Reply #20: NASA Details [View All]

2004 MN4 has several opportunities. 2029 is the highest probability. I think it might get tricky to project after that since a close encounter is likely to alter a close Earth fly-by.

http://neo.jpl.nasa.gov/risk/2004mn4.html

~7.9e+10 kg at 12.59 km/s. Estimated impact energy: 1490 Megatons. That's nasty.

I doubt it is practical to blow up a 400-meter asteroid. Best bet, if an impact is highly probable, is to nudge it a bit when it is at perihelion. There would be a number of opportunities to do this in the years prior to 2029. I remember seeing some "Back or the envelope" calculations back in the 80's that suggested this could even be done without nuclear weapons even for larger rocks than this. The trick is to make absolutely sure that we are reducing, rather than increasing the likelyhood of collision.

It appears from the orbit that the asteroid will be "catching up" from us from below the ecliptic where the orbits intersect. I'm not sure if this means a southern hemisphere impact slightly is more likely.