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Asteroid Gaspra:
Asteroid Toutatis:
Comet:
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(AIS 97/04/25) There are mountains larger than the Mount Everest. These mountains are barely noticeable because most of them have a dark color and are drifting in comparatively great distances through the space of our solar system. They are called asteroids, stone and metallic bodies that are left during the development of planets in the solar system. Asteroids have sizes between the size of a football and a few hundred kilometers (100 km = 62 miles). Asteroids are not known for a long time. The first asteroid was discovered 1801. This was possible due the progress in development of telescopes and the spreading engagement with space. In contrast to asteroids are comets known for a long time to all cultures. These bodies of ice and stone with their long shinning tails are easy to detect even when they are far away. Often their appearance has been interpreted as a sign of heaven and the account has been passed on from generation to generation. The asteroid in contrast, even one of considerable size, would have been detected only in the past if it flew burning brightly through the higher layers of the atmosphere or if it suddenly hit the ground. But even then, people would not have known what it was. Suddenly an earthquake, extensive forest fires, a spring tide, that would have been only some of the many inexplicable hazards people have to deal with in the past. But we know today that asteroids of various sizes have struck the Earth. An asteroid with a diameter of around 12 km struck the Earth 65 million years ago at a point that is now the Yucatan peninsula of Mexico. Half of the Earth's species were extinguished on account of this event and its consequences on the Earth ecosystem and climate system. Today there is a 180 km (112 miles) wide crater. Another crater is the Ries crater in Bavaria/Germany with a diameter of around 25 km caused by an 1.5 km asteroid or comet. Well known is the 'Meteor Crater' in Northern Arizona. It is estimated that a 50 meter metallic asteroid has hit there around 50.000 years ago, leaving a crater 1.2 km wide and 200 m (650 ft.) deep. More than 100 impact crater on Earth are known today. Often these craters are difficult to find due erosion, but are recognizable because of the shock marks on the stones and the minerals in that area. When we look up to the moon we can see it spotted with big craters. The absence of an atmosphere and the resulting lack of erosion preserves its craters. Also other planets and moons of the solar system show the marks of asteroid impacts. Most asteroids are located in the main belt, a ring of asteroids between the orbits of Mars and Jupiter with the Sun in the middle of the ring. The main belt is around 2 astronomical units away from the Sun and around 2 astronomical units broad (Astronomical Unit = Distance Earth - Sun = 150.000.000 km = 93.000.000 miles). The nine planets of the solar system and the main belt are not wildly distributed in space. They move all more or less in a plane and in the same direction, like runners on parallel tracks around the stadium. Occasionally asteroids collide within the main belt or their orbits are disturbed by gravitational forces from Jupiter which bring them on a new course. It is likely that such a body remains in the plane of the solar system and is pulled toward the Sun by its strong gravity field. Such an asteroid might cross the orbit of the Earth. Beside the main belt asteroids there are many others with orbits closer to Earth and also quite a lot are crossing the Earth's orbit. Asteroids called Amors cross Mars' orbit but do not reach the orbit of the Earth. Apollos are asteroids that cross Earth's orbits in periods more than a year. Atens are asteroids which need for their Earth crossing orbits less than a year. The danger of a large asteroid hitting the Earth is not part of our daily consciousness of dangers to be dealt with. And that is reasonable to some point, because this danger is beyond our common experience and the chances for an individual to die by a car accident or disease are much higher. But the consequences if Earth is hit by a big asteroid or comet are grave. The effects will not only be a misfortune for some individuals but it will affect whole cultures. Not only some persons, but also all their relatives will be gone at the same time. Whole countries will probably vanish, their languages, achievements and cultural peculiarities may disappear forever in a matter of some moments.
A supposed spherical asteroid with a diameter of 10 km (6.2 miles)
and a consistence of three parts stone and one part iron with a rather
moderate entry velocity of 20 km/sec (12.4 miles/sec)
would have a kinetic impact energy on the whole earth system
(atmosphere and globe) of approximately 8.378 E23 Joule.
That is an energy equivalent of around 9.500.000.000 hiroshima bombs or
200.000.000 megatons TNT.
Occurrences like the comet fragments chain 'Shoemaker-Levy 9' discovered
1993 and hit Jupiter 1994 show us that the orbits of many bodies in
the solar system have not settled to stable orbits in the last
million years.
Some of the fragments of the comet Shoemaker-Levy 9,
of estimated sizes between 500 m (1600 ft.) and 2 km (1.25 miles), have
punched holes up to Earth's diameter in Jupiter's upper atmospheric layers.
A big explosion in the year 1908 in the barely populated taiga of Tunguska/Siberia
is said to be caused by a little fragment of a comet that exploded high above
the ground, devastating forest and vegetation in an area of around 2000 sq km.
Asteroid Toutatis, size 4.6x2.4x1.9 km (2.85x1.5x1.2 miles) and
discovered 1989, passed the Earth 1992 in a distance of around 3.200.000 km
(2.000.000 miles). Toutatis has an orbit which is difficult to predict because
he has a tumbling rotation, but he will pass the Earth in the year 2004 in
a distance four times the distance Earth-Moon,
which is pretty near on a space scale.
There is a growing awareness of the possible danger of a collision with an
asteroid or comet. Several programs like the
Near-Earth Asteroid Tracking program
or the Spacewatch project (link check, exchanged with working page)
try to catalog all asteroids and find out their orbit data.
Imagine you put at night a transparent sheet on the window and
then you mark very fast all spots on the night sky.
Half an hour later you take another sheet of transparent film and
repeat the whole procedure.
Then you put both sheets on each other in a way that the many spots
of the stars on sheet one align with their counterparts on sheet two.
This is possible because the distance to the stars is so big, that
their movement is not visible in a short period.
But some spots will not align with another spot. These objects have
moved visibly in the last half hour since they are
much closer than the stars. First there are the nine planets of
our solar system. But there are more, much fainter spots. These
are some of the many asteroids in our solar system. There are several efforts to estimate the options on how to deal with an approaching asteroid , like altering its course when it is still far away from earth. In such an event, only a comparable small amount of energy is needed. A nuclear explosion may change the course of an asteroid or break it up in more manageable pieces. Another option is to move a smaller asteroid against a threading asteroid, deflecting it like a billiard ball pushed against another.
For the first time in the history of mankind
we have the technological basics to do something against this kind of danger.
Independently of what one may believe, think or say about the collision probabilities,
it will hardly affect the actual course of these mountains in the sky.
The race against the time begins at the moment when one has the
ability to do something.
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