What are asteroids and comets

Asteroids and comets - millions of objects


Our solar system consists not only of planets and moons, but also of numerous other objects, the frequency of which is in the millions. These are asteroids and comets.

Vagabonds in the solar system

About 4.5 billion years ago, gas and dust began to concentrate around the sun and eventually clump together. Initially, countless small solids were created, some of which grew larger and larger over time, until they reached dimensions of a few kilometers. At that time it must have been quite uncomfortable around the sun, because these so-called planetesimals - building blocks for the later planets - were constantly in each other's path on their trajectories around the sun and often collided with each other. In this way, on the one hand, the planets and moons were created and, on the other hand, countless smaller objects were left over as “rubble”. Especially in the first billion years of our solar system, the planets and moons that have now existed were often hit by such debris. The craters formed in the process can still be seen on some celestial bodies today.
In the meantime, impacts with great damage on earth have become very rare. But that doesn't mean they can't take place. For example, an asteroid struck the earth 65 million years ago, which resulted in the destruction of most of earthly life, including the extinction of the dinosaurs.

Due to their age and the largely unchanged matter, asteroids and comets are ideal research objects to find out important information about the early days of the formation of planets.


The asteroids, also known as asteroids or minor planets, occur in the entire planetary system, but accumulate in the main asteroid belt between Mars and Jupiter (over 90 percent). Another important collection of asteroids - the Kuiper Belt - is in an orbit beyond Neptune. But some bodies also move within the orbit of Mars.

The first asteroids were discovered between 1801 and 1807. The beginning was made in 1801 by Ceres, which was soon followed by Pallas, Juno and Vesta. It was almost 40 years before the fifth asteroid, Astraea (1845), was discovered. Only now is it possible to record even the smallest boulders with sophisticated observation technology. This means that the number of objects found continues to increase. So far 540,723 asteroids have been found in the solar system (as of November 28, 2010).


Comets, often referred to as "dirty snowballs" due to their composition of ice, dust and organic components, are probably the oldest, largely unchanged remains of the gigantic disk of dust from which our solar system arose around 4.4 billion years ago. While the raw material from which the planets and moons were once formed has been constantly changing over billions of years due to geological, chemical and biological processes, it has remained in its original state in the comets.

The greatest number of them orbits the sun in an area far outside the orbits of the planets, in the Oort cloud. However, due to gravitational disturbances from other stars, some get into orbits that pass close to the sun. Parts of their ice core then begin to evaporate and thus form the characteristic cometary tails. Comets are usually a few kilometers in size. There are hardly any smaller objects because they evaporate relatively quickly when they are close to the sun.

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