An asteroid roughly the size of Rome’s Colosseum — between 300 to 650 feet (100 to 200 meters) in length — has been detected by an international team of European astronomers using NASA's James Webb Space Telescope. The object, shown in this artist’s conception, is likely the smallest observed to date by Webb.

The detection was serendipitous — the asteroid was found in calibration images of a different asteroid. The lucky finding suggests Webb can detect many such objects.