- WASHINGTON (Reuters) - Two
hefty asteroids passed close to Earth on Wednesday, with at least five
more set to swing near by January's end, but none are dinosaur-killers,
scientists who track them said.
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- One of Wednesday's close-approaching asteroids measured
between .6 and 1.8 miles in diameter, a big enough space rock to cause
catastrophe if it collided with Earth.
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- But asteroid 7341 1991 VK got no closer than 7 million
miles, nearly 24 times the distance from the Earth to the Moon.
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- The other asteroid, 2002 AO11, came much nearer -- about
3 million miles -- though at a relatively petite 246 feet across, posed
no threat to Earth.
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- Both were considered near-Earth objects (NEOs) but not
necessarily potentially hazardous asteroids (PHAs).
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- There are at least five more fairly big asteroids in
line to get close to Earth's orbit between now and Jan. 29, according to
NASA's Near Earth Object Program.
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- There was some mild consternation over a PHA known as
2001 YB5, a 1,000-foot wide asteroid that got within 500,000 miles of Earth
last week, having come to astronomers' attention just after
Christmas.
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- "In cosmic terms, it is close," said Don
Yeomans,
manager of NASA's Near Earth Object Office at the Jet Propulsion Laboratory
in California. "There was never any chance of this hitting. It's sort
of nature's wake-up call, saying there are a whole bunch of these things
out there -- get on the stick!"
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- It is Yeomans' job to calculate the orbits of NEOs and
PHAs once they are detected, and detection of these big asteroids has
mushroomed
over the last decade, according to Steve Pravdo, a key investigator at
NASA's Near Earth Asteroid Tracking project.
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- 564 BIG SPACE ROCKS
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- The project watches for asteroids .6 miles or more across
that have the potential to wreak havoc on Earth if they hit. Of the
approximately
1,200 big dangerous asteroids believed to exist, scientists have detected
564. The vast majority of those -- 471 -- have been discovered since 1990,
Pravdo said in a telephone interview.
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- If one of these struck Earth, Pravdo said, it would be
what they call "a continent embarrasser."
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- "If it landed in a metropolitan area, bye bye to
that area ... (it) could take care of a continent, but it wouldn't change
the ecosystem the way the one that killed the dinosaurs did."
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- Many scientists believe that an asteroid perhaps 3 miles
across wiped out the dinosaurs and many other species when it crashed to
Earth 65 million years ago.
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- Pravdo said there was at least one dinosaur-killer-sized
rock among the asteroids in the project's catalog: 2001 OG108, with a
diameter
of nearly 7 miles, about twice as big as the one that doomed the
dinos.
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- But it is not considered hazardous, since it has no
potential
to come in contact with Earth in the foreseeable future, Pravdo said. It
does cross Earth's orbit, but is not expected to get close to the planet,
he said.
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- The chances of being killed by an asteroid are about
the same as the chances of dying in a commercial plane crash, not because
serious asteroid collisions are common but because their effects would
be so far-reaching.
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- The worst crashes are capable of causing global climatic
catastrophe, kicking up a debris cloud that could ultimately lower
temperatures
and kill plants, animals and people. These occur perhaps once every 100,000
years.
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- Most asteroids lie in a wide belt between the orbits
of Mars and Jupiter, but Yeomans and Pravdo keep watch on those near Earth.
The National Aeronautics and Space Administration and other astronomic
organizations aim to identify all the NEOs by 2008.
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- Copyright © 2002 Reuters Limited. All rights
reserved.
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