Asteroid 3122 Florence, a 4.5 kilometer (2.8 mile) wide near-Earth object, made a close pass to Earth on September 01, 2017, treating researchers with the closest known approach to Earth of an asteroid of this size. Thankfully, unlike recent close brushes with substantially smaller rocks, Florence’s orbit brought it no closer to us than 7 million kilometers (4,350,000 miles), more than eighteen times farther out than the Moon’s orbit.
Detailed radar images of Florence were captured by the Arecibo Observatory in Puerto Rico and the Goldstone Deep Space Communications Complex in California. The asteroid was found to have two small 200-meter (656-foot) moons — only the third known near-Earth asteroid to be a trinary system — with the closer of the pair taking roughly 8 hours to complete an orbit, and the farther one somewhere between 22 and 27 hours.
First spotted in 1980, 3122 Florence was named after Florence Nightingale, the founder of modern nursing. Its 2.35-year orbit caries it from a distance just outside of Earth’s orbit to a point 2.5 times farther out. Due to the differences in the orbital periods of Earth and Florence, its next close pass won’t occur until 2050.