A massive "planet killer" asteroid will make a very close approach to Earth today (June 27), safely zipping past our planet at around 58,000 mph (93,000 km/h). The "potentially hazardous," mountain-size object is one of the largest space rocks to pass close to Earth in more than a century — and you can watch the close encounter live.
The asteroid, 2011 UL21, is a near-Earth asteroid, meaning its orbit occasionally puts it within 1.3 astronomical units (AU) of the sun — or roughly 1.3 times the average distance between Earth and the sun.
