The size is large enough for widespread destruction, and the distance is close enough for earths gravity to modify its orbit for future close approaches, I'll surmise. On Mar 6, 2013 12:14 PM, <jcarman6@q.com> wrote:

There is a fun little quiz about asteroids at the space.com website. Link follows

http://www.space.com/20085-asteroid-buzzes-earth-this-weekend.html

One of the questions is:

What is a potentially hazardous asteroid?

a. Any one that hits earth

b. One that is 500 feet wide and comes within 4.65 million miles of earth

c. One that is at least 1 mile wide and comes within 1 million miles of earth

I got this wrong, the correct answer is b. Does anyone know why b is the correct answer?

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