Near Earth Objects


What are NEOs? Where do they come from? Do they pose any real threat to
Earth? Can they provide viable space resources? All of these questions are now
under investigation by planetary scientist. There are two highly recognized
research programs that I will discuss with you. The Spaceguard program is
sponsored and run by NASA Ames Space Science Division: Asteroid and Comet Impact
Hazard. Also under the direction of Dr. Tom Gehrels the University of Arizona
has the Spacewatch program.
NEOs can be either asteroid or comets. Ninety percent of the
information that I came across discussed asteroids. Therefore, I will
concentrate on asteroids alone. I\'m not fully knowledgeable on the subject but
I did learn a great deal.
What are NEOs? The "Webster\'s New World Dictionary" states, "Any of the
small planets between Mars and Jupiter". The "Funk and Wagnalls Encyclopedia
from Infopedia" states, "One of the many small or minor planets that are members
of the solar system and that move in elliptical orbits primarily between the
orbits of Mars and Jupiter".
Where dot they come from? The NEOs are small objects (<7 miles) with a
range of compositions spanning all common asteroid types. They are derived from
a mixture of main-belt collisional fragments and burned-out short-period comets.
According to Dr. Tom Gehrels of the University of Arizona Spacewatch program,
"The total number of NEOs over 100 meters is estimated to be about 100,000, with
150 or so currently known".
Do they pose any real threat to Earth? The Earth orbits the Sun in sort
of a cosmic shooting gallery, subject to impacts from asteroids. It is only
fairly recent that we have come to appreciate that these impacts by asteroids
pose a significant hazard to life and property. Although the annual probability
of the Earth being struck by a large asteroid is extremely small, the
consequences of such a collision are so devastating that it is prudent to assess
the nature of the threat and prepare to deal with it.
Studies have shown that the risk from a cosmic impact increases with the
size of the projectile. The greatest risk is associated with objects large
enough to perturb the Earth\'s climate on a global scale by injecting large
quantities of dust into the stratosphere. Such an event could depress
temperatures around the globe, leading to massive loss of food crops and
possible breakdown of society. Global catastrophes are qualitatively different
from other more common hazards that we face (except nuclear war), because of
their potential effect on the entire planet and its population.
Various studies have suggested that the minimum mass impacting body to
produce such global consequences is several ten of billions of tons, resulting
in a groundburst explosion with energy in the vicinity if a million megatons of
TNT. The diameter for Earth-crossing asteroids are between 1 3/5 and 3 1/4
miles. Smaller objects (down to 32 feet in diameter) can cause severe local
damage but pose no global threat.
According to Spaceguard, "Of approximately 200 Earth-crossing asteroids,
fewer that 200 have actually been discovered. At present no asteroid is known
to be on a collision course with the Earth. David Morrison of the NASA
Spaceguard Research Center states, "The chances of a collision within the next
century with an object 1 3/5 mile in diameter or more are very small (less than
1 in a 100). But, such a collision is possible and could happen at any time.
If we did have sufficient warning, however, the incoming object could be
deflected or destroyed". Cosmic impacts are the only known natural disaster
that could be avoided entirely by the appropriate application of space
technology.
The Spacewatch telescope located on Kitt Peak is used to survey for
moving objects, including asteroids whose orbits approach or cross the orbit of
the Earth. Among these are asteroids that may someday be used as sources of raw
materials. Spacewatch uses a Charg-Coupled Device or (CCD) and an automated
computer program to discover NEOs.
\'The Spacewatch Observatory has already detected one of the smallest
asteroids known, and also the one that passed very close to Earth, the Apollo
asteroid 1991 BA. The semi-automatic Spacewatch system at the University of
Arizona has considerably increased the discovery rate, and will have profound
consequences on the utility of NEOs as near-Earth space resources.

Category: Science