A European Mars probe witnessed the interstellar comet 3I/ATLAS' Red Planet flyby last week.

On Oct. 3, 3I/ATLAS zoomed within 19 million miles (30 million kilometers) of Mars. The European Space Agency's (ESA) ExoMars Trace Gas Orbiter (TGO) was ready for the closeup, snapping imagery of the interloper using its Colour and Stereo Surface Imaging System (CaSSIS).

"This was a very challenging observation for the instrument," CaSSIS Principal Investigator Nick Thomas said in a statement released by ESA on Tuesday (Oct. 7). "The comet is around 10,000 to 100,000 times fainter than our usual target."

Comet 3I/ATLAS was discovered this past July by the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Río Hurtado, Chile. The "3I" in its name indicates that it's just the thir

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