Planets
Asteroid Belt:
On the border between the stony planets and gas giants we find the asteroid belt, a zone where no single planet but a lot miniplaneetjes through the solar system move.
There are many thousands of these planets (planetoids or asteroids), which all have their own name. To cataloging them easier, they all get a number, in order of their
discovery. The first discovered asteroid Ceres is one example.
View and surface:
Asteroids are very small. 1 Ceres, the largest of all, it is 930 km wide. 2 Pallas and 4 Vesta is about 500 km wide. Most measure only a little kms. but the very
largest asteroids are not around: most are vaguely oval or "potato-shaped".
Meanwhile, there are further away in the solar system discovered a number of objects that are larger than Ceres, and almost as large as Pluto. These are cooper
objects, the icy brothers of the stony, metallic or carbonaceous asteroids.
NEAR discovered that the asteroid Eros is covered with a thick layer of fine regolith, as the moon is the case. Perhaps partly consists of micrometeorites and partly
of debris from the asteroid was loosened by smashing these micrometeorites.
Recently it has been discovered that an asteroid sometimes consists of several pieces of stone that just float together, such as 4769 Castalia. Sometimes it to two or
three large boulders that will revolve around each other, but sometimes an asteroid also consists of a large lot of small stones, as might be the case in 1620
Geographos. The Galileo probe found that the planetoide243 Ida has a small moon, Dactyl that was baptized. That moon is no extra than 1.5 kilometer wide.
The Hubble Space Telescope has discovered large color contrasts on asteroid Vesta, similar to the dark areas on the Moon (lava plains are called "seas"). That means
that on Vesta magma must have flowed from the interior of the asteroid. This cast a totally new light on asteroids, once thought that the blocks of stone were extinct
since the birth of the solar system hardly had changed. For now, however, Vesta is the only asteroid which found traces of geological activity that are related to
impact features.
Vesta was probably hit about 4 billion years ago by a slant that rending away part of its crust, and so brought the dark (liquid) mantle to the surface. So as Vesta
offers us actually look at her inner. Moreover, a number of terrestrial meteorites exhibit many similarities with Vesta, scientists assumed that dare assume that they
are dealing with original pieces of the crust associated with that collision come loose, and after a journey through the solar system on earth crashed. Even those
meteorites (found in 1970) indicate volcanic activity. Finally, an entire family were also smaller asteroids discovered near Vesta, which probably also originally part
of the mantle of the asteroid.
Composition:
In terms of chemical composition, we distinguish three types of asteroids: C, S, and the smaller group M. The C-type state for carbonaceous asteroids while S stands
for asteroids that predominantly contain silicates. Rare M-types are metallic. On the basis of observations of the color of asteroids and measurements of their
reflectivity by the IRAS satellite could which three families are further divided into 14 subtypes, according to their composition.
The C group is the largest and contains about 3/4 of all asteroids. Asteroids of this group are very dark. Some contain compounds that indicate that they used to have
that water has entered into connections with the minerals present. A small portion of the asteroids in the C group, especially those who are on the outside of the
asteroid belt, are dark red. This suggests that their surface contains organic substances.
Approximately 1/6 of the asteroids is quite clear and reddish in color. This is the S-group. They consist of silicates with iron compounds.
The smaller M-group, finally, consists mainly of nickel and iron, without any trace of silicates. They exist so probably entirely of metal, and may be left over (parts
of) iron cores of planetesimals that their older stone mantle are completely lost in a giant collision.
Also cooper objects and Centaurs are classified as asteroids, although they consist mainly of ice and thus more akin to comets. These objects are not discussed here.
Origins and evolution
The origin of the asteroid belt is quite easy to explain: while in the early solar system anywhere planetesimals collided, samenklonterden and shaped planets, could
not do that at the place between Mars and Jupiter. Probably is the great attraction of Jupiter here for something in between.
Jobs and families:
Most asteroids we find located in an elliptical orbit between Jupiter Marches, roughly in the plane of the ecliptic.
Although there are a lot of asteroids, they come very rarely together or a planet around: the space through which they float is very large, and the asteroids
themselves are very small. Yet it must occasionally prevent two asteroids collide. Unless there is a large difference in mass, the two asteroids will usually break
into pieces. Only at the very heavy collisions will all those little pieces in different jobs to reach the sun, and thus new asteroids. In several states, the remnants
together in the area, in what is called "Hirayama families". Such families are usually also characterized by a cloud of dust, resulting from the collision.
A large family of asteroids located on the orbit of Jupiter. These are called Trojans because every asteroid in this family is named after a hero of the Greek story of
the Trojan War. By gravity, these Trojans divided into two families: one group is in orbit before Jupiter, the other group follows the planet.
There are also some asteroids that are in orbit near the Earth. This family is called "Near Earth Objects". 1 of this is the asteroid Eros(god of love), was from
February 2000 until February 2001 that examined the spacecraft near.
The satellites of Mars, Phobos and Deimos, are probably asteroids captured by the Martian gravity. The gas giants have some irregular moons, which are captured asteroids.
Research:
In new years there has been a transformed focus on asteroids: the public interest was aroused by theories that the impact of an asteroid associated with the
disappearance of the dinosaurs, or even an imminent catastrophe predicted that would put an end to our civilization. No matter how small the chances of such a
devastating impact, still keeping an eye on asteroids space agencies who come too close to the earth. Other motives, however, the interest in these small planets been
tightened at the scientific level, they can teach us more about the origins of the solar system. In economic terms, they may be suitable for future mining: they are
rich in minerals.
The increased interest is particularly evident in the number of probes that can be output to asteroids. The most spectacular example so far is the NEAR probe, which in
1997 first asteroid 253 Mathilde Visited and in February 2000 at the nature shearer 433 Eros arrived and from orbit around the asteroid for a year conducted extensive
research. At the end of the NEAR mission was always closer to the asteroid, the probe crashed there in the end, and thus the first "landing" conducted on an asteroid.
The latest photo NEAR sent it was taken from a height of 25 meters above the surface.
0 comments: