W.I.S.E. Asteroid survey complete. Fewer dangers and the tally of the biggest almost done.

The WISE survey has put sharp upper limits on asteroid numbers and has identified nearly every one that is more than 1 km. across and capable of global devastation.  Sourced at Science Daily News.

(L) Ready to launch    (R) Conception after launch

NASA launched WISE (Wide-field Infrared Survey Explorer) to survey the asteroid population at infrared wavelengths.  Dull objects that don't reflect light into regular telescopes become visible in infrared light and this heat signature depends on the asteroid's size, not on how shiny it is.  In the last year, WISE did two complete scans that identified more than one hundred thousand objects in the general population of the belt between Mars and Jupiter.   

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.

Current asteroids of interest are calendared at Spaceweather.com, listing any above 10 meters which come closer than one hundred times the distance from here to the moon.

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.