The unnamed space rock referred to as the Asteroid (66391) 1999 KW4 is actually a double asteroid or a binary asteroid. That is, it consists of a large asteroid encircled by a smaller moon. In this case, it is about half a mile wide and orbits the larger body about every 16 hours.
The 1999 Las Cumbres Observatory describes KW4 as "slightly bruised at the poles and with a ridge around the equator that runs all the way around the asteroid. This ridge gives the primary part a walnut or gyro-like appearance.
While the KW4 was classified by the Minor Planet Center as a "potentially dangerous asteroid" in 1
This will be the second closest approach that KW4 has made in 1999 over the last two decades, and the next that will come to Earth by 2036, according to CNET. It will also be by far the largest object that is within about 20 lunar distances (4,647,790 miles) from us this year.
The next approach takes place on Saturday at 19:05. EDT (23:05 UTC) and will be the cheapest for observers in the southern hemisphere. The people of the northern hemisphere have to wait a day or two after the next approach until the asteroid reaches our southern horizon.
If you want to try to recognize him, read the helpful tips and diagrams provided by NASA Solar System Ambassador Eddie Irizarry at EarthSky.