Asteroid Raksasa Mendekati Bumi, Berpotensi Tsunami

Astronomers have trained their instruments on a huge asteroid due to cross Earth's path Tuesday, in the closet approach of such an object in a generation. Robert Lee Hotz has details on The News Hub.

Astronomers are tracking an asteroid about the size of an aircraft carrier that on Tuesday will pass by Earth, within the moon's orbit, in the closest approach of such an object in a generation.

The 1,300-foot-wide asteroid, known as 2005 YU55, poses no hazard, experts at NASA's Jet Propulsion Laboratory said.

They are monitoring the spinning space rock by radar as it nears and eventually speeds past Earth at a distance of 201,000 miles. The asteroid is going 29,000 miles per hour, according to astronomers at the University of Arizona.

It is the first time since 1976 that an asteroid has come so close to Earth, and the first time astronomers have ever had this much advance notice.

By astronomers' calculations, the asteroid is expected to make its closest approach to Earth at 6:28 pm EST Tuesday. The asteroid is too dim to be seen with the naked eye and its gravity is too weak to affect tides or earthquake activity, said experts at the National Aeronautics and Space Administration.

Its most important effect may be the adrenaline it has generated this week among the planetary astronomers tracking it through NASA's Deep Space Network antennas, the Arecibo radio-telescope in Puerto Rico and hundreds of telescopes world-wide.

"This is an extraordinary opportunity to look at an extremely important type of asteroid," said Donald K. Yeomans, head of NASA's Near-Earth Object Program Office, which tracks these objects. "A small army of astronomers are pretty excited about it."

Among the oldest objects in the solar system, such carbon-rich asteroids may hold water and important ores, as well as clues to the molecular origins of life on Earth. They also may become humankind's next destination in space, if current plans by NASA for a manned mission to an asteroid come to fruition.

"These objects may one day be the fueling stations and watering holes for interplanetary travel," Dr. Yeomans said.

The solar system harbors millions of asteroids, but only a few are known to cross Earth's path, like the gigantic object that struck the planet some 65 million years ago, part of a chain of events that led to the demise of the dinosaurs. That impact left a crater 110 miles wide in Mexico's Yucatan Peninsula, suggesting the original object was six miles or more in diameter.

By that standard, 2005 YU55 is a medium-size asteroid, among about an estimated 19,500 comparable space rocks between 330 feet and 3,300 feet wide believed to have orbits around the sun intercepting Earth's, according to NASA's most recent tally released in September. Some, like 2005 YU55, are rich in organic chemistry, but many are stony or more metallic. Only about a third of them have been located so far.

The asteroid 2005 YU55 was first detected six years ago and until now, researchers knew little more than its precise orbit. Previous observations suggest it is a fairly symmetrical stone sphere, darker than the color of charcoal, and rotates once every 18 hours.

NASA radar astronomers picked up its track on Friday and were immediately able to narrow its position to within one kilometer—50 times better than their previous best estimate.

"We pinged it," said Marina Brozovic, a planetary radar astronomer who is leading the Jet Propulsion Laboratory's team at NASA's Goldstone radar installation that is following the asteroid. "It's there."

During the next 48 hours or so, the astronomers expect to map the asteroid's surface and refine their knowledge about its orbit enough to predict its precise path well into the future. "We will probably know centuries ahead where it is going to be," said Dr. Brozovic. "We don't want any surprises."

It will be 2028 before another asteroid comes so close to Earth, when the asteroid 2001 WN5 passes at a distance of about 143,000 miles.

The fly-by of 2005 YU55 offers astronomers an opportunity to rehearse their target acquisition and tracking techniques, in the event that an asteroid is ever discovered on a collision course with Earth. "We would like to know more about them in case one was found on an Earth-threatening trajectory," Dr. Yeomans said.

Write to Robert Lee Hotz at sciencejournal@wsj.com