From: LARRY KLAES (ljk4@msn.com)
Date: Fri Apr 05 2002 - 11:05:00 PST
----- Original Message -----
From: baalke@jpl.nasa.gov
Sent: Friday, April 05, 2002 2:04 PM
To: undisclosed-recipients:;
Subject: Hitchhiker's Guide to an Asteroid
http://science.nasa.gov/headlines/y2002/05apr_hitchhiker.htm
Hitchhiker's Guide to an Asteroid
NASA Science News
Learning what near-Earth asteroids are made of and how they're put together
is simply prudent. NASA's NEAR spacecraft did just that when it landed on
one in 2001.
April 5, 2002: When NASA's Near Earth Asteroid Rendezvous (NEAR) Shoemaker
spacecraft visited the asteroid 433 Eros last year, no one was on board. It
was strictly excitement from a distance, exploring the potato-shaped
20-by-8-by-8-mile worldlet through robotic eyes.
But what if you could have hitched a ride on the automobile-sized spacecraft
from its launch in February 1996 through its first-ever landing on an
asteroid? What would you have seen--and discovered?
In early 2000, after nearly four years en route, you would have been excited
to be approaching Eros at last--slowly enough to be captured into orbit
despite the relatively small body's weak gravity. Then you would have had a
year to examine the curious object from all angles, both in darkness and in
sunlight, and from distances ranging from 200 miles down to as close as 22
miles. Lastly, in a thrilling four-hour finale on February 14, 2001, you
would have clung to NEAR as it oh-so-gently settled down onto the very
surface of Eros at merely walking speed, to rest on the tips of two solar
panels and the bottom edge of the spacecraft's body--a deliberately planned
interplanetary kiss on Valentine's Day with an asteroid named for the god of
love.
Why 433 Eros? As some asteroids in the main belt between Mars and Jupiter
are hundreds of miles across, wouldn't they have made more interesting
targets?
Bigger, yes, certainly. More interesting? Perhaps not.
433 Eros intrigued NEAR scientists for several reasons.
First, for figuring out what asteroids are made of, smaller is better than
bigger. Astronomers have long speculated that asteroids are remnants left
over from the original creation of the solar system more than 4.5 billion
years ago. But just what was that primoridal material? On Earth, because of
eons of volcanism and weathering, it's impossible to find an unchanged rock
that old. Asteroids the size of Eros, however, never got big enough to melt
and reform, so they are nearly pristine samples of the most primitive stuff
in the solar system.
And what ancient secrets might you have seen on Eros as you swooped down
close to its surface on NEAR?
Well, Eros may be ancient and geologically unchanged, but it also looks
startlingly weathered. Instead of sharp edges where it could have broken off
a larger body or been struck by another asteroid, peaks and crater rims are
rounded and worn--perhaps by a process called "gardening," in which small
impacts from interplanetary dust and gravel over millions of years wear away
sharp projections. Its surface is littered with thousands of loose boulders
the size of houses--most of them apparently having fallen back to the
surface after having been scoured out of the largest impact crater on Eros
(some 5 miles across).
Moreover, Eros is peppered with smaller craters partially filled with flat
ponds of fine bluish dust--dust that appears to settle in the craters as
smoothly as if it were a fluid. Both loose boulders and dust ponds are
astonishing to find on a body whose gravity is so weak that a 200-lb
basketball player would weigh only 2 ounces and would risk launching himself
into orbit with one good jump shot!
Another reason NASA targeted Eros is that, small as it is, it is actually
the second largest of a family of asteroids that can approach within 121
million miles of the sun--that is, possibly within a few million miles of
Earth. Aside from the Moon, such near-Earth asteroids (NEAs) are our closest
neighbors in the solar system--so it's just plain neighborly to go calling
and learn a bit more about them!
Finding out all we can about near-Earth asteroids is prudent. Although Eros
does not come close enough to Earth for a collision, other asteroids in
different orbits might. Indeed, many space rocks have struck Earth in the
distant past. Even now 40 to 100 tons of smaller interplanetary debris and
dust fall into Earth's atmosphere daily. If a rock larger than two-thirds of
a mile (1 kilometer) in diameter should slam into Earth, tidal waves,
firestorms, and other traumas could spell disaster for civilization and
possibly even for all of life on our planet. Right now, one NASA program is
scanning the heavens to inventory all near-Earth asteroids; so far, the
total is more than 1800, but only 400 or so are rated as "potentially
hazardous."
That's another reason for interest in visiting Eros--to find out how it (and
other NEAs) are constructed. Are they solid rock? Or are they--like many
mountains on Earth--more like compacted piles of rubble? To anyone
considering either redirecting an Earth-approaching asteroid into a
different (safer for Earth) orbit or blowing it to smithereens with a
thermonuclear warhead, it's essential to know where best to give the
asteroid an effective push or whether its fragments will disperse as much as
you hope.
The existence on 433 Eros of craters--and of square-shaped craters at
that--seem to suggest the asteroid is one solid body of fractured rock, of
one uniform composition similar to the most ancient known meteorites (called
chondrites) of material probably older than Earth. At least, that's the
prevailing view of most scientists since having seen it close-up through
NEAR's cameras and having probed it with NEAR's gamma-ray spectrometer after
the craft landed.
Perhaps such solid rock might it make a good bedrock foundation for a mining
operation.... (Maybe as the first squatter on Eros, NEAR should file a
prospector's claim.) Could there be ice frozen in the fractures? Could
asteroids be refueling stations and sources of raw materials for colonies in
the inner solar system? NEAR taught us a great deal, yet many mysteries
remain.
Oh, just one last hitchhiker's question. Which way to get back to Earth?
This archive was generated by hypermail 2.1.2 : Fri Apr 05 2002 - 11:12:24 PST