However, far more dangerous are asteroid fly-bys.
This link to space.com covers a recent one of an asteroid 100m across flying between the earth and moon. The line in the image on the left is the path of the asteroid 2012 XE54.
This was just recently discovered (as in the last few months or so).
You can see the fly-by here:
Some important points from the space.com article:
- Scientists have discovered about 9,000 near-Earth asteroids to date.
- A million or more such space rocks are thought to exist.
- Its thought that some 4,700 asteroids are 100 m wide and come uncomfortably close to our planet at some point in their orbits.
- Of these 4,700 large asteroids perhaps 30 percent of these large space rocks, which could obliterate an area the size of a state if they slammed into Earth, have been tracked.
- There are even larger asteroids, some 5km across, which would simply wipe out earth life.
Yet we whine and cry about "climate change."
And these large asteroids pass by with alarming frequency; many times we don't even know they are there until they get very close. There have been several in the last few years according to space.com.
Just one larger asteroid impact would significantly change climate for many years and perhaps wipe out all humanity.
Put apparently there is little government "funding" to study these known-to-exist but not tracked large asteroids.
Despite the bet Bruce Willis movies there would be little hope of humanity deflecting a very large asteroid. For example, use of high-orbit nuclear weapons for such a purpose would create a large-scale EMP that would destroy much of earth's electrical infrastructure. (And provide such a device could accurately be delivered and in sufficient time.)