Earth in no danger from asteroid flyby this week

An asteroid a half a football field across traveling at a blistering 4.8 miles per second is expected to pass within just 17,200 miles of Earth on Feb. 15, a record close encounter that will carry it well inside the orbits of communications satellites.

But scientists say a detailed analysis of its trajectory shows there is no chance asteroid 2012 DA14 will hit the Earth and very little chance of a collision with any satellites in geosynchronous orbits 22,300 miles above the equator.

"It's sort of threading the needle," Don Yeomans, manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif., told CBS News. "We know the orbit well enough that we can say definitely that it cannot hit the Earth and will not hit the weather or geosynchronous satellites."

Even so, several satellite operators have requested detailed asteroid trajectory data "so they can run them against their satellite ephemeris files to see how close this thing gets," Yeomans said. "There have been no problem (identified) so far."

Asteroid 2012 DA14 will make its closest approach to Earth above Indonesia at 2:24 p.m. EST Friday, covering the width of two full moons every minute as viewed from the surface. It will be the closest pass of an object this size or larger ever recorded.

Moving from south to north, it will not be visible to the unaided eye, but observers from Eastern Europe to Australia will have a chance to see it through telescopes or binoculars as a quickly moving pinpoint of light.

Amateur and professional astronomers alike will be making observations, collecting spectral data to help determine its composition, measuring changes in brightness and using powerful radars to image the object as it flies past.

"There will be a lot of folks doing photometry, measuring its light output to see how it's rotating, whether it's a fast rotator, a slow rotator, whether it's wobbling," Yeomans said. "There will be folks I would hope doing wide-band spectroscopy to try to understand whether it's a so-called S-type (asteroid), a silicate rock type, or whether it's carbon-based materials to understand its composition a little better. It's most likely a silicate rock type object, but who knows?"

Asteroid impacts are not uncommon. Yeomans said about 100 tons of material fall into Earth's atmosphere every day, including objects up to the size of basketballs. Car-size bodies impact the atmosphere every few weeks. Bodies the size of 2012 DA14 would be expected to impact the planet once every 1,200 years on average.

To put that in perspective, the dinosaurs are believed to have been wiped out by a six-mile-wide asteroid that struck the Earth 65 million years ago, triggering cataclysmic environmental damage on a global scale.

"There are about a thousand objects a kilometer and larger, and those are the ones we think could cause a global problem," Yeomans said. "But there are not many of them and they don't hit very often, you know, every 100 million years or so. And then at the lower limit, less than 30 meters, you wouldn't expect any damage, just a big old fireball. There are millions of those, maybe two million, and that's a guesstimate."

2012 DA14 was discovered last year by Spanish astronomers. Subsequent tracking showed the 150-foot-wide object is in an orbit similar to Earth's, making repeated flybys. This time around, however, the asteroid will pass so close that Earth's gravity will change its trajectory, making future encounters less frequent and the possibility of an impact even more remote.

"Not in the immediate future, certainly, although it's one of a group we keep an eye on because it does cross close to the Earth's orbit from time to time," Yeomans said. "It's just a question of whether the Earth happens to be around."

And it's a good thing Earth won't be in the way Friday. Thought to be a rocky silicate asteroid, 2012 DA14 is moving some eight times faster than a high-velocity rifle bullet. It likely would explode in the atmosphere in an actual collision, but it would still result in a 2.4-megaton blast.

A similar object is believed to have crashed into the atmosphere above Siberia in June 1908, creating an air blast now known as the Tunguska Event that leveled millions of trees over more than 800 square miles.

But impact damage depends in large part on the incoming body's composition. A 150-foot-wide nickel-iron asteroid punched through the atmosphere above Arizona 50,000 years ago and blasted out what is now known as Meteor Crater, a mile-wide crater more than 550 feet deep.

Nickel-iron bodies are relatively rare and while scientists don't yet know the details of 2012 DA14's composition, Yeomans said it's most likely a rocky silicate.

In any case, 2012 DA14 has no chance of hitting the Earth, and, thanks to the expected gravity-induced change in trajectory, it will not pass this close in the foreseeable future.

"Although its size is not well determined, this near-Earth asteroid is thought to be about 45 meters in diameter, it will pass within 17,200 miles of the Earth's surface on Feb. 15," Yeomans told reporters during a briefing. "This asteroid's orbit is so well known, we can say with confidence that even considering its orbital uncertainties, it can pass no closer than 17,100 miles from the Earth's surface. So no Earth impact is possible.

"At the same time, it will pass 5,000 miles inside the ring of communications and weather satellites in geosynchronous orbit. The likelihood of an asteroid colliding with an Earth satellite is extremely remote, but even so we are working with satellite providers to make them aware of the asteroid's path near Earth."

The majority of the solar system's asteroids circle the sun in a doughnut-shaped torus between the orbits of Mars and Jupiter.

Astronomers believe Jupiter's titanic gravity prevented the material from coming together to form a small planet during the birth of the solar system 4.6 billion years ago. The mass of all the known asteroids is comparable to a body less than 1,000 miles in diameter, or about half the size of the moon.

But not all asteroids reside in the main belt between Mars and Jupiter. NASA has identified nearly 10,000 asteroids over the past 15 years, including 2012 DA14, that travel along trajectories carrying them relatively close to Earth.

Out of that population, nearly 1,400 "potentially hazardous asteroids," or PHAs, have been identified to date that could one day pass close enough to Earth to pose a threat. 2012 DA14 is not classified as a PHA.

"This 'potential' to make close Earth approaches does not mean a PHA will impact the Earth," according to NASA's Near Earth Object Program web site. "It only means there is a possibility for such a threat.

"By monitoring these PHAs and updating their orbits as new observations become available, we can better predict the close-approach statistics and thus their Earth-impact threat."

Researchers say the number of known near-Earth asteroids probably represents just 10 percent or so of the actual population.

  • William Harwood

    Bill Harwood has been covering the U.S. space program full-time since 1984, first as Cape Canaveral bureau chief for United Press International and now as a consultant for CBS News. He has covered more than 125 shuttle missions, every interplanetary flight since Voyager 2's flyby of Neptune, and scores of commercial and military launches. Based at the Kennedy Space Center in Florida, Harwood is a devoted amateur astronomer and co-author of "Comm Check: The Final Flight of Shuttle Columbia." You can follow his frequent status updates at the CBS News Space page.

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