The Solar System was formed approximately 4.6 billion years ago and consists of the Sun, planets, dwarf planets and other astronomical objects bound in its orbit. The formation was cause by the collapse of a giant molecular cloud, the mass at the centre collecting to form the Sun and a flat disk of dust around it which the planets and other bodies would eventually be formed from.

  • The two outermost gas giants, Uranus and Neptune, are composed largely of ices, (water, ammonia and methane) and are sometimes also referred to as the “ice giants“.
  • The two innermost gas giants, Jupiter and Saturn, are the larger of the four and are composed mainly of hydrogen and helium.
  • The four outer planets, also known as the “gas giants” (Jupiter, Saturn, Uranus and Neptune), are substantially larger and more massive than the inner planets.
  • The four smaller inner planets, also known as the “terrestrial planets” (Mercury, Venus, Earth and Mars), are primarily composed of rock and metal.
  • Other objects of note in the Solar System are the dwarf planets (Ceres, Pluto, Haumea, Makemake & Eris), moons, asteroids, the asteroid belt, comets and the Kuiper belt.
  • 99.86% of the system’s mass is found in the Sun and the majority of the remaining 0.14% is contained within the solar system’s eight planets.
  • As of 2008, there are also five dwarf planets: Pluto, Ceres, Eris, Makemake & Haumea.
  • Astronomers such as Nicolaus Copernicus, Galileo Galilei, Johannes Kepler and Isaac Newton helped develop a new model that explained the movement of the planets with the Sun at the center of the Solar System.
  • For thousands of years humans were unaware of the Solar System and believed that Earth was at the center of the Universe.
  • The inner planets (also known as terrestrial planets) are smaller and made mostly of rock and metal.
  • The outer planets (also known as gas giants) are much larger and made mostly of hydrogen, helium and other gases.
  • The Solar System formed around 4.6 billion years ago.
  • The solar system includes the Sun and all the objects that orbit around it due to its gravity. This includes things such as planets, comets, asteroids, meteoroids and moons.
  • The Sun contains 99.86 percent of the Solar System’s known mass, with Jupiter and Saturn making up making up most of the rest. The small inner planets which include Mercury, Venus, Earth and Mars make up a very small percentage of the Solar System’s mass.
  • There are eight planets in the Solar System. The four inner planets are Mercury, Venus, Earth and Mars while the four outer planets are Jupiter, Saturn, Uranus and Neptune.
  • There is an asteroid belt which lies between the orbits or Mars and Jupiter, it features a large number of irregular shaped asteroids.
  • There are 5 officially recognized dwarf planets in our solar system, they are Ceres, Pluto, Haumea Makemake and Eris. With the exception of Ceres, which is located in the asteroid belt, the other dwarf planets are found in the outer solar system. There are another 6 objects in our solar system that are almost certainly dwarf planets and there may as many as 10,000. Of the dwarf planets only 2 have been visited by space probes, in 2015 NASA’s Dawn and New Horizons missions reached Ceres and Pluto respectively.
  • Dwarf planets share many of the same characteristics as planets though there is one significant difference. The International Astronomical Union’s definition of a dwarf planet is:
  • What Is Dwarf Planet?
  • A “dwarf planet” is a celestial body that
    (a) is in orbit around the Sun,
    (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape,
    (c) has not cleared the neighborhood around its orbit, and
    (d) is not a satellite.
  • The key difference is that a planet has cleared other objects in the area of its orbit while a dwarf planet has not.