99942 Apophis, a near-Earth asteroid that orbits the sun every 324 days, briefly raised a few hairs on the backs of astronomers after its discovery in 2004. Early orbital calculations gave it a 2.7 percent probability of striking Earth during a close flyby in 2029.
A later study of older photos that happened to include the asteroid helped to refine its orbit and eliminate the impact possibility that year. Unfortunately it also pointed to the chance for another potential strike in April 13, 2036.
During the 2029 flyby, it was predicted that Apophis might pass through a gravitational keyhole, a narrow region of space (just 1/2 mile wide in this instance) where Earth’s gravity alters the asteroid’s path in such a way as to set it on a future collision course. While remote, the possibility was enough to cause concern.
Thanks to fresh data gathered when Apophis zipped 9.3 million miles from Earth this Wednesday Jan. 9, we can now breath a sigh of relief.
Astronomers used NASA’s Goldstone 230-foot radar dish as well as the Magdalena Ridge Observatory in New Mexico and Pan-STARRS observatory in Hawaii to track the asteroid and determine a very accurate orbit.
“With the new data … we have effectively ruled out the possibility of an Earth impact by Apophis in 2036,” said Don Yeomans, manager of NASA’s Near-Earth Object Program Office at JPL. “”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.”
If you’re a catastrophist, don’t get too down about the news. The April 13, 2029 appearance will be the closest flyby we’re aware of of an asteroid this big. On that date, Apophis will pass only 19,400 miles from the surface of Earth and shine brightly enough (mag. 3.5) to be visible with the naked eye from suburban skies.
Viewing conditions will be ideal in Europe, Africa and the Middle East observers with dark skies during closest approach on the 13th; U.S. observers won’t be as fortunate. When Apophis is nearest and brightest, the sun will still be up in the sky. The best views for the States will happen on the evening of the 12th, when you’ll see it in binoculars as a 7th magnitude point of light low in the southern sky. When darkness falls on the 13th in the U.S., you’ll need an 8-inch or larger scope to spot it.
Speed and proximity are behind Apophis’ dramatic change in brightness over such a short span of time. It tears by Earth at such a high rate of speed that it brightens and fades in hours instead of days or weeks.
Apophis was originally thought to be 885 feet across, but that number was refined this week when the European Space Agency’s orbiting Herschel Space Observatory made a series of observations in infrared light during the asteroid’s approach. When those observations were combined with visual light data, scientists were able to come up with a more accurate estimate of it size. It grew! Apophis’ measures 1,066 feet +/- 50 feet across.
It’s also darker than previously thought which affects how much sunlight it absorbs. That in turn can lead to changes in Apophis’ orbit over time. Astronomers won’t be taking their eye off this monster rock anytime soon. You can read more about the findings HERE.