On January 26, asteroid 2004 BL86 safely flew right past us, making its closest approach around 11:19 a.m. EST at a distance of about 1.2 million kilometers -- that’s only about three times the distance between us and our moon. And it turns out, the asteroid has its own little moon.
Asteroid 2004 BL86 was discovered back in 2004 by the Lincoln Near-Earth Asteroid Research survey in White Sands, New Mexico. Monday’s flyby is the closest the 325-meter-wide asteroid will come to Earth for the next two centuries at least. Here's an animation of its trajectory. This is the closest a known asteroid this size will approach us until asteroid 1999 AN10 flies by in 2027. In the population of near-Earth objects, about 16 percent of asteroids 200 meters or larger are a binary or even triple system, where the primary asteroid has a smaller asteroid moon or two orbiting it.
Sure enough, astronomers working with the Deep Space Network antenna in Goldstone, California, captured 20 individual radar images of asteroid 2004 BL86, revealing a small moon about 70 meters across, according to a NASA Jet Propulsion Laboratory news release.
"When we get our radar data back the day after the flyby, we will have the first detailed images," Lance Benner of JPL in Pasadena, California, said in statement two weeks ago. "At present, we know almost nothing about the asteroid, so there are bound to be surprises." Well, surprise!
Radar measurements help researchers study the size, shape, rotation state, surface features, and surface roughness of asteroids. They’re also quite useful for improving the calculation of orbits. These 20 new radar images were used to make this movie.
"Asteroids are something special. Not only did asteroids provide Earth with the building blocks of life and much of its water, but in the future, they will become valuable resources for mineral ores and other vital natural resources,” says Don Yeomans of JPL’s Near Earth Object Program Office. “They will also become the fueling stops for humanity as we continue to explore our solar system. There is something about asteroids that makes me want to look up."
For people who have a telescope or some strong binoculars, maximum brightness, EarthSky reports, will occur between 11:07 p.m. and 11:52 p.m. EST on January 26. If you’re on the East Coast, sorry... our snow storm will make it unlikely that we’ll see anything.