Planetary system

Of particular interest to astrobiology is the habitable zone of planetary systems where planets could have surface liquid water, and thus, the capacity to support Earth-like life.

[6] The idea was first proposed in Western philosophy and Greek astronomy as early as the 3rd century BC by Aristarchus of Samos,[7] but received no support from most other ancient astronomers.

De revolutionibus orbium coelestium by Nicolaus Copernicus, published in 1543, presented the first mathematically predictive heliocentric model of a planetary system.

17th-century successors Galileo Galilei, Johannes Kepler, and Sir Isaac Newton developed an understanding of physics which led to the gradual acceptance of the idea that the Earth moves around the Sun and that the planets are governed by the same physical laws that governed Earth.

In the 16th century the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets.

[8] In the 18th century, the same possibility was mentioned by Sir Isaac Newton in the "General Scholium" that concludes his Principia.

Planets found around pulsars may have formed as a result of pre-existing stellar companions that were almost entirely evaporated by the supernova blast, leaving behind planet-sized bodies.

[10] Fallback disks of matter that failed to escape orbit during a supernova may also form planets around black holes.

If an evolved star is in a binary or multiple system, then the mass it loses can transfer to another star, forming new protoplanetary disks and second- and third-generation planets which may differ in composition from the original planets, which may also be affected by the mass transfer.

Studies suggest that architectures of planetary systems are dependent on the conditions of their initial formation.

Theories, such as planetary migration or scattering, have been proposed for the formation of large planets close to their parent stars.

In addition, statistical analyses indicate that lower-mass stars (red dwarfs, of spectral category M) are less likely to have planets massive enough to be detected by the radial-velocity method.

After planets, circumstellar disks are one of the most commonly-observed properties of planetary systems, particularly of young stars.

The Solar System possesses at least four major circumstellar disks (the asteroid belt, Kuiper belt, scattered disc, and Oort cloud) and clearly-observable disks have been detected around nearby solar analogs including Epsilon Eridani and Tau Ceti.

Based on observations of numerous similar disks, they are assumed to be quite common attributes of stars on the main sequence.

Computer modelling of an impact in 2013 detected around the star NGC 2547-ID8 by the Spitzer Space Telescope, and confirmed by ground observations, suggests the involvement of large asteroids or protoplanets similar to the events believed to have led to the formation of terrestrial planets like the Earth.

[43][44] Planetary systems can be categorized according to their orbital dynamics as resonant, non-resonant-interacting, hierarchical, or some combination of these.

Single and multiple planets could be captured into arbitrary unaligned orbits, non-coplanar with each other or with the stellar host spin, or pre-existing planetary system.

Planets would be unlikely to be captured around neutron stars because these are likely to be ejected from the cluster by a pulsar kick when they form.

After the cluster has dispersed some of the captured planets with orbits larger than 106 AU would be slowly disrupted by the galactic tide and likely become free-floating again through encounters with other field stars or giant molecular clouds.

Habitable zones have usually been defined in terms of surface temperature; however, over half of Earth's biomass is from subsurface microbes,[50] and temperature increases as depth underground increases, so the subsurface can be conducive for life when the surface is frozen; if this is considered, the habitable zone extends much further from the star.

[d] Several candidates have been identified, but spectroscopic follow-up studies of their atmospheres are required to determine whether they are like Venus.

Population I stars have regular elliptical orbits around the Galactic Center, with a low relative velocity.