[meteorite-list] Radar Love: Asteroid Detection and Science

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 19 Dec 2006 17:01:20 -0800 (PST)
Message-ID: <200612200101.RAA00091_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/features.cfm?feature=1253

Radar Love: Asteroid Detection and Science
December 19, 2006

They are the celestial equivalent of sonograms. But their hazy outlines
and ghostly features do not document the in-vivo development of a future
taxpayer. Instead, they chronicle the exo-planetary comings-and-goings
of some of Earth's least known, most nomadic, and at times most
impactful neighbors.

They are radar echoes that are bounced off of asteroids. Scientists from
NASA's Jet Propulsion Laboratory and around the world rely on their
ethereal images to tell some out-of-this-world tales of near-Earth objects.

"The standard ground-based tools for asteroid science require a night's
sky, and what you come away with in the end is an image of a dot," said
JPL radar astronomer Dr. Steve Ostro. "With radar astronomy, the sky at
high noon is just as inviting as that at midnight, and without launching
a full-blown space mission we can actually get valuable information
about the physical makeup of these objects."

In some respects, radar astronomy utilizes the same technology as your
microwave oven. But do not bother to haul your glorified croissant
warmer outside -- it will just confuse the neighbors. Radar astronomy
employs the world's most massive dish-shaped antennas, which beam
directed microwave signals at their targets, which can be as close as
our moon and as far away as the moons of Saturn. These pulses bounce off
the target, and the resulting "echo" is collected and precisely
collated. The results can be astounding.

"The closer the target, the better the echo," said Ostro. "From them we
can generate detailed three-dimensional models of the object, define its
rotation precisely and get a good idea of its internal density
distribution. You can even make out surface features. A good echo can
give us a spatial resolution finer than 10 meters."

Radar astronomy has detected echoes from over 190 near-Earth asteroids
to date and has found that, like snowflakes, no two are the same. The
returning echoes have revealed both stony and metallic objects, some
flying through the cold, dark reaches of space alone, while others have
their own satellites. The data indicate that some asteroids have a very
smooth surface, while others have very coarse terrain. And finally,
their shapes are virtually anything that can be imagined.

One thing that does not have to be imagined is radar astronomy's ability
to nail down the location of an object in time and space. This
invaluable capability came in handy in the winter of 2004 when JPL's
Near-Earth Object office was looking for a potentially hazardous
asteroid called Apophis.

Discovered by astronomers using optical telescopes, Apophis quickly drew
the interest of the near-Earth object monitoring community when its
initial orbital plots indicated there was a possibility the
1,300-foot-wide chunk of space rock could impact Earth in 2029. The
Near-Earth Object office knew what was needed was more detailed
information about Apophis' location, which they could then use to plot
out a more accurate orbit.

Under the watchful eye of Ostro and three other radar astronomers,
microwaves from the Arecibo Observatory in Puerto Rico reached out and
touched asteroid Apophis on Jan. 27, 29, and 30, 2005. The Arecibo data
significantly improved the asteroid's orbital estimate, ruling out a
potential Earth collision in 2029.

The 1,000-foot diameter Arecibo telescope is one of only two places in
the world where radar astronomy is effectively performed. The other is
at the 70-meter Goldstone antenna in California's Mojave Desert. The two
instruments are complementary. The Arecibo radar is not fully steerable
(while Goldstone is), but it is 30 times more sensitive. Together they
make a formidable asteroid reconnaissance team.

The future of radar astronomy may be just as amazing as some of the
images and shape models of nearby space objects that its practitioners
have already obtained. There is new technology in the pipeline that will
allow imaging of surface features with up to four times more detail than
what exists today. And then there are proposals on the table for a
potential space mission to a near-Earth asteroid. Candidate asteroids
for said mission will need to be pre-approved via detail scientific
analysis. The kind of scientific analysis you can only get with radar
astronomy.

Media contact: DC Agle/JPL
818-393-9011
Received on Tue 19 Dec 2006 08:01:20 PM PST