Search for Planets

Formation of the Solar System

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Terrestrial planets in our Solar System (Mercury, Venus, Earth and Mars) have a relatively small size and are primarily made of rock and metals. They are thought to form by core accretion, which involves dust particles in the disk sticking together to form increasingly larger bodies or planetesimals, that eventually form planets by collisional growth.

Giant planets (Jupiter, Saturn, Uranus, Neptune) orbit further from the Sun and consist of a solid core surrounded by a gaseous envelope. Planetesimal accretion can also explain the formation of these cores, which subsequently capture gas from the surrounding disk.

The new extrasolar planets discovered have minimum masses ranging from about 0.1 to 10 Jupiter masses. They orbit very close to their parent star and generally have large eccentricities. Planetary formation theories predicted instead nearly circular orbits and giant planets formed far from the star, just as for our own Solar System.

A mechanism called orbital migration has been introduced to account for the displacement of giant planets from their formation site far from the star to small orbital radii. The large eccentricities of new candidate planets are still not clearly understood by present theories.

Solar System Bodies

Between the orbits of Mars and Jupiter lies the asteroid belt. At present about 60 000 asteroids or minor planets have been detected, but how many are there? One million of them - or maybe even more?

Detection and classification of asteroids is of tremendous interest for studies of the formation and evolution of our Solar System, as their composition is thought to have remained unchanged since the birth of our planetary system. In the outer limits of the Solar System, have other Pluto-like bodies escaped detection so far?

Click on the thumbnail below to see a narrated movie explaining the formation of the planets:

Formation of the Planets

Click on the thumbnail below to see a computer animated model of the asteroid belt:

Asteroid belt


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