Thursday/ asteroid watch

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.

YearAsteroids > 100 m (except 2013)SizeLunar Distance
2004Toutatis5,000 m (3.1 mi)4
Nov 2011(308635) 2005 YU55360 m (1,180 feet)0.84
Dec 20112011 XC2100 m (328 feet)0.9
2013Chelyabinsk meteor20 m (65 feet)0
20172014-JO25 'The Rock'650 m (2,000 feet)4.7
A graphical representation of the size of the asteroid thought to have killed the dinosaurs, and the crater it created, compared to an asteroid thought to have hit the Earth 3.26 billion years ago and the size of the crater it may have generated. A new study reveals the power and scale of the event some 3.26 billion years ago which scientists think created geological features found in a South African region known as the Barberton greenstone belt. Credit: American Geophysical Union

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