Extrasolar 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 2,682 known planetary systems, including 602 systems consisting of multiple planets as of 1 February 2017. These systems contain more than 3,572 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, and thus the capacity to harbor Earth-like life.

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).

The notion of a heliocentric Solar System, with the Sun at the center, is possibly first suggested in the Vedic literature of ancient India, which often refer to the Sun as the "centre of spheres". Some interpret Aryabhatta's writings in Āryabhaṭīya as implicitly heliocentric.

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