A very big asteroid with its own little moon is going to zip past Earth tonight (May 25) — close enough that, with some preparation and a decent telescope, amateur astronomers may spot it blotting out the stars.
This moon-and-asteroid system, called 1999 KW4, is made up of two rocks. The big one is about 0.8 miles (1.3 kilometers) wide, according to NASA, and shaped like a spinning top. The smaller one is more elongated and stretches 0.35 miles (0.57 km) along its longest dimension. It points lengthwise toward its much larger twin.
Together, the asteroid and its minimoon will pass Earth at such a strange, steep angle that NASA called them “the least accessible … for a spacecraft mission of any known binary near-Earth asteroid.”
But that doesn’t mean they aren’t interesting to look at.
The two asteroids will pass closest to Earth at 7:05 pm EDT (1105 GMT), when they’ll be just 3,219,955 miles (5,182,015 km) from the planet’s surface. That’s more than a dozen times the distance between the Earth and the moon in its orbit around our planet, and much too far for the space rocks to pose any threat. In fact, this is the fourth approach the binary asteroids have made toward Earth since they were discovered in 1999, and not the closest.