Additional Data:

Average distance to the sun:	299.000.000 to 508.000.000 km
Diameter of an asteroid:	50 m to 250 km
Weight of all asteroids together:	0,000615 earth masses
Number of asteroids:	800.000 discovered so far
Number of dwarf planets	1

 

Towards the end of the 18th century, numerous astronomers were on the hunt for a suspected "missing" planet in the "gap" between Mars and Jupiter. Despite the great attention paid to this region, the first asteroid was not discovered until 1801 by the Italian astronomer Giuseppe Piazzi. This discovery was the result of a coincidence. The celestial body, christened "Ceres", was initially thought to be the missing planet, but in 1802 and 1807 three similar celestial bodies, Pallas, Juno and Vesta, were discovered in the same region. The celestial bodies thus sighted were grouped into the class of asteroids, which means "similar to stars" in Greek. Instead of asteroids, we now speak of small bodies that are defined in such a way that they are not alone in their orbit and that they are not heavy enough to form into a sphere. They form a belt between Mars and Jupiter, within which about 800,000 objects have been found so far. Of these, only about 14,000 were given a name, the rest were catalogued with a sequential number. Contrary to popular depictions, the asteroid belt can be safely crossed with a space probe. Despite their large numbers, the individual asteroids are on average as far apart as the Earth and the Moon.

Asteroids are now considered to be remnants of the time when the planets formed around the sun. In the process, more and more dust and gas clumped together until a solid lump was formed, which was able to attract and absorb more and more material with the help of its gravity. However, Jupiter's very strong gravity in particular ensured that the existing material in today's asteroid belt could not form into another celestial body. Instead, the objects collided there again and again, causing more and more fragments on their own orbits.

Asteroids can be divided into three families: C asteroids, S asteroids and M asteroids. Most asteroids are predominantly carbon and belong to the C asteroids. They have a dark coloration with a reddish tinge and resemble the carbonaceous chondrites, a group of stony meteorites. Around 17% of asteroids are S-asteroids, which contain a lot of silicon. These asteroids have probably undergone a heating and melting process and usually have a brighter surface. A few asteroids are metallic and are called M-asteroids. They consist mainly of iron-nickel compounds. It is likely that these asteroids are cores of earlier larger bodies whose outer layers of rock were blasted away in collisions.

Since asteroids are very light compared to planets, they can be deflected out of their orbit by their gravity under certain circumstances. If this happens, then the probability increases that they can collide with another celestial body on their new orbit. In the course of Earth's history, there have been repeated devastating impacts on Earth. The last major impact took place 65 million years ago, when an asteroid more than 10 km in diameter wiped out the dinosaurs. Astronomers are therefore measuring the orbits of all known asteroids to see if they could pose a threat. Several probes have already visited asteroids and also returned samples to Earth.

Even today, asteroids can still be named after the suggestion of their discoverer. But certain rules and standards are in place: new names must not be offensive and must not have any echoes of political or military leaders.

Ceres also orbits in the asteroid belt. It was discovered as an asteroid, but due to its diameter of 950 km and spherical shape, it is now classified as a dwarf planet similar to Pluto.

Since asteroids have only a small gravity of their own, it is very easy to land on them and launch from them again. Water in the form of ice is suitable for the production of oxygen and rocket fuel. Metals such as iron and aluminum can be turned into rocket parts out of finely ground powder using a 3D printer. Precious metals such as copper, silver, gold and platinum can be used for circuits and rare earths for solar cells, batteries and sensors. All these raw materials do not have to be lifted out of the Earth's gravitational field and would therefore be much cheaper to get in space.