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Solar System

The Solar System[d] is the gravitationally bound system of the Sun and the objects that orbit it.[11] It was 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.

For other uses, see Solar System (disambiguation).

Age

4.568 billion years[b]

Sun

758[D 3]

1,368,528[D 4]

4,591[D 4]

G2V

~5 AU[5]

30.07 AU[D 5] (Neptune)

50–70 AU[3][4]

detected at 120 AU[6]

1.1 pc (230,000 AU)[7] – 0.865 pc (178,419 AU)[8]

~60°, to the ecliptic[c]

24,000–28,000 ly
[9]
720,000 km/h (450,000 mi/h)[10]

~230 million years[10]

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 Solar System is constantly flooded by the Sun's charged particles, the solar wind, forming the heliosphere. Around 75–90 astronomical units from the Sun,[g] the solar wind is halted, resulting in the heliopause. This is the boundary of the Solar System to interstellar space. 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. Both stars belong to the Milky Way galaxy.

(0.31–0.59 AU from the Sun)[D 6] is the smallest planet in the Solar System. Its surface is greyish, with an expansive rupes (cliff) system generated from thrust faults and bright ray systems formed by impact event remnants.[91] In the past, Mercury was volcanically active, producing smooth basaltic plains similar to the Moon.[92] It is likely that Mercury has a silicate crust and a large iron core.[93][94] Mercury has a very tenuous atmosphere, consisting of solar-wind particles and ejected atoms.[95] Mercury has no natural satellites.[96]

Mercury

(0.72–0.73 AU)[D 6] 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.[97] Venus is the hottest planet, with surface temperatures over 400 °C (752 °F), mainly due to the amount of greenhouse gases in the atmosphere.[98] 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.[99] Its surface displays extensive evidence of volcanic activity with stagnant lid tectonics.[100] Venus has no natural satellites.[101]

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

(30.3–48.1 AU), is in the same 2:3 orbital resonance with Neptune as Pluto, and is the largest such object after Pluto itself.[204] Its eccentricity and inclination are similar to Pluto's, but its perihelion lies about 120° from that of Pluto. Thus, the phase of Orcus's orbit is opposite to Pluto's: Orcus is at aphelion (most recently in 2019) around when Pluto is at perihelion (most recently in 1989) and vice versa.[205] For this reason, it has been called the anti-Pluto.[206][207] It has one known moon, Vanth.[208]

Orcus

Pluto

(34.6–51.6 AU) was discovered in 2005.[211] It is in a temporary 7:12 orbital resonance with Neptune.[204] Haumea possesses a ring system, two known moons named Hiʻiaka and Namaka, and rotates so quickly (once every 3.9 hours) that it is stretched into an ellipsoid. It is part of a collisional family of Kuiper belt objects that share similar orbits, which suggests a giant impact on Haumea ejected fragments into space billions of years ago.[212]

Haumea

(38.1–52.8 AU), although smaller than Pluto, is the largest known object in the classical Kuiper belt (that is, a Kuiper belt object not in a confirmed resonance with Neptune). Makemake is the brightest object in the Kuiper belt after Pluto. Discovered in 2005, it was officially named in 2009.[213] Its orbit is far more inclined than Pluto's, at 29°.[214] It has one known moon, S/2015 (136472) 1.[215]

Makemake

(41.9–45.5 AU) is the second-largest known object in the classical Kuiper belt, after Makemake. Its orbit is significantly less eccentric and inclined than those of Makemake or Haumea.[204] It possesses a ring system and one known moon, Weywot.[216]

Quaoar

Interplanetary spaceflight

Lists of geological features of the Solar System

List of gravitationally rounded objects of the Solar System

List of Solar System extremes

List of Solar System objects by size

Outline of the Solar System

 – Phrase used to remember the planets of the Solar System

Planetary mnemonic

. Encyclopædia Britannica. Vol. 25 (11th ed.). 1911. pp. 157–158.

"Solar System" 

If the Moon were only 1 Pixel: A Tediously Accurate Map of the Solar System (web based scroll map scaled to the Moon being 1 pixel)

NASA's Eyes on the Solar System

NASA's Solar System Exploration

NASA's Solar System Simulator