A massive"planet killer" asteroid will make a very close approach to Earth later this week, safely zipping past our planet at around 58,000 mph . 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.
2011 UL21 is likely at least 10 times smaller than the largest space rock to ever hit Earth, the Vredefort asteroid, and around five times smaller than the rock that wiped out the dinosaurs around 66 million years ago.
Although the space rock poses no threat to Earth — either now or in the future — it is interesting because it's probably one of the 10 biggest asteroids to pass within 4.7 million miles of our planet since 1900, Gianluca Masi, an astrophysicist and director of the Virtual Telescope Project , wrote in a recent statement.