Planetary system

planetary systemssolar systemssystemextrasolarsolar systemstar systemplanetplanet formationplanet systemstar systems
A planetary system is a set of gravitationally bound non-stellar objects in or out of orbit around a star or star system.wikipedia
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Star system

multiple star systemtriple starmultiple systems
A planetary system is a set of gravitationally bound non-stellar objects in or out of orbit around a star or star system.
Star systems are not to be confused with planetary systems, which include planets and similar bodies [such as comets.]


planetsFormer classification of planetsplanemo
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.
As of, known extrasolar planets in planetary systems (including multiple planetary systems), ranging in size from just above the size of the Moon to gas giants about twice as large as Jupiter have been discovered, out of which more than 100 planets are the same size as Earth, nine of which are at the same relative distance from their star as Earth from the Sun, i.e. in the circumstellar habitable zone.


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.
This interdisciplinary field encompasses research on the origin of planetary systems, origins of organic compounds in space, rock-water-carbon interactions, abiogenesis on Earth, planetary habitability, research on biosignatures for life detection, and studies on the potential for life to adapt to challenges on Earth and in outer space.


orbitsorbital motionplanetary motion
A planetary system is a set of gravitationally bound non-stellar objects in or out of orbit around a star or star system.
Within a planetary system, planets, dwarf planets, asteroids and other minor planets, comets, and space debris orbit the system's barycenter in elliptical orbits.

Stars and planetary systems in fiction

47 Ursae Majoris in fictionArcturus61 Cygni
Long before their confirmation by astronomers, conjecture on the nature of planetary systems had been a focus of the search for extraterrestrial intelligence and has been a prevalent theme in fiction, particularly science fiction.
The planetary systems of stars other than the Sun and the Solar System are a staple element in many works of the science fiction genre.

PSR B1257+12

PSR 1257+12PSR B1257+12 DLich (pulsar)
The first confirmed detection of an exoplanet was in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12.
The pulsar has a planetary system with three known planets, named "Draugr" (PSR B1257+12 b or PSR B1257+12 A), "Poltergeist" (PSR B1257+12 c, or PSR B1257+12 B) and "Phobetor" (PSR B1257+12 d, or PSR B1257+12 C), respectively.

Rogue planet

free-floating planetsfree-floating planetfree-floating planetary-mass object
During formation of a system much material is gravitationally scattered into far-flung orbits and some planets are ejected completely from the system becoming rogue planets.
Such objects have been ejected from the planetary system in which they formed or have never been gravitationally bound to any star or brown dwarf.

Solar System

outer Solar Systeminner Solar Systemouter planets
The Sun together with the planets revolving around it, including Earth, is known as the Solar System.
This high metallicity is thought to have been crucial to the Sun's development of a planetary system because the planets form from the accretion of "metals".

Nebular hypothesis

planet formationplanetary formationformation
Observations using the Spitzer Space Telescope indicate that extremely massive stars of spectral category O, which are much hotter than the Sun, produce a photo-evaporation effect that inhibits planetary formation.
It is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System (as well as other planetary systems).

Interplanetary dust cloud

interplanetary dustzodiacal clouddust
Interplanetary dust clouds have been studied in the Solar System and analogs are believed to be present in other planetary systems.
The interplanetary dust cloud, or zodiacal cloud, consists of cosmic dust (small particles floating in outer space) that pervades the space between planets within planetary systems such as the Solar System.

Accretion disk

accretion discaccretion disksaccretion
Alternatively, planets may form in an accretion disk of fallback matter surrounding a pulsar.
Accretion disks surrounding T Tauri stars or Herbig stars are called protoplanetary disks because they are thought to be the progenitors of planetary systems.

Kepler space telescope

KeplerKepler MissionKepler Space Observatory
The frequency of detections has increased since then, particularly through advancements in methods of detecting extrasolar planets and dedicated planet finding programs such as the Kepler mission.
The scientific objective of the Kepler space telescope was to explore the structure and diversity of planetary systems.

51 Pegasi

51 Peg51 Peg (Helvetios)a star
The first confirmed detection of exoplanets of a main-sequence star was made in 1995, when a giant planet, 51 Pegasi b, was found in a four-day orbit around the nearby G-type star 51 Pegasi.
At the time of its discovery, this close distance was not compatible with theories of planet formation and resulted in discussions of planetary migration.


Extrasolar moonmoonmoons
Based on observations of the Solar System's large collection of natural satellites, they are believed common components of planetary systems; however, exomoons have so far eluded confirmation.
It is inferred from the empirical study of natural satellites in the Solar System that they are likely to be common elements of planetary systems.

Red giant

red giant starred giantsred giant stars
As stars evolve and turn into red giants, asymptotic giant branch stars, and planetary nebulae they engulf the inner planets, evaporating or partially evaporating them depending on how massive they are.
Although traditionally it has been suggested the evolution of a star into a red giant will render its planetary system, if present, uninhabitable, some research suggests that, during the evolution of a star along the red-giant branch, it could harbor a habitable zone for several billion years at 2 astronomical units (AU) out to around 100 million years at 9 AU out, giving perhaps enough time for life to develop on a suitable world.

Upsilon Andromedae

υ Andromedaeυ AndUpsilon Andromedae A
The only system where mutual inclinations have actually been measured is the Upsilon Andromedae system: the planets, c and d, have a mutual inclination of about 30 degrees.
This was both the first multiple-planet system to be discovered around a main-sequence star, and the first multiple-planet system known in a multiple star system.

Protoplanetary disk

protoplanetary discprotoplanetary disksprotoplanetary discs
Planetary systems come from protoplanetary disks that form around stars as part of the process of star formation.


The Kepler-223 system contains four planets in an 8:6:4:3 orbital resonance.
Kepler-223 (KOI-730, KIC #10227020) is a G5V star with an extrasolar planetary system discovered by the Kepler mission.


They also contain a small proportion of heavier elements, and this fraction is referred to as a star's metallicity (even if the elements are not metals in the traditional sense), denoted [m/H] and expressed on a logarithmic scale where zero is the Sun's metallicity.
The more metals in a star and thus its planetary system and proplyd, the more likely the system may have gas giant planets and rocky planets.

List of exoplanetary host stars

List of stars with confirmed planetshost starcaptured
The two most important stellar properties are mass and metallicity because they determine how these planetary systems form.

List of multiplanetary systems

List of planetary systemsList of stars with extrasolar planetsmultiple planetary systems
The two most important stellar properties are mass and metallicity because they determine how these planetary systems form.

OTS 44

At the low-mass end of star-formation are sub-stellar objects that don't fuse hydrogen: the brown dwarfs and sub-brown dwarfs, of spectral classification L, T and Y. Planets and protoplanetary disks have been discovered around brown dwarfs, and disks have been found around sub-brown dwarfs (e.g. OTS 44).
It could eventually develop into a planetary system.

Beta Pictoris

β Picβ Pictoristhat more famous system
The first exocomets were detected in 1987 around Beta Pictoris, a very young A-type main-sequence star.
In 2011 the disk around Beta Pictoris became the first other planetary system to be photographed by an amateur astronomer.


Morning Starevening starplanet Venus
Many compact systems with multiple close-in planets interior to the equivalent orbit of Venus are expected to have very low mutual inclinations, so the system (at least the close-in part) would be even flatter than the solar system.

Galactic tide

tidal forcestidal interactiontidal tails
After the cluster has dispersed some of the captured planets with orbits larger than 10 6 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.
This can have consequences for the formation of stars and planetary systems.