China’s Tianwen-1 spacecraft documents comet 3I/ATLAS during close pass to Mars

The Chinese probe Tianwen-1 achieved a significant milestone by recording detailed images of the interstellar comet 3I/ATLAS in October 2025. The feat occurred as the object crossed the vicinity of Marte, making it the first time that a celestial body from outside Sistema Solar has been observed from the orbit of Planeta Vermelho.

Operating successfully in Martian orbit, the Chinese spacecraft captured the comet from an impressive distance of approximately 30 million kilometers. Esta observation contributes crucially to global efforts to analyze the composition and characteristics of interstellar objects, an emerging field of study in astrophysics.

Collaboration between several international space agencies has been fundamental to deepening knowledge about this type of celestial body. 3I/ATLAS is the third object originating outside our confirmed Sistema Solar, following Oumuamua in 2017 and 2I/Borisov in 2019, reinforcing the importance of long-term observation missions.

Technical capacity of capture

Tianwen-1’s HiRIC (High Resolution Imaging Camera) camera, originally designed to map the surface of Marte, was fundamental to the success of this operation. Engenheiros Chinese adapted the equipment to track a faint, fast-moving target in deep space, demonstrating the versatility of the onboard technology.

To optimize the capture, detailed simulations were carried out, adjusting the exposure time to avoid blurring caused by the comet’s high orbital speed. The raw data was transmitted to Terra, where specialized systems at Pequim processed the information, generating 30-second image sequences that reveal the comet’s movement.

Overcoming Obstacles in Observation

The distance of 29 million kilometers between Tianwen-1 and comet 3I/ATLAS represented a considerable logistical challenge for the mission team. Ajustes Extremely precise targeting was required, along with maintaining thermal stability of the camera and instruments to ensure sharp images of the comet’s nucleus and coma. An animation was created from the photographs, illustrating the comet’s movement against the background of stars. Esses records are vital to refining calculations of detected non-gravitational acceleration, which can indicate internal activity and ejection of volatile material from the celestial body.

Features of the comet revealed

The photographs released by Administração Espacial Nacional of China reveal the rocky core of 3I/ATLAS, surrounded by an extensive coma of gas and dust. The diameter of the coma reached several thousand kilometers, an indication of intense cometary activity and sublimation of materials.

The object is approximately 5.6 kilometers wide and moves at a speed of 58 kilometers per second. The Sua tail, initially faint, grew to 56,000 kilometers in the August 2025 observations and was directed opposite to the Sol, a behavior typical of active comets.

Initial spectra collected indicate the presence of water ice and carbon dioxide, with weak signals of carbon monoxide. Essa composition suggests that 3I/ATLAS may have formed in a cold protoplanetary disk, possibly in a region distant from Via Láctea, before being ejected into interstellar space.

Central core: Composto by rock and ice, showing a reddish glow of organic dust, suggesting a carbon-rich formation.

Surrounding coma: Nuvem of gaseous material resulting from the sublimation of ice due to solar heat, forming a temporary atmosphere around the nucleus.

Elongated tail: Partículas ejected by the pressure of solar radiation and stellar wind, visible at specific angles and indicating the direction of movement.

Anomalous acceleration: Desvio of purely gravitational movement, a phenomenon under analysis that could reveal details about the ejection of gas jets.

Detailed planning of Tianwen-1

The Tianwen-1 team began planning the observation in September 2025, based on accurate orbital predictions provided by international collaborations. Complex calculations considered the comet’s speed and low luminosity to define the most appropriate observation windows.

Rigorous telemetry testing was carried out to ensure safe and efficient transmission of captured images. Focusing on short exposures was crucial to maximizing the useful signal from the target, which was a considerable distance of 18 million miles, while ensuring data quality.

This extension of the original Tianwen-1 mission tested the tracking capabilities of faint and distant celestial bodies. The results obtained confirm the effectiveness of detection and tracking protocols for future space missions, expanding the range of possible scientific operations.

The operation provided valuable experience in autonomous navigation and system optimization. The integration of subsystems allowed real-time data processing during the probe’s flight, improving the efficiency of information collection.

Collaborative contribution to science

Agência Espacial Europeia (ESA) probes, such as Mars Express and ExoMars TGO, also recorded 3I/ATLAS in the same period. The European data complements the Chinese information, offering different geometric and spectral perspectives of the comet, enriching the global analysis.

NASA used the Mars Reconnaissance Orbiter (MRO) to capture high-resolution photographs with its HiRISE camera. On October 4, 2025, rovers like the Perseverance attempted to capture images from the Martian surface, although with challenges due to distance and luminosity.

The Hope probe, Emirados Árabes Unidos, and NASA’s MAVEN also collected spectrometric data during the comet’s approach. Esses Collaborative efforts are essential to refine estimates of the axial orientation and non-gravitational forces acting on the comet, providing a multifaceted view of the object.

Mars Express (ESA): Realizou detailed analysis of gaseous emissions in the comet’s coma, identifying chemical components.

MRO (NASA): Forneceu high-resolution images of the comet’s nucleus, allowing the study of its surface morphology.

Perseverance (NASA): Realizou attempts to visually detect the comet directly from the Martian soil, seeking a unique perspective.

Hope (UAE): Monitorou the interaction of the comet with the Martian atmosphere, seeking to understand possible effects on the planetary environment.

Mission trajectory Tianwen-1 in Marte

Launched in July 2020, Tianwen-1 entered orbit of Marte in February 2021, marking a historic moment for Chinese space exploration. The mission included the successful landing of the Zhurong rover in May of the same year, on the vast Utopia Planitia plain, where it began its scientific operations. The rover operated for an Earth year, collecting soil samples and detailed geological images, analyzing the mineral composition and local atmosphere, and providing a deeper understanding of Martian geology and its potential to harbor life. The orbiter continues to map the planet with its HiRIC camera, similar to NASA’s HiRISE, currently focusing on studying polar ice and the distribution of dust on the Martian surface, constantly expanding knowledge about Planeta Vermelho.

New frontiers of Chinese space exploration

The successful observations of comet 3I/ATLAS by Tianwen-1 validate research methods for the next phase of Chinese space exploration, exemplified by the Tianwen-2 mission. Lançada in May 2025, this new probe’s main objective is to collect samples from an asteroid close to Terra and a comet from the main belt, further deepening China’s ability to study smaller bodies from Sistema Solar and their origin.