NASA launches spacecraft to kick an asteroid off course

A NASA mission to deliberately smash a spacecraft into an asteroid -- a test run should humanity ever need to stop a giant space rock from wiping out life on Earth -- blasted off Tuesday from California.

It may sound like science fiction, but the DART (Double Asteroid Redirection Test) is a real proof-of-concept experiment, which lifted off at 10:21 pm Pacific Time Tuesday (0621 GMT Wednesday) aboard a SpaceX rocket from Vandenberg Space Force Base.

"Asteroid Dimorphos: we're coming for you!" NASA tweeted after the launch.

The goal is to slightly alter the trajectory of Dimorphos, a "moonlet" around 525 feet (160 meters, or two Statues of Liberty) wide that circles a much larger asteroid called Didymos (2,500 feet in diameter). The pair orbit the Sun together.

Impact should take place in the fall of 2022, when the binary asteroid system is 6.8 million miles (11 million kilometers) from Earth, almost the nearest point they ever get.

"What we're trying to learn is how to deflect a threat," NASA's top scientist Thomas Zuburchen said of the $330 million project, the first of its kind.

To be clear, the asteroids in question pose no threat to our planet.

But they belong to a class of bodies known as Near-Earth Objects (NEOs), which approach within 30 million miles.

NASA's Planetary Defense Coordination Office is most interested in those larger than 460 feet in size, which have the potential to level entire cities or regions with many times the energy of average nuclear bombs.

There are 10,000 known near-Earth asteroids 460 feet in size or greater, but none has a significant chance to hit in the next 100 years. One major caveat: scientists think there are still 15,000 more such objects waiting to be discovered.