NASA has released remarkable images of interstellar comet 3I/ATLAS, taken during its close approach to Mars in October 2023. This event is significant as it marks one of the rare occurrences of an interstellar object passing through our Solar System. The comet flew within approximately 30 million kilometres of the Red Planet, enabling multiple missions to capture unprecedented observations.
The Mars Reconnaissance Orbiter (MRO), the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, and NASA’s Perseverance rover all contributed to this scientific milestone. While the European Space Agency and China’s Tianwen-1 orbiter released their data earlier, NASA’s findings were delayed due to a government shutdown. With operations back to normal, researchers now have access to a wealth of optical, ultraviolet, and surface-based observations of the comet.
Unprecedented Observations from Multiple Platforms
MRO’s HiRISE camera, typically employed for studying Martian terrain, was repositioned to capture images of the comet on October 2. The resulting photographs reveal a glowing white streak surrounded by a halo of dust and gas, measuring approximately 1,500 kilometres across. These images represent some of the closest views obtained of any interstellar object, allowing scientists to estimate the size and composition of the comet’s icy nucleus.
MAVEN’s Imaging Ultraviolet Spectrograph (IUVS) performed observations of 3I/ATLAS from September 27 to October 7, producing detailed ultraviolet images. The data unveiled the chemical composition of the coma—the cloud of gas and dust enveloping the nucleus—and provided upper limits on the hydrogen-to-deuterium ratios. Such measurements are crucial for determining the comet’s origins, offering insights into whether it formed in a distant star system with conditions analogous to our own.
Shannon Curry, MAVEN’s principal investigator at the University of Colorado Boulder, described the detections as “significant,” indicating that initial analyses have only begun to uncover the potential insights the data may reveal.
From the Martian surface, the Perseverance rover captured faint images of 3I/ATLAS using its Mastcam-Z instrument on October 4. Due to the comet’s dimness, long exposure times were necessary, resulting in streaked star patterns in the background while the comet appeared as a faint dot. Despite these challenges, this observation marked the first time an interstellar object has been imaged from the surface of Mars.
Insights into the Comet’s Behavior and Future Approaches
Since re-emerging from behind the Sun, 3I/ATLAS has exhibited new behaviours, including increased brightness and enhanced ultraviolet and X-ray activity. The comet’s changing characteristics indicate dynamic processes at play as it continues its journey through the Solar System.
Shane Byrne, principal investigator for HiRISE at the University of Arizona, highlighted 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 is expected to make its closest approach to Earth on December 19, 2025, at a distance of two astronomical units—nearly twice the span between Earth and the Sun. Although it poses no threat, the comet presents a unique opportunity for scientists to study material from beyond our Solar System.
The release of these images signifies a major advancement in the field of interstellar research for NASA and its partners. Each observation contributes to a broader understanding of how interstellar objects form, evolve, and navigate through galaxies, potentially unveiling secrets about the origins of planetary systems.
