When scientists discovered the asteroid in 2004, they gave it a 2.7 percent chance of impacting earth in 2029. That possibility was later ruled out, but there still remained a slim chance of another collision during Apophis’ pass in 2036. Such an impact has been estimated as equivalent to about 510 megatons, which is equal to about 100 times the energy released by Tsar Bomba, the most powerful nuclear weapon ever tested.
But now, observations taken during the asteroid’s flyby this week have helped to rule out that apocalyptic scenario.
"The impact odds as they stand now are less than one in a million, which makes us comfortable saying we can effectively rule out an Earth impact in 2036,” Don Yeomans, the manager of NASA’s Near-Earth Object Program Office, said in a statement Thursday. “Our interest in asteroid Apophis will essentially be for its scientific interest for the foreseeable future."
As of Friday, NASA had pegged the chances of Apophis impacting Earth on Easter Sunday in 2036 as 1 in 10.9 million.
The latest data shows that the flyby in 2029 will be the closest for an asteroid of Apophis’s size (the space rock is as wide as about three-and-a-half football fields), coming as close as 19,400 miles above Earth’s surface.
However, close shaves with asteroids are a pretty common occurrence for Earth. Next month, an asteroid 40 meters (131 feet) wide will whiz by at 17,200 miles above the planet.
Apophis is an asteroid of significant scientific interest, though. The European Space Agency’s Herschel observatory, currently in orbit around Earth, made new observations of Apophis during its latest approach.
Previously, scientists had thought the asteroid’s average diameter was something around 270 meters (885 feet) wide; the latest data from Herschel suggests that it’s actually around 325 meters (1,066 feet) across. Apophis also turns out to be brighter than previously estimated, with an albedo of .23, meaning that 23 percent of the sunlight that falls on the asteroid is reflected.
Albedo could hold the key to deflecting dangerous asteroids in the future. Photons bouncing off of a space rock could provide enough force to alter an asteroid’s orbit, but to make a difference, the asteroid would have to be made as brilliantly white as possible.
One MIT graduate student won a United Nations prize in October for his proposal, which involved changing Apophis’ orbit by shooting it with paintballs. Both coating the asteroid with paint and the impact of the paint pellets would provide enough force to turn Apophis away from a hypothetical collision course, according to the proposal.
Other options that have been proposed include using clouds of tiny spacecraft, or solar sails, that would tug an asteroid out of harm’s way.
“It is very important that we develop and test a few deflection techniques sufficiently so that we know we have a viable ‘toolbox’ of deflection capabilities to implement when we inevitably discover an asteroid on an impact trajectory,” NASA Near Earth Object Observation Program manager Lindley Johnson said in October.