The real story on Apophis’ close shave

Posted by David Eicher
on Thursday, January 10, 2013

The iTelescope T5 instrument at Siding Spring Observatory in Australia captured the asteroid Apophis on January 9. Apophis currently glows dimly at magnitude 16.1 and looks rather meek. // Credit: iTelescope Project
Yesterday’s close passage of the potentially hazardous asteroid (99942) Apophis, at a distance of 9 million miles (14 million kilometers), set off a wave of new social media discussions over doomsday scenarios. (After all, the asteroid was named for the demon serpent of Egyptian mythology.) Astronomers at Kitt Peak National Observatory discovered Apophis in 2004, and soon thereafter they found that it will make close passages to Earth in 2029 and 2036. The impact from an object like Apophis, which measures 700 to 1,100 feet (200 to 300 meters) across, would be terrible, at least regionally. But the new round of alarm bells over the possibility of an impact with Earth is unfounded.

Refinements in studying the orbit of Apophis have ruled out an impact in 2029. However, the asteroid will make a close shave, if you will, with Earth on Friday, April 29 of that year, passing just 18,300 miles (29,500 km), or 4.6 Earth radii, from the surface of our planet. That’s as close to Earth as some of our geosynchronous satellites — pretty impressive, but no impact. That will be a treat for amateur astronomers as the asteroid will be visible as a naked eye object of around 3rd magnitude.

A second close approach of Apophis will take place April 13, 2036. However, astronomers from the Jet Propulsion Lab in Pasadena suggest that new measurements on the orbit will most likely show Apophis will then pass some 30.5 million miles (49.1 million km) from our planet — a third the distance from Earth to the Sun.

So Apophis, much ballyhooed on the Web these days for the danger it poses, almost certainly will bring no more threat to us than the Mayans did with their calendar.

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