
The comet, known as Siding Spring (C/2013 A1), made its closest encounter with Mars on Sunday at 2:27 pm (1827 GMT), racing past the Red Planet at a breakneck 126,000 miles (203,000 kilometers) per hour.
At its closest, Siding Spring was 87,000 miles (139,500 kilometers) from Mars-- about a third the distance between Earth and our moon.
Before the comet passed, it could be seen in space racing toward the brightly illuminated Red Planet, trailed by a cloud of debris.
Scientists said the comet's passing offered a unique chance to study its impact on Mars's atmosphere.
"What could be more exciting than to have a whopper of an external influence like a comet, just so we can see how atmospheres do respond?" asked Nick Schneider, the remote sensing team leader from NASA's MAVEN mission to Mars.
"It's a great learning opportunity."