Planetary system

Our solar system or planetary system as it is also known, is filled with a great variety of celestial bodies that include the sun, planets, dwarf planets and asteroids, and on Earth , life itself. Comets occasionally arrive in the inner solar system, entering from the outer reaches of the solar system in highly elliptical orbits . A planetary system is a set of non-stellar objects gravitationally bound in an orbit around a star or stellar system. . In other words, planetary systems describe systems that have one or more planets, although such systems can also consist of bodies such as dwarf planets , asteroids , natural satellites , meteorites , comets, and planetesimals , as well as discernible features, including circumstellar disks.

What is planetary system?

The planetary system is what we more commonly know as the solar system , in which we find bodies that are part of a binary star system and that are found revolving around the sun , the earth and the planets.

Characteristics of a planetary system

The main characteristics of the planetary system are the following:

  • In the case of the solar system, it is formed by a central star which we know by the name of the Sun and by the bodies that accompany it.
  • It is formed by a central star or several that are known as stellar system , and different objects orbiting around it.
  • The eight planets of the solar system gravitate around the Sun and they do so in elliptical orbits .
  • The planets of the solar system are positioned in orderly orbits at increasing distances from the sun.

Types of planetary systems

Astronomers classify it by type. Certain types of stars are known to produce specific types of planetary systems , and are classified by the spectral type of the host star. Main sequence stars like the Sun represent most of the discoveries of the planetary system. They are generally classified by size and types of planets and their orbital configuration.

Hot Jupiter systems with a gas giant very close to the star is one of the most common found so far and Hot Neptune- type systems have also been found .

Theories, such as scattering , have been proposed for the formation of large planets near their parent stars . Dusty discs with a wide ring of dust and comets are another common type of system.

The protoplanetary disks, still in formation, have also been discovered. Currently, few systems with their own analogues have been found with terrestrial planets close to the parent star.

Formation of a planetary system

The formation of a planetary system occurs in phases:

  • In the first phase , which is known as the collapse of the interstellar cloud , it is explained that the systems originate from huge molecular clouds made up of hydrogen , helium and lithium in addition to various heavy elements. From each of these clouds a star will be born and probably a system of planets .
  • The second phase is the formation of planetesimals that are aggregates of material that give rise to objects with more mass. These particles are grouped in formations that measure several kilometers and the result is a swarm of them.
  • The third stage is called planetary embryo formation and they take 1 to 10 million years to form. The collisions cause them to break apart and gravity makes their orbits very messy.
  • The fourth stage is the formation of the first giant planet that is called the planetary embryo and grows at a rapid rate. The growth process produces a lot of heat so the planet can shine like its star . As it grows, the last phases occur that include the formation of other giant planets , the formation of rocky planets and the elimination of excess gas.


Throughout history there have been different models of planetary systems, among which we can mention the most important:

  • Aristotelian Model : considered the most important and said that the earth occupied the center of the universe . The terrestrial bodies are formed by the combination of four elements: earth, water, air and fire . He claimed that the celestial region had concentric spheres surrounding the earth and that in each sphere there were celestial bodies.
  • Geocentric model : Ptolemy proposed a model with the Earth in the center, stationary, and the planets , the Moon and the Sun had orbits around it. Ptolemy proposed a geometric theory to mathematically explain the movements and positions of the planets, the Sun and the Moon.
  • Heliocentric model: where the sun was the center of the universe , and that the earth and the planets had circular paths around them. The stars were fixed and far from the sun and the earth rotated on its own axis.


Some examples of planetary systems are as follows:

  • Alpha Centauri :  is thethat is more near the Earth. There is still no confirmation of the existence of the worlds around their stars . It is located 4.3 light years from the solar system and has two stars around which a planet could orbit.
  • Epsilon Eridani:  this planetary system has already been confirmed and is the one that is closest to Earth. Located about 10.5 light years away, it has a star slightly smaller than the Sun, a planet that is larger than Earth and that forms in its disk of dust and an asteroid belt .
  • Epsilon Indi: it  is composed of three stars , one of them is larger, approximately two thirds of the mass of the Sun and the other two smaller stars, and are known as brown dwarf stars .
  • Tau Ceti:  in it is a star similar to the Sun , and 5 planets orbiting. According to scientists, this planetary system could be an option to host life since two of the exoplanets could be in the habitable zone.

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