A thirty-thousand mile miss is the concensus from astronomers now. Last week, 2007WD5 was given a three percent chance of hitting Mars and digging out a crater about as big as this Arizona one on the left.
Whenever a rock passes this close to Mars, its orbit will be significantly altered. It’s not enough to catalogue all possible dangers to the Earth, but to keep close tabs on those that dodge other planets. Most planet-crossing bodies are in unstable orbits and require monitoring.
Catholic Sensibility 