The Salor System
The Solar System is the gravitationally bound system of the Sun and the objects that orbit it, either directly or indirectly,including the eight planets and five dwarf
planets as defined by the International Astronomical
Union (IAU). Of the objects that orbit the Sun directly,
the largest eight are the planets, with the remainder
being smaller objects, such as dwarf planets and small
Solar System bodies. Of the objects that orbit the Sun
indirectly—the moons—two are larger than the
smallest planet, Mercury.The Solar System formed
4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority
of the system's mass is in the Sun, with the majority of
the remaining mass contained in Jupiter. The four
smaller inner planets, Mercury, Venus, Earth and Mars,
are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the
terrestrials. The two largest, Jupiter and Saturn, are gas
giants, being composed mainly
of hydrogen and helium; the two outermost
planets, Uranus and Neptune, are ice giants, being
composed mostly of substances with relatively high
melting points compared with hydrogen and helium,
called volatiles, such as water, ammonia and methane.
All eight planets have almost circular orbits that lie
within a nearly flat disc called the ecliptic.
