2011 UL21, also known as the "Planet Killer," was one of the largest asteroids to ever come this close to the blue planet. The stellar rock, which is known as 2011 UL21, had a massive width of 1.1 to 2.4 miles (1.7 to 3.8 kilometres) and passed Earth at a speed of approximately 58,000 mph (93,000
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