Discovered back in 2004, the Apophis asteroid garnered lots of attention when initial calculations of its orbit indicated that there was a 2.7 percent chance that it would hit Earth when it did a flyby in 2029. After running additional calculations based on the asteroids data, scientists were able to rule out a 2029 impact, but there was still a remote possibility that it might hit Earth during another flyby in 2036. However, that estimate has also been revised.
Thanks to the European Space Agency’s Herschel Space Observatory, a number of thermal infrared observations were captured of Apophis at different wavelengths. Taken together with optical measurements, Hershel was able to refine earlier estimates of the asteroid’s properties, which included its overall diameter. Initially, it was estimated to be 270 m on a side but now stands at a robust 325 m, an increased which translates into a 75% increase in its volume.
The thermal readings on the asteroid also provided a new estimate of the asteroid’s albedo, which is the a measure of its reflectivity. Knowing the thermal properties of an asteroid indicates how its orbit might be altered due to subtle heating by the Sun. Known as the Yarkovsky effect, the heating and cooling cycle of a small body as it rotates and as its distance from the Sun changes can instigate long-term changes to the asteroid’s orbit.
All of this taken together, has allowed NASA, the ESA and other space authorities to rule out the possibility of an impact by 2036 as well. Don Yeomans, manager of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory:
“We have effectively ruled out the possibility of an Earth impact by Apophis in 2036. 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. Our interest in asteroid Apophis will essentially be for its scientific interest for the foreseeable future.”
But the flyby on April 13, 2029 will be one for the record books, says NASA. On that date, Apophis will achieve the closest flyby of an asteroid of its size when it comes to within 31,300 kilometers (19,400 miles) of the Earth’s surface. And in the meantime, an smaller asteroid (40 meters in diameter) named 2012 DA14 will make an ever closer flyby as it passes Earth at a distance of 27,670 km (17,200 miles).
So people can rest, safe in the knowledge that no asteroids are likely to hit us anytime soon. But at the same time, apocalyptics can rest assured that there will be plenty of remote chances to exploit for the sake of their unusual brand of paranoia. As Yeomans said:
“With new telescopes coming online, the upgrade of existing telescopes and the continued refinement of our orbital determination process, there’s never a dull moment working on near-Earth objects.”