[meteorite-list] Two Hefty Asteroids Pass Close to Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:55:47 2004
Message-ID: <200201170111.RAA15571_at_zagami.jpl.nasa.gov>

http://www.reuters.com/news_article.jhtml?type=search&StoryID=520982

Two Hefty Asteroids Pass Close to Earth
January 16, 2002

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.

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.

But asteroid 7341 1991 VK got no closer than 7 million miles, nearly 24
times the distance from the Earth to the Moon.

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.

Both were considered near-Earth objects (NEOs) but not necessarily
potentially hazardous asteroids (PHAs).

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.

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.

"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!"

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.

564 BIG SPACE ROCKS

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.

If one of these struck Earth, Pravdo said, it would be what they call "a
continent embarrasser."

"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."

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.

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.

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.

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.

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.

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.
Received on Wed 16 Jan 2002 08:11:10 PM PST