That doesn't mean it won't come close to the Earth, though, as 22,364 miles is even inside the orbit of geosynchronous satellites [which are 26,000 miles up]. Still, while we appear to be safe in 2029, there is a minor chance (about 1 in 250,000) that it could hit the Earth when it returns again in 2036.
It is expected that once the 2013 flyby is complete, astronomers will be able to more closely determine distances involved in the 2036 pass, and rule out an impact.
As the asteroid approaches, though, its specifications become clearer. European Space Agency (ESA) officials announced on Wednesday that its infrared Herschel Space Observatory has discovered that Apophis is about 1,066 feet wide, which is nearly 20 percent larger than a previous estimate of 885 feet.
Study leader Thomas Müller of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, said in a statement:
The 20 percent increase in diameter translates into a 75 percent increase in our estimates of the asteroid's volume or mass.NASA previously calculated that if Apophis struck the Earth it generate a blast with the energy equivalent to over 500 megatons of TNT. In comparison, the most powerful hydrogen bomb ever detonated was the Soviet Tsar Bomba, which released 57 megatons of energy.
Based on being dubbed a "doomsday asteroid," one might expect that if Apophis impacted the Earth it would result in an Extinction Level Event (ELE, per "Deep Impact").
Both live webcasts of asteroid Apophis will be available here tonight. The Slooh Space Camera webcast will begin at 7 p.m. EST (0000 Jan. 10 GMT). The Virtual Telescope webcast will begin an hour later at 8 p.m. EST (0100 GMT).
If you want to track Apophis' position directly, you can do so via the Virtual Telescope Project here.