Extrsolar planets which are also called exoplanets are planets orbiting starts other than the sun.Astronomers have afound more than 160 such planets.Finding and studingextrasolar planets helps astronomers learn more about the formation of our solar system. It also constributes to the study of possible life in the univerese,because life is more likely to develop on planets then in the extremes of stars and empty space. Astronomers did not develop reliable techniques to find extrasolar planets untils the 1990s, but more than 10 new solar systems were dicovered within the first few years of searching. Many astronomers believe that almost every sun like star has a solar system at some point in its development. Astronomers have found that most young stars are sourrounded by disks composed of dust and gas. Some of these disk around the star Formalhaut, show an empty space in the disk. Astronomers believe that dust in this area could be in the process of condensig into a planet. By studying our solar system,astronomers developed a theory of how solar systems form known as the core accretion theory.However,many of the extrasolar planets and disks of dust around other stars do not seem to conform to this theory.The theory states that a disk of dust and gas collects around a star as the star forms.Bits of dust in the disk collide and stick together,forming larger and larger chunks of rock and ice.
Farther out from the star the gases in the disk freeze,adding to the mass available to form these chunks. The pieces of rock continue to collie,forming large objects called protoplanets. The protoplanets far from the star are far larger than those closer to the star because of the increased amount of frozen gas material available.Sometimes protoplanets crash together, breaking apart and starting the process of formation all over again.At some point during the last part of the planet formation process,the star goes through a stage in its own evolution in which it blasts away the free gas that remains in the inner solar system. If the protoplanets in the outer solar system are large enough,their gravitational pull grabs this gas and pulls it in toward the protoplanet.These outer protoplanets than become gas-giant planets,with deep layers of dense gas covering their cores.the smaller inner planets lose any gas that surrounds them.Small planets,such as Earth,that have atmospheres develop them later, when volcanic activity releases gases from within the planet.The star settes into a long quiet period,and the protoplanets grow into planets and develop regular orbits.
Farther out from the star the gases in the disk freeze,adding to the mass available to form these chunks. The pieces of rock continue to collie,forming large objects called protoplanets. The protoplanets far from the star are far larger than those closer to the star because of the increased amount of frozen gas material available.Sometimes protoplanets crash together, breaking apart and starting the process of formation all over again.At some point during the last part of the planet formation process,the star goes through a stage in its own evolution in which it blasts away the free gas that remains in the inner solar system. If the protoplanets in the outer solar system are large enough,their gravitational pull grabs this gas and pulls it in toward the protoplanet.These outer protoplanets than become gas-giant planets,with deep layers of dense gas covering their cores.the smaller inner planets lose any gas that surrounds them.Small planets,such as Earth,that have atmospheres develop them later, when volcanic activity releases gases from within the planet.The star settes into a long quiet period,and the protoplanets grow into planets and develop regular orbits.
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