An asteroid with its own moon will have a close encounter with Earth this weekend. The space rock known as asteroid 1999 KW4 will pass by our home planet at a speed of 48,000 miles per hour.
The asteroid was first discovered 20 years ago by the Lincoln Laboratory's Near Earth Asteroid Research survey (LINEAR) using the telescopes at the Experimental Test Site in White Sands Missile Range.
Measuring 0.8 miles, the object is massive enough it has its own moon. The asteroid and moon pair is thus technically designated as a binary system, which is defined as having two celestial objects close enough to orbit each other.
Potentially Hazardous Asteroid
The Minor Planet Center classified the asteroid as potentially hazardous, but scientists say it will pass by safely.
1999 KW4 is expected to have its closest approach to Earth at a proximity of 3,216,271 miles from our planet. This distance is equivalent to 13.5 times the distance between the Earth and the moon.
The asteroid will be the largest object to come within about 20 lunar distances of Earth this year.
The European Space Agency, which has been tracking the pair, said the asteroid binary is getting brighter ahead of its anticipated May 25 approach.
Second-Closest Encounter With Earth
The flyby will be 1999 KW4's second-closest approach to Earth in the past two decades. The event will also be the time when the asteroid gets nearest to Earth until 2036. The closest approach this weekend is anticipated to occur at 7:05 p.m. EDT (23:05 UTC) on Saturday.
Some of the world's biggest telescopes, which include the Arecibo radio observatory in Puerto Rico, will observe the flyby to gather data on both the asteroid and its moon. Among the objectives of the observations is to improve the model of the asteroid's shape and surface properties.
"In 2019, the asteroid will approach from the south, and the first day of visibility also coincides with the closest approach (May 25)," NASA said. "1999 KW4 is observable at Goldstone four days before it enters the beam at Arecibo."