizing the quality of information obtained from such a distant and faint target, serving as an important test of the probe’s tracking capabilities.
The legacy of mission Tianwen-1
Launched in July 2020, Tianwen-1 reached Marte in February 2021, consolidating a milestone for the Chinese space program. The mission, which included an orbiter, a lander and the Zhurong rover, demonstrated China’s ability to conduct complex operations on another planet. Embora the rover has ended its activities, the orbiter continues its scientific work, now proving its versatility also as a space observatory.
Next steps in exploring small celestial bodies
The experience gained with 3I/ATLAS is crucial for the Tianwen-2 mission, launched in May 2025, which aims to collect samples from an asteroid and study a comet from the main belt, strengthening the role of China in the exploration of Sistema Solar.