In case you are tired about end-of-the-world scenarios that feature global warming predictions, here is something for a change: 99942 Apophis is an near-earth asteroid with a diameter of roughly 300 meters. It orbits the sun but crosses the path of earth. According to present day observation, it is estimated to hit the earth in 2036 with a probability of about 1-in-45,000 [source] .
The asteroid, initially named 2004 MN4, was discovered on 19 June 2004 by Roy Tucker, David Tholen and Fabrizio Bernardi of the University of Hawaii Asteroid Survey (UHAS), from Kitt Peak, AZ. In December 2004, preliminary observations showed it might strike in 2029 when the asteroid will come closer to earth than some of our satellites. But further investigation ruled out the 2029 impact scenario. The possible impact in 2036 however can not yet be ruled out.
Astronomers rate dangerousness of asteroids and comets on the Torino Impact Hazard scale. The higher the value, the more dangerous the object. Apophis reached 2 out of 10 [source] that is "A discovery, which may become routine with expanded searches, of an object making a somewhat close but not highly unusual pass near the Earth." Moving scores 5 out of 10 "A close encounter posing a serious, but still uncertain threat of regional devastation."
To accurately predict the risk, the Planetary Society offers $50,000 in the Apophis Mission Design Competition to design a mission to rendezvous with and "tag" the asteroid, i.e. leave a device on the asteroid that allows tracking it very precisely. The deadline for the competition was on Friday, Aug. 31st 2007. According to their website, more than 100 teams and individuals from 25 nations intend to contribute to the mission.
But here comes the fun: You can estimate the consequences of an impact online on this interactive Catastrophe Calculator (calculate your own crater!), provided by the Dept. of Planetary sciences at the University of Arizona. For the visually and rethorically upgraded version, see NOVA: The asteroid that hit LA. (So much about 'catchy' titles.)
To the younger readers out there: here is your chance to save the planet! Needless to say, intimate knowledge of physics is necessary for this noble task.