You can find this article in, coincidentally, May's issue of Astronomy (the magazine). If you're not familiar with it, it's reputable and is found on almost any store's newsstand in North America (and possibly other countries??)
Asteroid 99942 Apophis will be passing approximately 22,000 miles from Earth on April 13 of 2029. What sets it apart from most other Near Earth Objects (NEOs) is that further observations almost eliminate any chance of them impacting Earth. With Apophis on the other hand, every subsequent observation of the asteroid increased the probability that it would strike.
On December 18, 2004, and a few days following, several observations...
enabled the risk-assessment software at NASA's NEO Program Office and at the University of Pisa in Italy to compute the odds of an impact. There was a 1-in-300 chance the asteroid would strike Earth April 13, 2029. More observations filtered in. On December 24, the chance of an impact jumped to 1 in 60. Then, on Christmas Day, it rose to 1 in 42. It reached a maximum of 1 in 37 December 27. This trend is unusual. For nearly all NEOs, the odds of an impact decrease as more observations contribute to the analysis.
To put this in perspective, it's about 2 to 4 times the energy released when Krakatoa, a volcanoe in Indonesia, blew up in 1883. The blast and the after effects killed more than 36,000 people, mostly by tsunamis, which swept away 165 coastal villages. It's also 15 times more powerful than a nuke set off by the Soviet Union in 1961 with the force of 58 megatons of TNT, the most powerful ever detonated.If there was a bright spot in the events of that December, it involved estimates of the asteroid's size, which started out at 500m (550 yards). Size estimates decreased as the impact probability rose. Astronomers now think Apophis measures about 320m (350 yards) across. Despite it's smaller size, a collision would still pack a walop: The asteroid has the striking power of 870 megatons of TNT.
But Apophis will still miss Earth by a mere 64,000 km (40,000 miles). Something like this only happens roughly every 1300 years or so.On the same day the announcement was made of an impact risk of 1 in 37, a search for pre-discovery images of the asteroid brought in more data for analysis. New calculations based on the expanded set of observations now spanning 287 days, dropped Apophis' strike risk to below 1 in 10,000.
Then at the end of January of 2005, the Arecibo radio telescope was trained on the asteroid and refined it's orbit to within 34,400 km (22,000 miles). But it's not over yet, they have refined the orbit to eliminate all but one resonance keyhole. They explain that a resonance keyhole is a small region of space that if the asteroid were to pass through it, its course would be altered due to Earth's gravity.... and this particular keyhole would lead to a collision in April of 2036. Although the odds are still slim (about 1 in 5000) Apophis' orbit is so close to this keyhole that scientists can't rule out the possibility at this time.
Another interesting fact about Apophis...
There is a scale called the Torino scale, numbered from 0 to 10 where 0 = no threat and 10 = catastrophe. Most NEO's so far have reached a level of 1 before dropping down to 0 and only a few have reached 2. Apophis achieved a rank of 4 - defined as a close encounter that merits attention by astronomers.
I hope you found this interestingNo other NEO has ever posed this great a threat to Earth.
.... I hope in that year I'm in either Asia or North Africa to witness this!!!
