3I/ATLAS during its October flyby of Mars
NASA released images of interstellar comet 3I/ATLAS during its October flyby of Mars, a rare event that saw the third known interstellar object pass within 30 million kilometres of the Red Planet. NASA

NASA has unveiled images of interstellar comet 3I/ATLAS taken during its close flyby of Mars in October, marking one of the rarest astronomical events in recent history. The comet, only the third interstellar object ever observed in our Solar System, passed within 30 million kilometres of the Red Planet, allowing multiple missions to capture unprecedented views.

A Rare Martian Vantage Point

The Mars Reconnaissance Orbiter (MRO), Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, and the Perseverance rover all recorded images of 3I/ATLAS as it swept past. While the European Space Agency and China's Tianwen‑1 orbiter released their data earlier, NASA's contribution was delayed due to the government shutdown.

With operations restored, scientists now have access to optical, ultraviolet, and surface‑based observations of the comet.

MRO's HiRISE camera, typically used to study Martian terrain, was rotated to capture the comet on 2 October. The resulting images show a glowing white smudge surrounded by a halo of dust and gas, measuring about 1,500 kilometres across. These views are among the closest any spacecraft or Earth‑based telescope is expected to obtain, offering scientists a chance to estimate the size and composition of the comet's icy nucleus.

Unlocking Chemical Clues from Afar

MAVEN's Imaging Ultraviolet Spectrograph (IUVS) observed the comet between 27 September and 7 October, producing detailed ultraviolet images. The data revealed the chemical breakdown of the coma—the cloud of gas and dust surrounding the nucleus—and provided upper limits on hydrogen‑to‑deuterium ratios. These measurements are critical for determining the comet's place of origin, offering clues about whether it formed in a distant star system with conditions similar to our own.

Shannon Curry, MAVEN's principal investigator at the University of Colorado Boulder, described the detections as 'significant' and noted that analysis had only begun to scratch the surface of what the data might reveal.

Perseverance's Contribution

From the Martian surface, NASA's Perseverance rover captured faint images of 3I/ATLAS using its Mastcam‑Z instrument on 4 October. Long exposure times were required due to the comet's dimness, resulting in streaked stars across the background while the comet itself appeared as a faint dot.

Despite the challenges, the rover's perspective provided a unique vantage point, marking the first time an interstellar object has been imaged from the Martian surface.

A Growing Mystery

Since re‑emerging from behind the Sun, 3I/ATLAS has displayed new behaviour, including increased brightness, ultraviolet and X‑ray activity, and a more pronounced colour. These changes suggest dynamic processes within the comet as it continues its journey through the Solar System.

Shane Byrne, principal investigator for HiRISE at the University of Arizona, emphasised the rarity of such observations: 'Interstellar objects are still rare enough that we learn something new on every occasion. We're fortunate that 3I/ATLAS passed this close to Mars.'

Looking Ahead

3I/ATLAS will make its closest approach to Earth on 19 December 2025, at a distance of two astronomical units—nearly twice the span between Earth and the Sun. While posing no threat, the comet offers scientists a rare chance to study material from beyond our Solar System.

For NASA and its partners, the release of these images marks a milestone in interstellar research. Each observation adds to the growing body of knowledge about how such objects form, evolve, and travel across galaxies, potentially unlocking secrets about the origins of planetary systems.

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