Our solar system consists of a star - the Sun - with nine planets under its gravitational influence. Each planet is spinning on its own axis as it orbits the Sun. The planets are different from each other and are in different orbits although they all move around the Sun in the same direction. The four inner planets (Mercury, Venus, Earth, Mars) are known as terrestrial planets. Of the remaining five planets (Jupiter, Saturn, Uranus, Neptune, Pluto) that spin in wider orbits, further away from the Sun, four are known as gas giants because they are huge, dense balls of hydrogen and other gases. Pluto, the furthest away from the sun is tiny and cold and perhaps is not truly a planet.

Here is some basic information about each one, including Earth.

Is the planet closest to the Sun
Completes an orbit of the Sun every 88 Earth days
A waterless, airless world, heavily cratered.
Virtually no atmosphere but some argon, helium and neon
Mercury has a magnetic field and is so dense for its small size that scientists think that it is mostly iron. It is seen as either a "Morning Star" or an "Evening Star". Pluto is the only planet smaller than Mercury.

The second planet from the Sun
Completes an orbit of the Sun every 224.7 Earth days
The surface has mountains and plains
Atmosphere of mostly carbon dioxide but clouds contain sulphuric acid and water
Venus is the planet that passes closest to Earth as they both orbit the Sun. The planet surface is shrouded by clouds which move around the planet very fast producing constant strong winds. Like Mercury, Venus is seen either as a "Morning Star" or an "Evening Star".

The third planet from the Sun
Completes an orbit of the Sun every 365.26 Earth days
A world of oceans and continents, with polar caps
Atmosphere is nitrogen and oxygen with clouds of water vapor
Earth is the only planet of our Sun known to have organic life. From space it appears as a bright blue and white sphere. It appears blue because 75 percent of its surface is water, and white because 50 percent of its surface is covered by clouds.

The fourth planet from the Sun
Completes an orbit of the Sun every 687 Earth days (1.9 yrs)
The surface is dry and cratered, has volcanoes and canyons
Atmosphere is thin; mostly carbon dioxide with some nitrogen
Mars is the outermost of the four terrestrial planest. It has a reddish color (and so is sometimes called the Red Planet) because of the iron oxide (rust) in its soil. Olympus Mons is an inactive volcano as tall as Mount Everest. There are huge canyons one of which is four times deeper that Earth's Grand Canyon. The planet is very cold and has dust storms whipped by hurricane force winds. Mars has two satellites, Deimos and Phobos.

The fifth planet from the Sun
Completes an orbit of the Sun every 4,332.6 Earth days (11.86 yrs)
Surface is ocean of liquid hydrogen
Atmosphere is thick and is mostly hydrogen, with some helium and traces of methane, water and ammonia.
Jupiter is the largest planet in our solar system - it is 11 times bigger than Earth. As Jupiter spins its thick clouds tend to form bands and give the planet its red-brown-white banded appearance. Jupiter's Great Red Spot was first observed about 300 years ago and appears to be a permanent hurricane. This planet has 16 moons (satellites). The four largest were described by Galileo. Ganymede, the largest of these four, is the largest moon in our solar system, larger than the planets Pluto and Mercury.

The sixth planet from the Sun
Completes an orbit of the Sun every 10,759.2 Earth days (29.5 yrs)
The surface is probably liquid and solid hydrogen
Atmosphere is mostly hydrogen with some helium
Saturn is the second largest planet after Jupiter. It has a pale yellow color, and very dramatic rings containing ice crystals rotate around the planet. Tremendously strong winds blow constantly at the equator. Saturn has at least 15 moons most of them small and composed of rock and ice. Titan, the largest appears to be the only moon in our solar system to have an atmosphere.

The seventh planet from the Sun
Completes an orbit of the Sun every 30,685.4 Earth days (84 yrs)
The surface is probably a liquid or slushy hydrogen "crust"
Atmosphere is hydrogen, helium and methane; very clear with no clouds.
Uranus, barely visible in Earth's night sky, was not discovered until 1781. It has a faintly greenish color due perhaps to the methane in its atmosphere. It has faint rings and 5 moons.

The eighth planet from the Sun
Completes an orbit of the Sun every 60,189 Earth days (164.8 yrs)
The surface is probably a slushy hydrogen "crust"
Atmosphere is hydrogen and helium
Neptune was discovered in 1846. It has as a pale bluish color from space and its atmosphere often looks hazy. The planet is very cold but probably has a hot core. It has at least eight moons. Two (Triton and Nereid) were first observed from Earth and six others were observed by Voyager 2.

The ninth planet from the Sun
Completes an orbit of the Sun every 90,465 Earth days (247.7 yrs)
Is a ball of frozen gases
Frozen methane has been detected
Pluto was discovered in 1930 and is about half the size of Earth's moon. It has one known moon, Charon, which was discovered in 1978. Some scientists think that although we call Pluto a planet, it was perhaps once a moon of Neptune and was pulled out of its orbit by the pull from some other celestial body

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