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Asteroid picture: 2005 YU55 as seen by radar.

A radar image of asteroid 2005 YU55 taken last April at Arecibo Observatory.

Image courtesy Arecibo/Cornell/NASA

Ker Than

for National Geographic News

Published November 7, 2011

An asteroid the size of an aircraft carrier will make a close pass by Earth tomorrow, and astronomers worldwide are ready and waiting to catch the sky show.

Dubbed 2005 YU55, the asteroid's closest approach to our planet will occur at 6:28 p.m. ET on Tuesday.

That's when the 1,300-foot-wide (400-meter-wide), roughly spherical space rock will fly within about 197,000 miles (317,000 kilometers)—closer than the moon's orbit.

The last time an asteroid this big approached so close to Earth was in 1976. (Read about a school bus-size asteroid that buzzed Earth in June.)

This asteroid will be so close, in fact, that amateur astronomers—especially those in North America and western Europe—will be able to see it with moderately powerful telescopes.

The asteroid will streak eastward across several constellations, from Aquila to Pegasus, in just under ten hours.

"If you have a mirror telescope, you'll need a mirror that's bigger than about 6 inches [15.2 centimeters] to see it," said Jon Giorgini, a senior analyst with the Solar System Dynamics Group at NASA's Jet Propulsion Laboratory in Pasadena, California.

Many telescopes today have motors that "cancel out the rotation of the Earth, so they rotate at a rate that compensates for the spinning of the Earth, so they can remain fixed on a patch of sky," Giorgini added.

But 2005 YU55 will be "moving pretty rapidly, so you'll need a faster than usual motor to keep up."

(Get more tips on how to see 2005 YU55, including a sky chart with the asteroid's path.)

Asteroid Flyby a Boon to Astronomers

Professional astronomers have also been interested in 2005 YU55 since it was discovered nearly six years ago by Robert McMillan, using the Spacewatch telescope at Steward Observatory in Arizona.

(Related: "Trojan Asteroid Found Sharing Earth's Orbit—A First.")

Until now, however, the relatively dark asteroid has been too far away for astronomers to gather much data.

"Its orbit goes out a little past the orbit of Mars, and it swoops in again past the orbit of Venus. So the last year and a half, it's been too far away," for detailed observations, Giorgini said.

"It's also a very dark object—it only reflects a little less than 10 percent of the light" from the sun.

To take advantage of the close flyby, NASA scientists have been tracking the asteroid with the agency's Deep Space Network in Goldstone, California, since November 4. The giant radio telescope at Arecibo Observatory in Puerto Rico will also begin following the asteroid on November 8.

"[Scientists] are going to be studying it thermally to try and figure out how it radiates heat, which will tell them something about the material properties of the asteroid," Giorgini explained.

"We're also going to be looking at it with radar, and that's going to tell us about its shape and the way it spins," he said.

"We'll then be able to combine all this information together to get a good idea of what this object might be made of and how it's constructed."

Near-Earth Asteroid Not a Threat

The asteroid's orbit takes it into the vicinity of Earth regularly, but the planet isn't in imminent danger: The 2011 approach will be the closest for at least 200 years, scientists say.

(Related: "NASA to Visit Asteroid Predicted to Hit Earth?")

While it's possible that a manned mission might one day visit 2005 YU55 during one of its near-Earth approaches, there are better candidates—such as the near-Earth asteroid 2000 EA14—that are easier to reach, Giorgini said.

The orbit of 2005 YU55 "is different enough [relative to Earth's], so it takes a bit more energy to get to it," he said.

"When you're planning a manned mission, you want something that takes the least amount of energy, and this takes just a tiny bit more than other objects."

Also see related pictures: NASA Lands on Underwater "Asteroid" >>

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