Scientists have proposed that the United Nations establish a global network of telescopes to track asteroids and comets at risk of hitting Earth—and, eventually, create a plan to deflect them and evacuate humans in their paths. The Association of Space Explorers (ASE) is set to deliver its recommendations to the U.N.'s Committee on the Peaceful Uses of Outer Space when the panel meets in February. If the committee signs off on them, they would go to the General Assembly for final approval.

"The U.N. has 192 member states, and very few are aware of near-Earth objects," says Hans Haubold, a spokesperson for the U.N. Office for Outer Space Affairs. "We welcome this initiative, but it is up to the [U.N.'s] member states to decide what to do with it."

Near-Earth objects (NEO's) are asteroids or comets whose orbits intersect with or come close to crossing Earth's orbit around the sun. The massive space objects, rocky or metallic asteroids and comets made of ice and dust, are remnants from the formation of the solar system, and the former are sometimes specifically referred to as near-Earth asteroids (NEAs). Asteroid and comet impacts have been blamed for catastrophic events in Earth's history, such as wiping out the dinosaurs 65 million years ago and, it is thought, destroying a large swath of Siberian forest a century ago.

The frequency at which NEOs slam into our planet is inversely proportional to their sizes: Those that are tens of yards (tens of meters) in diameter (the size of a small building) might hit our planet once every few decades, whereas NEOs whose diameters are several miles (kilometers) might strike once in many millennia, says John Pike, founder of the informational Web site

NASA's global Deep Space Network of radio telescopes placed in California, Spain and Australia, primarily used to communicate with spacecraft, are also trained on the cosmos and tracking NEOs; there are also observatories in other parts of North America and Europe as well as in Japan, India, Brazil, China and Argentina. "But they are not well coordinated on worldwide basis," Haubold says.

The ASE and other organizations such as the B612 Foundation are working to prevent another catastrophic impact like the one that did in the dinos. B612, chaired by former astronaut Rusty Schweickart, advocates a "space tug" that would involve flying a spacecraft near to an approaching NEO; the gravitational pull of the spacecraft would slightly alter the rock's course to nudge it out of an Earth-impacting orbit. (Schweickart also chairs the ASE's near-Earth object committee.)

To see the impact of the 1908 Tunguska event, check out our slide show.

(Image of Manicouagan Crater/NASA)