This NASA diagram depicting the passage of asteroid 2012 DA14 through the Earth-moon system on Friday.
By Tariq Malik
An asteroid half the size of a football field will buzz close by Earth on Friday, coming closer than many weather satellites, but there is absolutely no chance the space rock will hit the planet, NASA says.
The asteroid 2012 DA14will approach within 17,200 miles (27,000 kilometers) of Earth when it zips by the planet on Friday. It will be 5,000 miles closer than the ring of weather, communications and GPS navigation satellites that orbit the Earth, but it poses no impact threat, NASA scientists assured.
According to detailed observations of the 150-foot (45 meters) 2012 DA14 since its discovery last year, "there is no chance that the asteroid might be on a collision course with Earth," NASA officials said in a statement.
But the space rock encounter will mark the closest-ever known Earth flyby of an asteroid the size of 2012 DA14, with NASA scientists and astronomers around the world preparing to take advantage of the event to take a close look at how asteroids work.
Asteroid 2012 DA14 is about the size of half a football field and will make a close approach to Earth on Friday.
One study in particular seeks to pin down exactly how the asteroid spins on its axis.
"Knowing the direction of spin is essential to accurately predicting its future path, and thus determining just how close it will get to Earth in the coming years," study leader Michael Busch of the National Radio Astronomy Observatory (NRAO) said in a statement.
Busch and his colleagues will use two huge radio telescopes in New Mexico, the Very Large Array and Very Long Baseline Array, along with NASA's Goldstone radar antenna in California in an attempt to determine the direction of asteroid 2012 DA's spin.
The telescopes seek out so-called "speckles" in the radio signals reflected by the asteroid's uneven surface, and then compare which observatory detected the speckles first in order to determine the spin direction.
Knowing an asteroid's spin is key to understanding how a space rock radiates heat from absorbed sunlight over time. That, in turn, can allow astronomers to project how an asteroid's orbit can change over long periods as it circles the sun.
Asteroids, like Earth, have a warmest part of their day, during which time they develop a hotspot that can be observed in infrared light. Later, the asteroid emits the absorbed radiation back out into space, which can serve as a gentle — but firm — jet-like push forward, researchers said.
The phenomenon is called the "Yarkovsky Effect" after the 19th-century Russian engineer I.O. Yarkovsky, who first identified it.
"When the asteroid passes close to the Earth or another large body, its orbit can be changed quickly by the gravitational effect of the larger body, but the Yarkovsky Effect, though smaller, is at work all the time," Busch said.
Alexandra Bolling, NRAO / AUI / NSF
This diagram shows how the Yarkovsky Effect slows an asteroid's orbital motion; opposite rotation direction would speed up the orbital motion. Astronomers around the world are preparing to study the close approach of asteroid 2012 DA14 on Friday.
Asteroid 2012 DA14 was discovered in 2012 by astronomers with the La Sagra Sky Survey at the Astronomical Observatory of Mallorca in Spain. The asteroid will make its closest approach to Earth at 2:24 p.m. EST Friday, at which time it may be visible in telescopes and binoculars to observers in Asia, Australia and Europe, where the local time will be nighttime.
Visit Space.com each day this week for complete coverage of asteroid 2012 DA14 and its Earth flyby.
Editor's note: If you snap a photo of asteroid 2012 DA14 or any other night sky object, and you'd like to share it for a possible story or image gallery, send photos, comments and your name and location to Managing Editor Tariq Malik at email@example.com.
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