The scientific world is buzzing about the approach of asteroid 2012 DA14, which will pass within 17,200 miles of Earth on Feb. 15, 2013. In galactic terms, that is a very close call, passing within the ring of satellites orbiting Earth; according to NASA, it is a record-close approach for a known object of this size, which is estimated at 150 feet. One look at the surface of the Moon reveals the record of impacts from comets and asteroids that have pummeled the inner solar system. The Earth has suffered the same fate, but the evidence has been erased or hidden by erosion, forests, water, etc. Several impacts from large asteroids are suspected in mass extinctions in the fossil record, including the well-known K-T extinction that killed off the dinosaurs 65 million years ago. But unlike the dinosaurs, we have the capability of space flight, and perhaps can do something about an asteroid threat. Here are five thoughts on how and why we are monitoring these threats from space — and how we might try to stop an extinction-level event.