Tianwen-1 probe captures rare images of interstellar comet 3I/ATLAS 30 million km away
The China National Space Administration (CNSA) released unprecedented images of the interstellar comet 3I/ATLAS, captured by the Tianwen-1 probe in orbit around Mars. The recording occurred on October 3, 2025, when the object was approximately 30 million kilometers from the spacecraft. The operation aimed to document the movement of the comet, which follows a hyperbolic trajectory outside the Solar System.
Tianwen-1, launched in July 2020 and in operation around Mars since February 2021, has tuned its high-resolution camera for this task. Engineers carried out simulations in September to align the speeds: the probe travels at 86 km/s, while the comet advances at 58 km/s. The photos reveal clear cometary features, including a coma of gas and dust thousands of kilometers in diameter.
3I/ATLAS represents the third interstellar object detected in the Solar System, after 1I/ʻOumuamua in 2017 and 2I/Borisov in 2019. Astronomers estimate that it is between 3 and 11 billion years old, possibly older than the Solar System, which is 4.6 billion years old. The initial discovery occurred on July 1, 2025, by the ATLAS telescope in Chile.
Technical preparation for observation
The Tianwen-1 team began preparations in September 2025, with calculationsbased on the trajectory, brightness and size of the comet. Simulations tested the positioning of the HiRIC camera, with a 15.2-inch aperture, to overcome target faintness. Fine adjustments ensured 30-second exposures, capturing multiple perspectives.
Ground processing transformed the sequences into an animation that demonstrates the displacement of 3I/ATLAS through space. This data complements observations from other agencies, such as the European one, expanding analyzes of its chemical composition. The operation highlighted the versatility of the probe, originally focused on Mars.
Comet visual details
The images show the icy core of 3I/ATLAS, estimated to be hundreds of meters to less than a kilometer in diameter. The coma appears as a glowing cloud of gases and dust, activated by solar heating during approach. A short tail extends away from the Sun, with signs of a luminous anti-tail.
Astronomers noted that the comet shone faster than predicted as it approached perihelion on October 29, 2025. This activity suggests a high content of volatiles, such as water, differentiating it from local comets. The photos, processed by CNSA, serve as a basis for initial spectral studies.
Historical trajectory and origins
The comet entered the Solar System in May 2025, confirmed as interstellar by its open orbit. Observations from ground-based telescopes such as the Zwicky Transient Facility in California have tracked its path since July. The closest pass to Mars was 29 million kilometers away, allowing for this unique view.
Experts from the European Space Agency calculate that 3I/ATLAS may have formed near the center of the Milky Way, carrying materials from an ancient era of the universe. Its speed of 58 km/s reflects interstellar gravitational acceleration, without the influence of local stars. These traits position him as a cosmic time capsule.
- Core: Icy and rocky, with a diameter of less than 1 km.
- Coma: Gas cloud of thousands of km, emitting by sublimation.
- Tail: Short and elongated, with active dust emission.
- Anti-tail: Phenomenon opposite to movement, visible at specific angles.
Contributions to future missions
Tianwen-1 expanded its scope beyond Mars by recording 3I/ATLAS, validating techniques for opportunistic observations. The mission has been in orbit for four years and eight months, with data supporting Tianwen-2, launched in May 2025 to sample an asteroid and a comet. International collaborations integrate these records with images from probes such as NASA’s Mars Reconnaissance Orbiter.
Researchers plan analyzes combined with observations from telescopes such as Hubble and Webb, despite delays in data releases. The success reinforces China’s role in interplanetary exploration, with a focus on dynamic objects. The observation took place without interference, thanks to precise adjustments in lighting and orientation.
Cometary structure in focus
The coma of 3I/ATLAS exhibits active gaseous emissions, formed by the vaporization of ices under intense solar radiation. The central nucleus, compact and irregular, releases dust that forms the tail observed in the 30-second sequences. This dynamic differs from solar comets, which show more predictable patterns in their closed elliptical orbits. Initial analyzes indicate a composition rich in organic compounds, potentially preserved from their distant origin. The generated animation reveals subtle variations in brightness, correlated to the object’s rotation. These elements provide clues about formation processes in remote stellar systems, integrating data from multiple space missions for accurate modeling.
Additional notes
European probes recorded 3I/ATLAS simultaneously, capturing additional angles of the passage by Mars.
Speed and orbital dynamics
The comet’s speed of 58 km/s reflects its hyperbolic entry into the Solar System. Orbital calculations confirm the absence of permanent gravitational capture. Perihelion in October 2025 marked the point of greatest observed activity. Tianwen-1 engineers synchronized captures to map minute accelerations. These records support simulations of interstellar trajectories.
