Interstellar object 3I/ATLAS photographed near Mars

A rare interstellar object known as 3I/ATLAS passed near Mars in early October and was photographed by spacecraft at the Red Planet, providing new data on a visitor that has puzzled astronomers since its discovery in July. Images captured by NASA’s Perseverance rover and by the European Space Agency’s ExoMars Trace Gas Orbiter showed a faint, moving source against the background stars as the object made its closest recorded approach to Mars on October 3 and 4.

The ExoMars orbiter’s CaSSIS camera detected 3I/ATLAS as a tiny, fuzzy white dot when the object was about 18.64 million miles from Mars, the ESA said, noting the observation was difficult because the comet is roughly 10,000 to 100,000 times fainter than the instrument’s normal targets. NASA released two Perseverance Navcam images that show a single streak of light; some researchers have suggested the streak results from the object’s motion combined with stacked or long-exposure frames rather than indicating an elongated physical shape.

3I/ATLAS is the third confirmed interstellar visitor observed in the solar system, following 1I/ʻOumuamua and 2I/Borisov. It is moving at roughly 61 kilometers per second, or about 137,000...