But occasionally, something larger gets through.
Thats what happened off Russias east coast on December 18 last year.
So why didnt we see this asteroid coming?
And why are we only hearing about its explosive arrival now?
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NASA/JPL-Caltech/Center for Near Earth Object Studies
So where did this asteroid come from?
But smaller, more frequent collisions also pose a marked risk.
In 1908, in Tunguska, Siberia, avast explosionleveled more than 2,000 square kilometers of forest.
Due to the remote location, no deaths were recorded.
Had the impact happened just two hours later, the city of St Petersburg could have been destroyed.
In 2013, it was a 10,000-tonne asteroid thatdetonated above the Russian city of Chelyabinsk.
More than 1,500 people were injured and around 7,000 buildings were damaged, but amazingly nobody was killed.
The meteor trail taken about 200km away from Chelyabinsk a minute after the blast in 2013.
Flickr/Alex Alishevskikh, CC BY-SA
Were still trying to work out how often events like this happen.
Our information on the frequency of the larger impacts is pretty limited, so estimates can vary dramatically.
The truth is, we dont really know.
What can we do about it?
The result is theidentification of thousands of near-Earth asteroidsupwards of a few meters across.
The longer we can observe a given object, the better that prediction becomes.
But as we saw with Chelyabinsk in 2013, and again in December, were not there yet.
But finding asteroids is hard.
Surveys scour the skies,looking for faint star-like points moving against the background stars.
They can only be spotted when passing very close to our planet.
The vast majority of the time they are simply undetectable.
The Chelyabinsk impact is a great example.
Why not move the asteroid?
While we need to keep searching for threatening objects, there is another way we could protect ourselves.
This artists concept shows the OSIRIS-REx spacecraft contacting the asteroid Bennu.
Interestingly, ideas of asteroid deflection dovetail nicely with thepossibility of asteroid mining.
