[meteorite-list] JPL Uses Radar To Track Asteroids That Could One Day Threaten Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:50:29 2004
Message-ID: <200204221715.KAA01631_at_zagami.jpl.nasa.gov>

http://www.ocregister.com/news/huntasteroids00422cci.shtml

Keeping asteroids' distance

JPL uses radar to track the celestial objects that could one day threaten
Earth.

BY GARY ROBBINS
The Orange County Register
April 22, 2002

An odd little asteroid will reveal hints about the origins of the solar
system today simply by reflecting radar signals back to an antenna in the
Mojave Desert.

It's no small trick. But scientists can use the return signals to create
pictures of asteroids. In this case, they're looking at 1999 GU3, a piece of
celestial detritus that dates to when the planets formed.

The size, shape and condition of "GU3" will give scientists clues about how
some primordial material coalesced into planets, why some didn't, and how
such worlds as Mars and Earth have evolved in the ether of space.

GU3's message is going to be read by scientists at the Jet Propulsion
Laboratory in Pasadena. JPL has become the world leader in using radar
antennas to create detailed images of asteroids, especially those worrisome
ones known as "Earth-crossers," objects that intersect our orbit. There may
be 300,000 of them the size of Anaheim's Edison Field.

Scientists are able to determine the size, shape, speed, orbit and rotation
of asteroids by how fast radar signals reflect off various parts of the
object to antennas in California or Puerto Rico. The strength of the signal
also plays a role.

JPL's findings are showing asteroids to be stranger than many of the
disaster movies made about them.

"Ten years ago most scientists thought of asteroids as whirling rocks," said
Don Yeomans, a senior scientist at JPL. "Now we know they're exotic. Some
have water. Some don't. Some are almost all metal. Others are just rock. One
is shaped like a dog bone. Another looks like a banana."

JPL and its collaborators also recently announced that it's fairly common
for asteroids to have moons. That was just a theory a few years ago. GU3
doesn't have a companion. But it takes nine days for the rock to rotate
once, making it an oddball. Most asteroids rotate in a matter of hours.

Fear and curiosity are responsible for many of the latest insights.

In 1998, the U.S. House of Representatives instructed the National
Aeronautics and Space Administration to find, follow and characterize 90
percent of all near-Earth asteroids (NEAs) within 10 years. NEAs are
generally defined as asteroids a half-mile or wider that periodically pass
within 30 million miles of Earth.

The reason for the census: to find out if any asteroids could hit Earth and
produce a catastrophe.

The idea is to give humans enough time to find a way to destroy or deflect
potentially damaging objects. JPL is a major player in the project because
it's a NASA center with a masterful record of interacting with objects in
space.

The project gained urgency in January when an asteroid almost as long as the
Huntington Beach Pier came within 518,000 miles of Earth. It had been
discovered only a month earlier by a team led by JPL's Eleanor Helin.

No one knows exactly know many NEAs exist. NASA has officially catalogued
558 asteroids that are at least a half-mile wide. But scientists say that
number probably represents only half the NEAs.

Researchers use optical telescopes to find the NEAs. And they're getting
better at locating them due to improved technology. But many of the most
interesting research has involved radar antennas.

JPL used radar to make an unprecedented long-term prediction: there's a 1 in
300 chance that asteroid 1950 DA - which is about 4,000 feet in diameter --
will hit Earth on March 16, 2880.

To watch for somewhat shorter-term threats, JPL inaugurated Sentry on March
12. It's an automated computer program that evaluates whether any known NEA
has a chance of hitting Earth within the next 100 years.

"This is a magic age in the exploration of asteroids," says Steve Ostro, a
JPL astronomer collaborating with colleague Lance Benner in studying GU3.

"Radar lets us refine orbits and make detailed images of what are
essentially individual worlds. There's no preferred shape or size. We just
never know what we're going to see out there."

That means that Ostro could be in for a surprise today. Arecibo Observatory
in Puerto Rico used its radar antenna to bounce signals off GU3. More
signals are being sent today by the Goldstone Solar System Radar near
Barstow.

The key to success is pinpoint accuracy. Today's signal from Goldstone must
hit a roughly 1,300-foot-wide asteroid that's more than 7.5 million miles
from Earth, traveling about 36,000 mph.

GU3 is one of only 179 asteroids studied with radar.

"Everything about an asteroid - its spin, how much it heats up, what it's
made of - can affect its path and whether it hits Earth," said Jon Giorgini
, another JPL researcher. "We need to know more about the physical
properties of asteroids."

JPL's Helin agrees.

"I feel more worried now than I did when I started this work," said Helin,
who began studying asteroids in 1969. "We've long known that something can
hit us. But we're not prepared to deal with it."
Received on Mon 22 Apr 2002 01:15:53 PM PDT