The asteroid was detected only a few hours before its flyby, spotted by the automated Catalina Sky Survey. The asteroid has an estimated diameter of 157 to 361 feet (48 to 110 meters), making it much larger than the cosmic object that exploded over Chelyabinsk, Russia, in 2013. February, NASA issued a public statement about a smaller, close-flying asteroid called 2018 CB, which was estimated to be from 50 to 130 feet (15 to 40 m) in diameter.
“Asteroids of this size do not often approach this close to our planet — maybe only once or twice a year,” Paul Chodas, manager of the Center for Near-Earth Object Studies at NASA’s Jet Propulsion Laboratory in California, said in a statement at the time. Sometimes astronomers don’t pick such objects because asteroids are small and dark and therefore very difficult to track. The most common kind of asteroid, called a carbonaceous type, is very dark. This kind of space rock may not reflect enough light for an optical telescope to spot it. NASA’s focus right now for near-Earth objects is on cataloging 90 percent of asteroids that are larger than 460 feet (140 m) wide and that will come to within about 4.65 million miles (7.48 million km) of Earth, or about 20 times the distance from Earth to the moon. In almost exactly 11 years from now, the asteroid 99942 Apophis will pass closer to us than the orbit of many man-made satellites on April 13, 2029.