how often do impactors about 10 km in size hit the Earth?

Answer 1

Not often enough, LOL!

Answer 2

The graph mentioned by braxton_paul is good but a better one was published by Peter Brown et al. in the journal Nature in 2002. Their graph shows an annual event of about 5 kilotons and reduced probabilities for the other events. Tunguska is nearly once a century on the former plot but more like once every 1000 years on the latter.

At present we only know of 3 asteroids around 10 km in diameter that come nearish to the Earth. None of them will hit the Earth any time within the next century or more,, if ever. We haven't found any more of that size for the last 15 years and we have been looking a lot harder in the last 7 to 10 years.

Answer 3

An object that large striking the Earth would do so on average every 100 million years or so. There's no way to know for certain when the next one will take place. There's some 1,500 to 2,000 near Earth asteroids big enough to either wipe us out or do horrendous damage that could strike the Earth astronomers know about, and no telling how many comets that could strike like a bolt out of the blue. That is because by the time a comet that is on a collision course with us is found, the impact would be at best months or a year away.

Answer 4

See the graph about 3/4 down the page at this website ==>http://www.schoolsobservatory.org.uk/astro/textb/solsys/neo_prob.htm

Answer 5

The latest figures I remember seeing quoted once in 50 million years.

So, relax folks.

Except that the last one (that we know about) was 65 million years ago.

Answer 6

Nobody knows for sure, but probably less than once every million years.