The first radar images of asteroid 2004 BL86, which made its closest approach today at 8:19 a.m. PST - a distance of only 745,000 miles (3.1 times the distance from Earth to the moon) - reveal that it even has its own small moon.
The closeness did not take anyone by surprise. Asteroid 2004 BL86 was discovered on Jan. 30, 2004, by the Lincoln Near-Earth Asteroid Research (LINEAR) survey in White Sands, New Mexico and its trajectory is well understood. Monday's flyby was the closest approach the asteroid will make to Earth for at least the next 200 year and is the closest a known asteroid this size will come to Earth until asteroid 1999 AN10 flies past us in 2027.
The 20 individual images used in the movie were generated from data collected at Goldstone on Jan. 26, 2015. They show the primary body is approximately 1,100 feet (325 meters) across and has a small moon approximately 230 feet (70 meters) across. In the near-Earth population, about 16 percent of asteroids that are about 655 feet (200 meters) or larger are a binary (the primary asteroid with a smaller asteroid moon orbiting it) or even triple systems (two moons). The resolution on the radar images is 13 feet (4 meters) per pixel.
Radar is a powerful technique for studying an asteroid's size, shape, rotation state, surface features and surface roughness, and for improving the calculation of asteroid orbits. Radar measurements of asteroid distances and velocities often enable computation of asteroid orbits much further into the future than if radar observations weren't available.
The U.S. has the most robust and productive survey and detection program for discovering near-Earth objects (NEOs) and the U.S. have discovered over 98 percent of the known ones. In 2016, NASA will launch a robotic probe to one of the most potentially hazardous of the known NEOs. The OSIRIS-REx mission to asteroid (101955) Bennu will be a pathfinder for future spacecraft designed to perform reconnaissance on any newly discovered threatening objects.
Source: NASA/JPL
