In the movies, it takes an existential threat to the entire planet to get the contentious nations of the world to unite against a common enemy. No doubt Earthlings would put their petty differences aside to defend humanity against alien invaders.

Last Friday, the world took a first step against a common threat from beyond our planet. The meeting at the United Nations between several nations and a contingent of astronauts and cosmonauts was not about defending against a hypothetical invasion by a superior alien force. It was about something far more likely, but just as lethal -- a catastrophic asteroid strike on the Earth.

In coming decades more than a million asteroids known as NEOs, or near-Earth objects, could pose a threat to the planet. Scientists have detected only a fraction of those traveling in the radius of Earth's orbit with the sun.

If an extinction-level NEO is spotted too late, little can be done. The goal of a proposed United Nations effort would be to detect the threat early and unite nations behind a common plan to deflect asteroids from a collision course with Earth.

Developing a unified response will require diplomatic and technological cooperation on an unprecedented scale, not to mention much funding. The overall plan presented at the United Nations last week had the barest of outlines.

Still, the General Assembly agreed to set up an International Asteroid Warning Group to share information. Details have to be worked out, but the United Nations agreed that it's important to get the effort up and running because it will take years to implement. The group that met with the United Nations called for a practice launch to deflect a smaller, non-threatening asteroid to see what is technologically feasible. They believe the technology to deflect asteroids exists, but the techniques to do so safely need to be practiced and developed.

The asteroid that exploded over Russia in February wasn't detected until it was on top of the planet. That NEO was only the size of a truck, but it did a lot of damage and injured more than 1,000 people. Other asteroids that dwarf it are silently orbiting Earth's neighborhood. What we don't know about them can definitely kill us.