Asteroids hit the Earth. It's an eventual reality, and one with which we must deal.
But we have to know where they are in the first place. That's not so easy: they are moving targets, and they have to be observed over a period of time to nail down the orbit. Even when the orbit is determined, small errors in the position (due to atmospheric turbulence messing up the observations, tiny errors in measurements just from statistics, and so on) can add up to large uncertainties in the position of a rock over time.
One such asteroid was found in September 1960, but the orbit wasn't well-determined, and the object was lost. It appears now that it's been found again! Object 2007 RR9's orbit matches what was known about an object once called 6344 P-L, and it's thought that these two are, in fact, one and the same object.
It appears to be more like a burned out comet nucleus than a standard rocky asteroid. It's not precisely clear from the press release, but it's implied that the orbit is similar to that of a meteor shower called the Gamma Piscids, which occur in October and November. Meteor showers are associated with comets, which may be why they're saying this is a dead comet and not an asteroid. Also, there is a number called the Tisserand parameter, which is associated with objects that undergo gravitational encounters with planets. Comets and asteroids tend to have different Tisserand parameters, and this object seems to fit in better with comets.
The rock -- whatever the heck it is -- has a 4.7 year orbit that takes it out near Jupiter, then back in. It crosses the Earth's orbit, making it a potential impactor. It won't hit us any time soon, but it will pass the Earth on November 7th at a distance of about 6 million miles. Close, but not too close. Don't expect to see it, though: at a magnitude of 18 or so it's 0.00002 times as bright as the faintest star you can see with your eye. You'd need a pretty good 'scope to see it at all.
This is all very cool. You may note that I am writing a book about astronomical events that can wipe out life on Earth, so I follow this sort of thing carefully (I would anyway, because it's cool). I'm glad that astronomers are out there looking for these things, and that we're smart enough to be able to work out their trajectories.
Now, if only our government were smart enough to fund this research better...