Planetary Systems Category

A planetary system is a set of gravitationally bound non-stellar objects in orbit around a star or star system. Generally speaking, planetary systems describe systems with one or more planets, although such systems may also consist of bodies such as dwarf planets, asteroids, natural satellites, meteoroids, comets and planetesimals as well as discernable features including circumstellar disks. The Sun together with its planetary system, which includes Earth, is known as the Solar System. The interchangeable terms extrasolar system and exoplanetary system are sometimes used in reference to other planetary systems. Individually they may be referred to as system prefixed by the name of the star or star system that it orbits or sometimes simply the name of the star system.

For a long time after the 16th century and Copernican heliocentrism, human knowledge of planetary systems was limited to heliocentrism and the Solar System. Despite the discovery and exploration of the Solar System and centuries of conjecture, it remained this way until the groundbreaking discovery of the unusual PSR B1257+12 system and its extrasolar planets, confirmed in 1992, which holds a number of significant records, including the first discovered, as well as the first pulsar, multi-star planetary system.

The 21st century has become a golden era of planetary system discovery, with findings occurring at a rapid rate. A total of 1792 such planets (in 1112 planetary systems, including 460 multiple planetary systems) have been identified as of 20 May 2014. Hundreds more systems are unconfirmed. In terms of total confirmed planets, the Solar System with 8 remains the largest known planetary system. However, HD 10180 may have as many as 9 planets, of which 2 are unconfirmed, and is the largest known exoplanetary system along with Kepler-90, which also has 7 confirmed planets. A wide range of planetary systems have been discovered, with a variety of different orbital arrangements around different types of stars. The closest confirmed system is Gliese 832 at 14.8 light years (ly) with one confirmed planet, whereas the closest unconfirmed system is Alpha Centauri at 4.37 ly with a planet of Earth mass. The closest multi-planet system is Gliese 876 at 15.3 ly with four confirmed planets.

Although knowledge of the nature of planetary systems, including that of the Solar System, has increased considerably, much is unknown about their origin and evolution and current theories of their formation and evolution are relatively new to the field of planetary science.

Of particular interest to astrobiology is the habitable zone of planetary systems, believed to be the region with the most potential to develop and sustain extraterrestrial life.

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