Planetary system

A planetary system is a set of gravitationally bound non-stellar objects in orbit around a star or star system. Generally speaking, systems with one or more planets constitute a planetary system, although such systems may also consist of bodies such as dwarf planets, asteroids, natural satellites, meteoroids, comets, planetesimals and circumstellar disks. The Sun together with its planetary system, which includes Earth, is known as the Solar System. The term exoplanetary system is sometimes used in reference to other planetary systems.

There are at least 1321 known planetary systems, including 507 systems consisting of multiple planets as of 10 February 2016. These systems contain more than 2073 known exoplanets. Debris disks are also known to be common, though other objects are more difficult to observe.

Of particular interest to astrobiology is the habitable zone of planetary systems where planets could have surface liquid water.

History

Heliocentrism

Historically, heliocentrism (the doctrine that the Sun is the centre of the universe) was opposed to geocentrism (placing the Earth at the center of the universe).