The Solar System consists of the Sun and those celestial objects
bound to it by gravity, all of which formed from the collapse of a
giant molecular cloud approximately 4.6 billion years ago. Of the
retinue of objects that orbit the Sun, most of the mass is contained
within eight relatively solitary planets whose orbits are almost
circular and lie within a nearly-flat disc called the ecliptic
plane. The four smaller inner planets, Mercury, Venus, Earth and
Mars, also called the terrestrial planets, are primarily composed of
rock and metal. The four outer planets, Jupiter, Saturn, Uranus and
Neptune, also called the gas giants, are composed largely of
hydrogen and helium and are far more massive than the terrestrials.

The Solar System is also home to two regions populated by smaller
objects. The asteroid belt, which lies between Mars and Jupiter, is
similar to the terrestrial planets as it is composed mainly of rock
and metal. Beyond Neptune’s orbit lie trans-Neptunian objects
composed mostly of ices such as water, ammonia and methane. Within
these two regions, five individual objects, Ceres, Pluto, Haumea,
Makemake and Eris, are recognized to be large enough to have been
rounded by their own gravity, and are thus termed dwarf planets. In
addition to thousands of small bodies in those two regions, various
other small body populations, such as comets, centaurs and
interplanetary dust, freely travel between regions.

The solar wind, a flow of plasma from the Sun, creates a bubble
in the interstellar medium known as the heliosphere, which extends
out to the edge of the scattered disc. The hypothetical Oort cloud,
which acts as the source for long-period comets, may also exist at a
distance roughly a thousand times further than the heliosphere.

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.

The solar system begin with the
Sun, our star, then progresses to the inner planets.

Inner Solar System

- Inner
planets –
Mercury, Venus, Earth, Mars

- Asteroid
belt – Asteroids
are mostly small Solar System bodies composed mainly of refractory
rocky and metallic minerals. Ceres is the largest body in the
asteroid belt and is classified as a dawarf planet.

Outer Solar System

- Outer
planets -
Jupiter, Saturn, Uranus, Neptune,

- Comets -
Comets are small Solar System bodies, typically only a few
kilometres across, composed largely of volatile ices. They have
highly eccentric orbits, generally a perihelion within the orbits of
the inner planets and an aphelion far beyond Pluto.

Trans-Neptunian region

- Kuiper belt –
Pluto, Charon, Haumea and makemake are dward planets that are apart
of the Kuper belt.

- Scattered
disc – the
scattered disc overlaps the Kuiper belt but extends much futher
outwards. Eris is the only dwarf planet in this disc.

Farthest regions

- Heliopause -
The heliosphere is divided into two separate regions. The solar wind
travels at roughly 400 km/s until it collides with the interstellar
wind; the flow of plasma in the interstellar medium. The collision
occurs at the termination shock, which is roughly 80–100 AU from
the Sun upwind of the interstellar medium and roughly 200 AU from
the Sun downwind.

- Oort cloud –
hypothetical Oort cloud is a spherical cloud of up to a trillion icy
objects that is believed to be the source for all long-period
comets. The largest aobject in the Oort cloud is Sedna, likely to be
considered a dwarf planet.

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