Asteroid 2012 DA14 is set to fly by the Earth in mid-February; it's not huge (it would not produce an "extinction-level event" if it hit us), but neither is it just a "big rock". It's about half the length of a football field, and is thought to be similar to the one that exploded above a remote part of Siberia in 1908 - leaving a lake-sized crater and flattening trees for miles around. This latest asteroid is supposed to pass the Earth at a distance of about 17,000 miles (which is nothing in astronomical terms), and is within the "High Earth Orbit" range of some satellites. It's interesting that the 17,000 miles figure was revised downward from an earlier distance given by NASA as around 21,000 miles late last year, and that NASA is going to "ping" the asteroid daily by radar, starting Feb 6th. They do state there no chance it will impact earth, and almost no chance it will hit any satellites or other space debris.