[meteorite-list] Small Near-Earth Asteroids Pose More Imminent Threat

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:17:39 2004
Message-ID: <200312041629.IAA00718_at_zagami.jpl.nasa.gov>

http://www.usatoday.com/news/science/2003-12-02-asteroids-usat_x.htm

Small near-Earth asteroids pose more imminent threat
By Dan Vergano
USA TODAY
December 2, 2003

Bad things can come in little
packages, astronomers warn. So after a decade of searching for
massive asteroids, they are turning to the threat posed by
smaller, more common space rocks closer to Earth.

Most worries about impacts from space have centered on objects
more than half a mile across. They are thought to smack into
Earth every few million years, some with such force they trigger
mass extinctions like the one that ended the age of the dinosaurs
65 million years ago.

But a recently released NASA "Near-Earth Object Search"
report scheduled for discussion at the American Geophysical
Union meeting next week calls for better observation of smaller
asteroids.

These rocks wouldn't trigger the global devastation of their larger
brethren, but their impacts could still cause massive local
damage, chiefly from tidal waves.

Because asteroids about one-twelfth of a mile across hit about
once every 1,000 years, they are a more imminent threat than
giant impacts, the report warns. It was written by a team of
scientists headed by space-surveillance expert Grant Stokes of
MIT's Lincoln Laboratory.

Asteroids come and go by Earth. In August, one nearly
three-quarters of a mile wide named QQ47 received considerable
media attention because of reports that it might hit Earth in 2014.
But like many asteroid scares in recent years, astronomers
quickly dismissed any impact possibility after more observation.

But sometimes impacts happen. Most recently, an asteroid
perhaps 200 feet wide blasted the Tunguska region of Siberia in
1908, flattening almost 800 square miles of forest.

Five years ago, NASA began looking for larger asteroids and
comets, hoping to detect 90% of them by 2009. About 60% of the
estimated 1,200 large objects traveling near Earth have already
been discovered.

Among smaller asteroids nearby, perhaps half a million are
"potentially hazardous," the report says. It suggests:

* Tidal wave deaths from an ocean impact would be lower than
  past predictions, a few hundred people perhaps, because
  evacuations should lessen the risk.

* Searches for small comets should be bypassed, because they
  represent only 1% of the impact risk.

* A seven- to 20-year search for nearby small asteroids that
  pose about 90% of the impact risk would cost under $400 million.

A mixture of ground telescopes and space probes would fit the
criteria for the search recommended by the report. A satellite
trailing near Venus to watch for sun-grazing asteroids combined
with ground-based telescopes offers a quicker, but slightly more
expensive, approach than relying on an Earth-orbiting telescope
for asteroid warnings.
Received on Thu 04 Dec 2003 11:29:13 AM PST