A large asteroid that ‘brushed’ by Earth (less than 5 lunar lengths away) on Wednesday was in the news recently, but I see we get smaller ones brushing by with a berth less than one lunar length just about every year. In 2013 there was the Chelyabinsk meteor, that made a spectacular entrance into the atmosphere, even though it was just 20 m (65 ft) across. So celestial objects larger than 100 m are serious trouble, since they might wipe out whole towns or cities.
Then there was the 10 km (6 mi) wide asteroid of 65 million years ago that killed the dinosaurs – and an even bigger one, thought to have hit Earth some 3.26 billion years ago, that was 37 km (23 mi) wide. That last one caused an earthquake that would have measured 10.8 on the Richter scale. Whoah.
| Year | Asteroids > 100 m (except 2013) | Size | Lunar Distance |
|---|---|---|---|
| 2004 | Toutatis | 5,000 m (3.1 mi) | 4 |
| Nov 2011 | (308635) 2005 YU55 | 360 m (1,180 feet) | 0.84 |
| Dec 2011 | 2011 XC2 | 100 m (328 feet) | 0.9 |
| 2013 | Chelyabinsk meteor | 20 m (65 feet) | 0 |
| 2017 | 2014-JO25 'The Rock' | 650 m (2,000 feet) | 4.7 |
