Scientists at JPL are keeping track of an asteroid as big as an aircraft carrier as it zips by Earth on Tuesday in the closest encounter by such a massive space rock in more than three decades.
By Conan Nolan and Julie Brayton | KNBC-TV Los Angeles
Tuesday, Nov 8, 2011 | Updated 6:22 PM PST
An asteroid as big as an aircraft carrier swept past Earth on Tuesday in the closest encounter by such a massive space rock in more than three decades.Scientists ruled out any chance of a collision, but turned their telescopes skyward to learn more about the object known as 2005 YU55.
Its closest approach to Earth was pegged at a distance of 202,000 miles at 3:28 p.m. PST. That turned out to be just inside the moon's orbit.
The average distance between Earth and the moon is 239,000 miles.
"The orbit of this asteroid extends as far as Mars, and inwards as far as Venus," according to Dr. Paul Chodas, of JPL. "So this asteroid can actually encounter three planets. We have to keep track of it very carefully because the gravity of all three planets can be significant in it's orbit."
The last time a large cosmic interloper came that close to earth was in 1976 and it won't happen again until 2028.
Scientists at NASA's Deep Space Network in the California desert tracked the quarter-mile-wide asteroid since last week as it approached from the direction of the sun at 29,000 mph.
Astronomers and amateur skygazers around the world kept watch, too, and there will still be plenty of opportunities to see if for the next two days.
"It'll be moving at a fair clip. Because it's so close and moving so quickly, you'll be able to see it move against the star background," says Dr. Chodas.
If an asteroid that size would hit, Purdue University Professor Jay Melosh calculated the consequences.
The impact would carve a crater four miles across and 1,700 feet deep. And if it slammed into the ocean, it would trigger 70-foot-high tsunami waves.
Since its discovery six years ago, scientists have been monitoring the spherical, coal-colored asteroid as it slowly spins through space and were confident it posed no danger.
Asteroids are leftovers from the formation of the solar system some 4.5 billion years ago. Scientists believe their growth was stunted by Jupiter's gravitational pull and never had the chance to become full-fledged planets. Pieces of asteroids periodically break off and make fiery plunges through the atmosphere as meteorites.
Don Yeomans, who heads NASA's Near Earth Object Program, said 2005 YU55 is the type of asteroid that humans may want to visit because it contains carbon-based materials and possibly frozen water.
With the space shuttle program retired, the Obama administration wants astronauts to land on an asteroid as a stepping stone to Mars.
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