|(L) Ready to launch (R) Conception after launch|
Asteroids larger than 1 kilometer that could cause devastation on Earth had previously been estimated at one thousand objects but this survey implies the total will be close to 981, based on high-accuracy sampling of smaller areas. To date we know where 911 of those presumed 981 are. None represents a threat for the next few centuries. (Related story: Asteroid won't hit earth but how close will Apophis come? Updated )
The mid-size population between 100 meters and 1 kilometer in diameter had previously been estimated at 35,000 objects but the detailed sampling has tightened those numbers to about 19,500. This size could devastate a city but wouldn't de-stabilize the globe like the one that put an end to the dinosaur age. We've made progress and are now tracking just over 5,200 of these mid-sized asteroids.
The 10 to 100 meter population probably has a million objects, capable of delivering a nasty bump if they encounter earth.
|The image on the left represents the less dangerous solar system environment now identified.|
The dots representing asteroids are immensely exaggerated to be legible.
Update: But there are surprises. This link provided by Spaceweather.com shows all new discoveries, updated daily. There were over 100 in 2011. A 14 meter asteroid was discovered to be passing at 0.2 lunar diameters only about three days before it arrived January 27th. These "out of the blue" rocks are a small part of the total but can't be discounted.