Asteroid Florence, a large near-Earth asteroid, will pass safely by Earth on Sept. 1, 2017, at a distance of about 4.4 million miles, (7.0 million kilometers, or about 18 Earth-Moon distances). Florence is among the largest near-Earth asteroids that are several miles in size; measurements from NASA's Spitzer Space Telescope and NEOWISE mission indicate it’s about 2.7 miles (4.4 kilometers) in size.

“While many known asteroids have passed by closer to Earth than Florence will on September 1, all of those were estimated to be smaller,” said Paul Chodas, manager of NASA’s Center for Near-Earth Object Studies (CNEOS) at the agency's Jet Propulsion Laboratory in Pasadena, California. “Florence is the largest asteroid to pass by our planet this close since the NASA program to detect and track near-Earth asteroids began.”