Are there any asteroids on a collision course with Earth or is it all a Hollywood fiction?  How do we know if the Earth is safe and how do we estimate our chances of being struck?  What would we do if we did discover an errant asteroid headed our way?  All of these are questions that planetary astronomers have been working to answer over several years and for which good answers are now being found. 

The realization that impacts can and do occur on Earth is a profound conclusion achieved only after we explored other planets such as Venus and Mars and saw a continuing history of impacts recorded as craters on their surfaces.  Exploration of the Moon further attests to impacts happening close to home – and it is only through geologic sleuthing that we have finally recognized several hundred craters on Earth that have yet to be completely erased by erosion and weathering.  What’s more, the impact of comet Shoemaker-Levy 9 into Jupiter in 1994 vividly demonstrated that impacts are not something that only occurred in the solar system’s past.  Impacts are a continuing process in our solar system today.  As a species, our technological capability is just now reaching the point where we can discover potentially hazardous objects far enough in advance to plan a sensible course of action should an actual serious threat be identified.  That same technology holds the promise of increasing our scientific knowledge of these worlds and ultimately taking advantage of the natural resources they can provide to future space explorers.