The solar system formed from dust grains and eventually built up into planets. On the way to making planets some dust grains only formed up to a small size (compared to a planet) and remain at this size today. These rocks are called asteroids.
If it wasn’t for these rocks the planets would not have formed as they would have had nothing to form out of but unfortunately these rocks just didn’t disappear and were leftover from the formation process. Most of these asteroids are between Jupiter and Mars and are in the asteroid belt. It is thought that Jupiter formed these bodies by causing collisions with its massive gravity. Because of these collisions bodies kept breaking up into smaller rocks and these would collide with others and prevent the formation of one single large object. Jupiter has a lot to answer for when it comes to asteroid formation!
Unfortunately these asteroids don’t stay in the orbit between Mars and Jupiter but can cause us some hassle. Collisions between asteroids in the asteroid belt and the complex interactions of gravity of the planets and asteroids can cause an asteroid to come out of the asteroid belt and fly in a different trajectory. When these asteroids get closer to Earth they are called near Earth objects (NEO) which also includes comets and any other pieces of space junk that can be a danger to Earth.a
These rogue asteroids mostly tend to avoid hitting the planets causing impact craters and, mass extinctions, poor old dinosaurs. There are many more smaller asteroids than larger ones, the largest being Ceres with a diameter of 913 km, pretty big!
Ceres was called a dwarf planet that was lowered in status to an asteroid some time ago. It is in the asteroid belt and contains almost a third of the belts total mass. Recently it has been seen to be spherical unlike the other asteroids around it which are an irregular in shape. If you were to land on a Ceres you would probably find a mixture of water ice and various hydrated minerals such as clay. It is also thought to have a Rocky core and icy mantle beneath this mantle could be water and all the hope for life that that gives.
No space probes have been to Ceres but there is a mission that is on the way at the moment. This is the dawn mission which should reach Ceres in 2015 after passing by the asteroid 4 Vesta in 2011. It will enter orbit around Ceres at about 6000 km and then reduce its orbital distance to about 700 km taking about 12 months to do this. This is called the Dawn Mission and it will be quite an interesting time when it starts to send back information.
Asteroid can be classified into various types so that scientists who enjoy looking at rocks can chat about them.
C-type- carbonaceous types, dark (reflective), primitive
S-type- Stony or Stony metallic, more reflective, more red, fragments
E-type- highly reflective, enstatite (magnesium silicate MgSiO3), fragments
D-type- (dark type) dark, red, primitive
M-type- (metallic type), mostly iron and nickel, fragments
P-type- (pseudo M type), metallic component
These are only a few types of the classified asteroids and are not the only way to classify them either. A primitive asteroid is one where collisions have not changed the composition or surface features much. These are quite useful asteroids and some have been found on Earth giving us indications of what was around at the time of the formation of the solar system.
Astronomers have noticed, while spending sleepless nights looking through their telescopes, that different classes of asteroid occupy different parts of the asteroid belt. This is because of the distance from the Sun. Obviously if you get closer to the Sun it is hotter and further away it is cooler and this means that elements that melt at lower temperature are not found further away from the Sun but only the elements that can survive the heat of the sun are found.
Asteroids aren’t just balls of rock that are perfectly spherical. Some asteroids are called binary asteroids and orbit each other they are much more common than previously thought. It is quite easy to see the larger asteroids but what about the smaller asteroids? There are a few techniques that are used to work out what shape an asteroid is and are used independently or together. Obviously a spacecraft flyby is first on the list but to have a probe passing by every single asteroid would be just a little bit uneconomical. Radio transmitters used together with telescope dishes like the one in Arecibo give some very detailed information and then there is radar techniques as well that can be used to image the asteroid.
It has been found that most asteroids are rubble fragments bound together by their own gravity. This means that between the rubble fragments there are cavities. C-type asteroids for instance may be 80% porous.
There has actually been a landing an asteroid. The Eros asteroid was approached by the NEAR spacecraft. Eros was the first near Earth asteroid that was discovered. The NEAR spacecraft was sent to intercept Eros and orbited it which was a fine feat in itself but at the end of the mission it was decided to try and make a landing on the asteroid. This was carried out and some great pictures were returned.
Asteroids can be larger pieces of rock that are totally boring but on the other hand they can be very interesting libraries of information of the early solar system. One day of course we will be mining the asteroids for minerals, rock and perhaps water as well for use as a propellant. They can also be used for living on as most of them are porous and have caves and their services will protect the inhabitants from radiation.
For now though we are looking and you can look to as the pictures and information from the asteroids and solar system flood in. Go take a look!