Solar system

The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is a typical star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core, releasing this energy from its outer photosphere. Astronomers classify it as a G-type main-sequence star.

The largest objects that orbit the Sun are the eight planets. In order from the Sun, they are four terrestrial planets (Mercury, Venus, Earth and Mars); two gas giants (Jupiter and Saturn); and two ice giants (Uranus and Neptune). All terrestrial planets have solid surfaces. Inversely, all giant planets do not have a definite surface, as they are mainly composed of gases and liquids. Over 99.86% of the Solar System's mass is in the Sun and nearly 90% of the remaining mass is in Jupiter and Saturn. There is a strong consensus among astronomers[e] that the Solar System has at least nine dwarf planets: Ceres, Orcus, Pluto, Haumea, Quaoar, Makemake, Gonggong, Eris, and Sedna. There are a vast number of small Solar System bodies, such as asteroids, comets, centaurs, meteoroids, and interplanetary dust clouds. Some of these bodies are in the asteroid belt (between Mars's and Jupiter's orbit) and the Kuiper belt (just outside Neptune's orbit).[f] Six planets, seven dwarf planets, and other bodies have orbiting natural satellites, which are commonly called 'moons'. The largest objects that orbit the Sun are the eight planets. In order from the Sun, they are four terrestrial planets (Mercury, Venus, Earth and Mars); two gas giants (Jupiter and Saturn); and two ice giants (Uranus and Neptune). All terrestrial planets have solid surfaces. Inversely, all giant planets do not have a definite surface, as they are mainly composed of gases and liquids. Over 99.86% of the Solar System's mass is in the Sun and nearly 90% of the remaining mass is in Jupiter and Saturn.

PLANETS AND STARS

The sun

The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light and infrared radiation with 10% at ultraviolet energies. It is by far the most important source of energy for life on Earth. The Sun has been an object of veneration in many cultures. It has been a central subject for astronomical research since antiquity.

Mercury

The smallest planet in the Solar System. Its surface is grayish, with an expansive rupes (cliff) system generated from thrust faults and bright ray systems formed by impact event remnants. The surface has widely varying temperature, with the equatorial regions ranging from −170 °C at night to 420 °C during sunlight. In the past, Mercury was volcanically active, producing smooth basaltic plains similar to the Moon. It is likely that Mercury has a silicate crust and a large iron core. Mercury has a very tenuous atmosphere, consisting of solar-wind particles and ejected atoms. Mercury has no natural satellites.

Venus

Venus has a reflective, whitish atmosphere that is mainly composed of carbon dioxide. At the surface, the atmospheric pressure is ninety times as dense as on Earth's sea level. Venus has a surface temperatures over 400 °C , mainly due to the amount of greenhouse gases in the atmosphere. The planet lacks a protective magnetic field to protect against stripping by the solar wind, which suggests that its atmosphere is sustained by volcanic activity. Its surface displays extensive evidence of volcanic activity with stagnant lid tectonics. Venus has no natural satellites.

Earth

Earth is the only place in the universe where life and surface liquid water are known to exist. Earth's atmosphere contains 78% nitrogen and 21% oxygen, which is the result of the presence of life. The planet has a complex climate and weather system, with conditions differing drastically between climate regions. The solid surface of Earth is dominated by green vegetation, deserts and white ice sheets. Earth's surface is shaped by plate tectonics that formed the continental masses. Earth's planetary magnetosphere shields the surface from radiation, limiting atmospheric stripping and maintaining life habitability.

Mars

Mars has a radius about half of that of Earth. Most of the planet is red due to iron oxide in Martian soil, and the polar regions are covered in white ice caps made of water and carbon dioxide. Mars has an atmosphere composed mostly of carbon dioxide, with surface pressure 0.6% of that of Earth, which is sufficient to support some weather phenomena. During the Mars year (687 Earth days), there are large surface temperature swings on the surface between −78.5 °C to 5.7 °C . The surface is peppered with volcanoes and rift valleys, and has a rich collection of minerals. Mars has a highly differentiated internal structure, and lost its magnetosphere 4 billion years ago.

Jupiter

is the biggest and most massive planet in the Solar System. On its surface, there are orange-brown and white cloud bands moving via the principles of atmospheric circulation, with giant storms swirling on the surface such as the Great Red Spot and white 'ovals'. Jupiter possesses a strong enough magnetosphere to redirect ionizing radiation and cause auroras on its poles. As of 2025, Jupiter has 95 confirmed satellites.

Saturn

Saturn has a distinctive visible ring system orbiting around its equator composed of small ice and rock particles. Like Jupiter, it is mostly made of hydrogen and helium. At its north and south poles, Saturn has peculiar hexagon-shaped storms larger than the diameter of Earth. Saturn has a magnetosphere capable of producing weak auroras. As of 2025, Saturn has 274 confirmed satellites.

Uranus

Uranus uniquely among the planets, orbits the Sun on its side with an axial tilt >90°. This gives the planet extreme seasonal variation as each pole points alternately toward and then away from the Sun. Uranus' outer layer has a muted cyan color, but underneath these clouds are many mysteries about its climate, such as unusually low internal heat and erratic cloud formation. As of 2025, Uranus has 28 confirmed satellites.

Neptune

Neptune is the farthest planet from the Sun and is the eighth and smallest planet in the Solar System. Neptune has a deep blue color due to the presence of methane in its atmosphere. Neptune has a faint ring system and 14 known satellites. Neptune has a strong magnetosphere and a complex internal structure. As of 2025, Neptune has 14 confirmed satellites.