Large asteroids, those more than 10 kilometers in diameter, are a favorite of science fiction disaster movies, but are actually the least common of all space rocks. And NASA is now confident that all such asteroids near Earth have been located and are being tracked, with none posing a threat to Earth in the next several centuries.
The Wide-field Infrared Survey Explorer (WISE) has imaged the complete sky twice since January 2010 and have found 911 of the 981 asteroids between 1 and 10 kilometers in diameter. While these asteroids are not potential planet killers like their larger cousins, they could significantly alter life as we know it on Earth.
Luckily, like the larger asteroids, none of the 911 discovered thus far pose an imminent threat. And while only 5,200 of the 20,000 medium sized asteroids (those 100 meters across) have been located, we appear to be safe from them as well. But there are still lots that we haven't seen.
Smaller asteroids, estimated to exist by the millions, could still pose a threat to Earth. They are a bit more difficult to detect as their infrared glow is more difficult to detect. So while there are many of these smaller asteroids that orbit out in the distance undetected, the WISE mission is still searching and over time should be able to locate, image and track many more of these rocks.
Image Credit: NASA JPL-Caltech
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