Solar System

The Solar System[lower-alpha 3] is the gravitationally bound system of the Sun and the objects that orbit it. The largest of these objects are the eight planets, which in order from the Sun are four terrestrial planets (Mercury, Venus, Earth and Mars); two gas giants (Jupiter and Saturn); and two ice giants (Uranus and Neptune). The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud.

Quick facts: Age, Location, Nearest star, Nearest known pl... ▼

Solar System

Show without caption Show with caption The Sun, planets, moons and dwarf planets[lower-alpha 1] (true color, size to scale, distances not to scale)
Age	4.568 billion years
Location	Local Interstellar Cloud, Local Bubble, Orion–Cygnus Arm, Milky Way
Nearest star	Proxima Centauri (4.2441 ly) Alpha Centauri (4.37 ly)
Nearest known planetary system	Proxima Centauri system (4.2441 ly)
Planetary system
Semi-major axis of outer known planet (Neptune)	30.11 AU (4.5 bill. km; 2.8 bill. mi)
Distance to Kuiper cliff	~30 AU from the Sun
Populations
Stars	1 (Sun)
Known planets	Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Known dwarf planets	Ceres Orcus Pluto Haumea Quaoar Makemake Gonggong Eris Sedna
Known natural satellites	758 (285 planetary 473 minor planetary)[1]
Known minor planets	1,298,410[lower-alpha 2][2]
Known comets	4,586[lower-alpha 2][2]
Identified rounded satellites	19
Orbit about Galactic Center
Invariable-to-galactic plane inclination	60.19° (ecliptic)
Distance to Galactic Center	27,000 ± 1,000 ly
Orbital speed	220 km/s; 136 mi/s
Orbital period	225–250 myr
Star-related properties
Spectral type	G2V
Frost line	≈5 AU[3]
Distance to heliopause	≈120 AU
Hill sphere radius	≈1–3 ly

All four terrestrial planets belong to the inner Solar System (≤ 1.7 AU) and have a solid surface. Inversely, all four giant planets belong to the outer Solar System (≤ 30.5 AU) and do not have a definite surface, as they are mainly composed of gases and liquids. 99.86% of the Solar System's mass is in the Sun and nearly 90% of the remaining mass are in Jupiter and Saturn. There is a strong consensus among astronomers that the Solar System also has nine dwarf planets, which consist of one asteroid-belt object – Ceres; five Kuiper-belt objects – Pluto, Orcus, Haumea, Quaoar, and Makemake; and three scattered-disc objects – Gonggong, Eris, and Sedna.

There are a vast number of smaller objects orbiting the Sun, called small Solar System bodies. This category includes asteroids, comets, centaurs, meteoroids and interplanetary dust clouds. Many of these objects are in the asteroid belt between the orbits of Mars and Jupiter (1.5–4.5 astronomical units, AU), and the Kuiper belt just outside Neptune's orbit (30–50 AU).[lower-alpha 4] Six of the major planets, the six largest possible dwarf planets, and many of the smaller bodies are orbited by natural satellites, commonly called "moons" after Earth's Moon. Two natural satellites, Jupiter's moon Ganymede and Saturn's moon Titan, are larger than Mercury, the smallest terrestrial planet, though they are less massive.

The Sun's stream of charged particles creates the heliosphere, which terminates where the pressure of the solar wind is equal to the surrounding interstellar medium, forming a boundary called the heliopause. The outermost region of the Solar System is the Oort cloud (from 2,000 to 50,000–200,000 AU), the source for long-period comets. The Solar System, which ends at the Sun's sphere of gravitational influence (50,000–200,000 AU), is embedded in the Local Cloud of the interstellar medium and orbits the Galactic Center. The closest star to the Solar System, Proxima Centauri, is 4.25 light years away.