Threats
from Outer Space- Asteroids, Comets and Debris
Remote
telescope Asteroid monitoring!
Asteroids - bits
of pieces left over from the formation of the solar system.
Asteroids range in size from
dust particles to several miles across.
Comets- a
celestial body moving in an orbit about the sun and consisting of a nucleus of
more or less condensed material, accompanied by a tenuous coma pointing away
from the sun.
The first known asteroids were
discovered during the early 19th Century.
These discovered objects orbit
the sun in the main "asteroid belt" which is more like a loose
grouping than a belt, and lies between 2.5 and
There are asteroids all over
the solar system - they are not just confined to the belt itself.
But there was one exceptional
body - it was discovered in 1898 and subsequently named Eros; this was the
first known "near-Earth" - NEO asteroid, and it occasionally makes
relatively close approaches to Earth.
·
One way of asteroids
classification is based upon their relative location and orbit in the solar
system:
|
1.
Amors asteroids |
cross
Mars orbit |
|
2.
Apollos asteroids |
Sometimes called Earth
Grazers; cross Earth's orbit. |
|
3.
Atens asteroids |
orbits lie completely inside
of Earth's orbit |
|
4.
Centaur asteroids |
Lie between 5.5 and |
|
5.
Trojan asteroids |
Asteroids that lie in the
Lagrange 4 and 5 points of some of the planets. |
|
6.
Kuiper Belt Objects
- TNO's |
(Trans-Neptunian Objects) are
asteroids / comets that lie beyond |
Comets and asteroids can be
real players in Earthly events. They carry great amount of
energy, due to their enormous velocity.
Kinetic energy = one-half of
mass times velocity squared, and asteroids and comets typically impact at
between 9 and
Asteroids are too small to be
spherical in shape, they are usually ellipsoids, but some has sporadic shapes
as well.
Asteroids bear the tale of the
violence of the solar system, the larger ones has many sizeable craters on
their surface.
When an asteroid like body
impact a planet, it can carry the energy contained in all the nuclear weapons
ever made – and even more than that.
When the object is large enough (over
The geological record of Earth shows that such
catastrophic collision(s) have occurred in our planets short history. It is
believed that such a catastrophic collision caused the demise of the dinosaurs
about 65 million years ago.
For this reason, there are several asteroid observation programs conducted by astronomers around the globe
in order to warn of any impending collision, and hopefully to make it possible
to take evasive action- if needed.
Such programs involve vigilant observations of
asteroids and near earth objects (NEOs).
·
Bareket observatory and GRAS observatories
participates in such assignments by the contribution of observations and follow
ups of asteroids to the Minor Planet Centre.
·
Asteroids are made of rock and
metal. They are grouped into three categories:
1.
Most asteroids are Stony
(about 92% from the known asteroids).
2.
Iron-Nickel (about 6%
from the known asteroids).
3.
A mixture of the above
two groups (about 2% from the known asteroids).
* An
ideal configuration would be a worldwide network of instruments able to survey
the sky.
Problem is, most asteroids are unknown, which
makes this assurance somewhat less than ironclad. According to one estimate,
1,500 to 2,000 asteroids larger than
The
further out such objects initially formed, the more likely they are to have a
composition including various ices. The Trans-Neptunian's objects are thought
to have a much higher volume of ice than the “Main Belt” objects orbiting
between Mars and Jupiter. Trans Neptunian's Objects are considered asteroids.
However, when they are drawn into an orbit closer to the Sun, heat from the Sun
begins to create the characteristic coma of a comet. This was seem when the Centaur,
2060 Chiron, previously classified as an asteroid, drew closer to the Sun at
perihelion and began to develop a comet’s coma.
Practical
observing methods:
·
Follow up and recovery ;
Astrometry - Programs such as Spacewatch and LINEAR are primarily
search-and-discovery efforts; they are primarily oriented towards the discovery
of previously-undiscovered objects. Follow-up observations, such as positional
measurements which are essential to the calculation of a reliable orbit, are
usually left to other entities. This type of work may not be as
"glamorous" as the discovery efforts but it is these follow-up
observations that may extend over the weeks and months following the actual
discoveries that allow any hope of tracking these objects down in the future.
the recovery of these objects during the periods when they are observable is
absolutely essential if we wish to calculate orbits that will allow us to keep
track of them in the future.
·
. Record
keeping - Positional data and orbital information for asteroids are
maintained by the International Astronomical Union's
·
Rotational periods ;
Photometry light curves - A light curve is a chart showing variation in magnitude (y
axis) with time (x axis).
- CALL Guide to Minor Planet Photometry
Collaborative Asteroid Light curve Link (CALL)
purpose is to allow those engaged in determining asteroid light curve
parameters to coordinate their efforts so that the best use of observing time
can be made. A very useful guide in getting started with measuring
asteroid light curves can be accessed here.
·
Comets -
being diffuse objects with measurable apparent size (as opposed to the point
like stellar appearance exhibited by asteroids) are, in general, easier to
detect than are asteroids. Almost all of the short period. There are no threats
from any of these objects within the near future. Space watch program should
prove somewhat effective in detecting long-period comets while still relatively
far from the sun and Earth, but this is an endeavor where eternal vigilance
will continue to be necessary for the foreseeable future.
