Is an asteroid harmful

Answer 1

It's a rock. If it hits you, it will hurt.

Depending on the size, it may be anything from "Meh..." to "Ghaaak!" For example, we've just discovered that an asteroid will come fairly close, on an astronomical scale, to the Earth on Monday, June 27, 2011. It will miss, but it will be closer to Earth than any number of satellites. If the asteroid hits one of those satellites, the satellite will be destroyed.

This asteroid is about the size of a large bus. If it were to hit the Earth, it would most likely explode high in the atmosphere, causing no damage. If the asteroid were ten times bigger, it could cause a lot of damage, and if it were 1 hundred times bigger, it could destroy a city - if it hit.

But the bigger the rock, the rarer it is. We expect a bus-sized rock to hit Earth every decade or so, and things 10 times larger to hit once per century or so.