> Why hasn't Jupiter gobbled this one up yet?
Because the asteroids orbit goes nowhere near Jupiter.
So Jupiter hasn't been the solar system vacuum for billions of years?
Those comets and asteroids have been awfully plentiful on our short life spans. Shumaker-Levy would have been life ending if it were to have hit earth. In our very lifetimes.
>> Why hasn't Jupiter gobbled this one up yet?
> Because the asteroids orbit goes nowhere near Jupiter.
There is nothing about the existance of this asteriod that is inconsistent with current models of the age of the Solar System.
Chunks of rock get kicked out of the asteriod belt every now and then. This one is has only been in its current orbis for a some millions of years. Evenutally it will hit Earth or fall into resonance with Venus, or Earth.
You can go here to visualize its orbit:
http://neo.jpl.nasa.gov/cgi-bin/db_shm?des=2004%20MN4
You can pan, zoom, enter dates and let it spin. Apparently the visualization only does Keplerian orbits, they do not account for "secular [non cyclical] effects".