The Solar System consists of the Sun and those celestial objects bound to it by gravity: the eight planets and five dwarf planets, their 173 known moons, and billions of small bodies. The small bodies include asteroids, icy Kuiper belt objects, comets, meteoroids, and interplanetary dust.
The charted regions of the Solar System comprise the Sun, four terrestrial inner planets, the asteroid belt, four gas giant outer planets, and finally the Kuiper belt and the scattered disc. The hypothetical Oort cloud may also exist at a distance roughly a thousand times beyond these regions.
The solar wind, a flow of plasma from the Sun, permeates the Solar System, creating a bubble in the interstellar medium known as the heliosphere, which extends out to the middle of the scattered disc.
In order of their distances from the Sun, the eight planets are:
- Mercury (57,900,000 km)
- Venus (108,000,000 km)
- Earth (150,000,000 km)
- Mars (228,000,000 km)
- Jupiter (779,000,000 km)
- Saturn (1,430,000,000 km)
- Uranus (2,880,000,000 km)
- Neptune (4,500,000,000 km)
As of mid-2008, five smaller objects are classified as dwarf planets, all but the first of which orbit beyond Neptune. These are:
- Ceres (415,000,000 km, in the asteroid belt; formerly classed as the fifth planet)
- Pluto (5,906,000,000 km, formerly classified as the ninth planet)
- Haumea (6,450,000,000 km)
- Makemake (6,850,000,000 km)
- Eris (10,100,000,000 km)
Six of the planets and three of the dwarf planets are orbited by natural satellites, usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.