It's a scary thought, things dropping out of the sky, but astronomers keep a close eye on any objects which pose a risk of hitting the Earth. And now, a new scale is in use to indicate the risk of such an object impacting and causing serious damage.

At the UNISPACE III conference in Vienna today, the International Astronomical Union is announcing that it is has officially endorsed the scale, called the Torino scale, to gauge the potential impacts with asteroids and comets, according to an MIT press release.

The Torino scale, named after the Torino Astronomical Observatory in Italy, was developed by a professor at the Massachusetts Institute of Technology, Richard Binzel. It ranges from zero -- "events having no likely consequences" -- to ten -- "certain collisions ... capable of causing a global climatic catastrophe."

The chart is more likely to assuage fears of a "Deep Impact"-style armageddon than create unnecessary panic. Scientists have never identified an object that would have a Torino scale value greater than one -- an extremely unlikely collision.

NASA says the risks of a devastating impact are extremely low, but the immense damage an impact could cause on the global environment warrants concern.

The agency funds three programs which search for near-Earth meteors and asteroids. The Spacewatch Program, conducted by the University of Arizona, searches 200 square degrees of sky per month for objects. The NEAT program, done out of NASA's Jet Propulsion Laboratory, searches the night sky with an Air Force deep-space surveillance camera. A program at the Lowell Observatory, in Flagstaff, Arizona, has the potential to search 4,300 square degrees of sky per month.

Earth-bound asteroids will be the topic of a five-day international space conference held at Cornell University beginning on July 26.