posted on Oct, 21 2012 @ 02:59 PM
reply to post by crappiekat
There are quite a few factors involved which will influence if something makes it to the ground, and also how fast it's going when it hits the
ground, including size, composition, angle of entry, and speed.
In most cases, large objects that enter the atmosphere usually break up at high altitude, and since small fragments don't keep their momentum,
anything that does survive is slowed down by air resistance and will reach the ground traveling at free-fall velocity (9 m/s squared).
In order to reach the ground traveling at enough speed to make a crater, an object would have to be very large (or large and very dense ie iron-nickel
- but there are fairly rare) - perhaps 10-15 m across. Objects this size hit us perhaps once or twice a decade.
At around 30-50 m, you are looking at significant localized damage on the ground. The object that caused the Tunguska blast was thought to be around
50m, and objects of this size hit on average once every 100 years or so.
Check out The American Meteor Society Fireball FAQs
, especially answer
This on-line impact calculator
is fun to play around with and try out various scenarios.