[RightWhale]

The orbits of asteroids and comets that cross the orbits of planets are diverted by the planets. The amount of diversion is very sensitive to how close the body passes to the planet. It is not possible to calculate exactly where an earth orbit crossing asteroid will be several orbits later since the net diversion will multiply. A probability of passing through an area of space can be calculated, but not the exact position.

[Eagles Talon IV]

Are the planets or other asteroids this particular one will pass by not known already? It seems if this asteroid can be identified 29 years out, so then can the celestial bodies it will come near. It's just mathematics and it seems as if someone has done their homework if the probability of a collision is at .018%

I don't know this for a fact but it is probable that ones chance of being struck by lightening is greater then that.