Our Solar System

Formation and Composition of the Solar System

• The Solar System was formed approximately 4.6 billion years ago from a dense region of a molecular cloud.
• The Sun is a typical G-type main-sequence star that maintains equilibrium through the fusion of hydrogen into helium at its core.

Planets in the Solar System

• The eight planets that orbit the Sun, in order, are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
• The four terrestrial planets have solid surfaces.
• The two gas giants (Jupiter and Saturn) and two ice giants (Uranus and Neptune) do not have a definite surface, comprising mainly gases and liquids.

Mass Distribution in the Solar System

• Over 99.86% of the Solar System's mass is in the Sun.
• Nearly 90% of the remaining mass is in Jupiter and Saturn.

Dwarf Planets

• There is a strong consensus that the Solar System has at least nine dwarf planets: Ceres, Orcus, Pluto, Haumea, Quaoar, Makemake, Gonggong, Eris, and Sedna.

Small Solar System Bodies

• The Solar System contains a vast number of small bodies, including asteroids, comets, centaurs, meteoroids, and interplanetary dust clouds.
• Some of these bodies are located in the asteroid belt (between Mars's and Jupiter's orbit) and the Kuiper belt (just outside Neptune's orbit).

Natural Satellites

• Six planets, seven dwarf planets, and other bodies have orbiting natural satellites, commonly called 'moons'.

Heliosphere and Heliopause

• The Solar System is constantly flooded by the Sun's charged particles, the solar wind, forming the heliosphere.
• The solar wind is halted around 75–90 astronomical units from the Sun, resulting in the heliopause, which marks the boundary of the Solar System to interstellar space.

Oort Cloud and Proxima Centauri

• The outermost region of the Solar System is the theorized Oort cloud, the source for long-period comets, extending to a radius of 2,000–200,000 AU.
• The closest star to the Solar System, Proxima Centauri, is 4.25 light-years (269,000 AU) away.

Learn about the formation and structure of our solar system, including the Sun and its orbiting objects. Discover how the Sun maintains its equilibrium and more!