Don't worry if you miss it - 1999 KW4 will pass by Earth again on May 25, 2036.
And to further complicate matters, the space rock will shoot past the planet at breakneck speeds of 21.51km per second or 48,116mph.
The asteroid 1999 KW4 will swing past Earth.
An asteroid which measures approximately a mile wide and is orbited by its own moon is expected to pass by the Earth on Saturday, May 25, at speeds of 48,000 miles per hour. The larger one is just under a mile in diameter and its companion asteroid "moon" is about a third of that size.
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. The secondary is about 500 meters across, and the two asteroids orbit each other every 17.5 hours at a distance of about 1.6 miles". "This ridge gives the primary an appearance similar to a walnut or a spinning top".
The European Space Agency (ESA) on May 14 shared an image of the 1999 KW4, "observed from the ground for the first time in the current apparition, emerging from solar conjunction", it published on its official website.
The asteroid's Earth flyby will start May 24 and last until May 27. The two asteroids will remain visible for several days, though, according to EarthSky.
"In 2019, the asteroid will approach from the south, and the first day of visibility also coincides with the closest approach (May 25)", the USA space agency writes in documents found on its website.
EarthSky notes that this is the biggest asteroid to come so close to Earth for another decade; the next such close encounter is not expected until June 2027.