NASA Refines the Path of Asteroid Apophis, Again

Last Wednesday, October 7, NASA announced updated calculations on the path of Asteroid 99942 Apophis. Discovered June 19, 2004, is a near-Earth asteroid approximately 250 yards across—the length of two-and-one-half football fields.

Apophis was initially thought to have a 2.7 percent chance of striking Earth or Earth’s moon in 2029. Additional observations ruled out the possibility of a 2029 impact, but this led to a concern that on that 2029 pass Apophis might move through a region of space no more than about 600 meters across—called a gravitational keyhole—that would set up Apophis for an Earth impact on April 13, 2036. This concern was maintained until August 2006, when more observations ruled out this possibility. With the October 7 announcement, the probably of an April 13, 2036 impact is calculated as 1 in 250,000. While this is a good thing, Apophis will still go into the record books during its pass on Friday, April 13, 2029. On that date, Apophis is expected to come closer than 29,450 kilometers (18,300 miles) from Earth’s surface. Let’s put that distance in perspective.

- Earth’s moon orbits at about 384,400 km (238,900 mi), which is 354,950 km (220,600 mi) above the Apophis pass.

- Geosynchronous satellites—including communication and television satellites—orbit at about 35,786 km (22,236 mi), which is 6,336 km (3,936 mi) above the Apophis pass.

- Global Positioning System (GPS) satellites orbit at about 20,200 km (12,550 mi), which is 9,250 km (5,750 mi) below the Apophis pass.

- NASA’s Hubble Space Telescope orbits at 559 km (347 mi), which is 28,891 km (17,953 mi) below the Apophis pass.

- The International Space Station orbits at an average distance of 347 km (187 mi), which is well below the Apophis pass.

What have we learned from this? Well, we’ve learned that while Apophis will not actually strike Earth, it will definitely pass through Earth’s network of satellites. That may mean nothing. Could Apophis hit a satellite on its way through? Probably not. After all, there is a lot of space up there. Though, as we have seen in the last year or so, some things are able to beat the odds from time to time, and run into each other up there. Of course, the event is still 20 years in the future and who knows how many satellites will be in orbit by then? Low-probability satellite impacts aside, could the passage of Apophis influence our satellite network? Again, probably not, but it definitely continues to bear close watching for the scientific interest.

Beyond 2029, the latest calculations show another possible close encounter with Earth in 2068 with a chance of impact currently estimated at approximately three-in-a-million. This estimate is expected to be more highly refined, with the risk probably diminishing, as additional years of observations are made.

The prediction of asteroid orbits is a science based on a physical model of the solar system which includes the gravitational influence of the sun, moon, other planets and the three largest asteroids—Ceres, Pallas and Vesta.

Asteroids and comets which pass close to Earth are detected by NASA using both ground and space-based telescopes. The Near-Earth Objects Observations Program, also known as “Spaceguard,” discovers these objects, characterizes a subset of them and plots their orbits to determine if any object could b potentially hazardous to those of us on Earth. For more information about asteroids and near-Earth objects, check out these links:

Twitter Page for NASA’s Asteroid Watch
http://twitter.com/asteroidwatch

NASA’s Asteroid Watch
http://www.jpl.nasa.gov/asteroidwatch

NASA’s Near-Earth Object Program
http://www.jpl.nasa.gov/asteroidwatch

-