Mile-Wide 'Walnut' Asteroid With Its Own Moon To Fly By Earth Saturday

(CBS Local) -- An asteroid nearly a mile wide with a moon of its own is expected to pass by Earth on Saturday, traveling at 48,000 mph.

The unnamed space rock designated as Asteroid (66391) 1999 KW4 is actually a double asteroid or a binary asteroid. That means it's composed of one large asteroid orbited by a smaller moon. In this case, it's about a third of a mile wide and orbits around the larger body about once every 16 hours.

The Las Cumbres Observatory describes 1999 KW4 as "slightly squashed at the poles and with a mountain ridge around the equator, which runs all the way around the asteroid. This ridge gives the primary an appearance similar to a walnut or a spinning top."

While 1999 KW4 is classified as a "Potentially Hazardous Asteroid" by the Minor Planet Center, it should clear Earth at a very safe distance of 3,219,955 miles. To put it in perspective, that's more than 13 times the distance from the Earth to the moon.

It will be the second-closest approach 1999 KW4 has made in the past two decades, and the nearest it will come to Earth until 2036, according to CNET. It'll also be by far the largest object to come within about 20 lunar distances (4,647,790 miles) of us this year.

The closest approach will happen Saturday at 7:05 p.m. EDT (23:05 UTC) and will be most favorable for observers in Earth's Southern Hemisphere. People in the Northern Hemisphere will need to wait until a day or two after closest approach for the asteroid to come over our southern horizons.

If you want to try to spot it, check out the helpful tips and charts provided by NASA solar system ambassador Eddie Irizarry over at EarthSky.