Our solar system has eight recognized planets, each with its unique characteristics. There are two main types of planets in the solar system -- terrestrial and gas giant. The four planets closest to the sun -- Mercury, Venus, Earth and Mars -- are the terrestrial planets. They are smaller with rocky surfaces and relatively shallow atmospheres. The gas giants -- Jupiter, Saturn, Uranus and Neptune -- are larger planets, but most of this size is attributed to incredibly large atmospheres with small, icy cores.
Mercury is the closest planet to the sun. Its cratered surface can reach upwards of 800 degrees fahrenheit because of its proximity to the sun and its slow rotation. Only slightly larger than Earth's moon, it is the smallest planet in the solar system. It has no moons, no rings, and a very thin atmosphere.
The second planet from the sun, Venus, is slightly smaller than Earth. Because of its relative proximity to Earth, it is the largest planet seen in the night sky. The cratered surface of the planet is hot, with surface temperatures around 900 degrees fahrenheit. Venus has a thick atmosphere of sulfuric acid and carbon dioxide. The density of its atmosphere makes the air pressure 90 times that of Earth's. This makes the planet decidedly inhospitable to life.
Earth, the third planet from the sun and the largest terrestrial planet, is the only planet known to have living beings and the only one with liquid water on its surface. The atmosphere made of mostly nitrogen, oxygen and carbon dioxide is crucial to Earth's ability to support life. The surface of the earth is mostly water, but with large landmasses and a stunning variety of different ecosystems.
Mars, also called the Red Planet, is the solar system's fourth planet. Its surface is characterized by dust storms, large volcanoes and deep valleys. The red color of the surface comes from iron oxide or rust in the soil. Some of the surface features of Mars, such as dry river beds, hint toward water previously existing on the planet. The atmosphere is very thin on Mars, with only 1/100th the air pressure of Earth, and the planet is relatively cold with surface temperatures ranging from -171 to 32 degrees fahrenheit.
Further from the sun, past a ring of asteroids, lies the largest planet in our solar system -- Jupiter -- the first of the gas giant planets. Its characteristic colored cloud patterns are caused by enormous, swirling storms in its atmosphere. The largest and most distinctive of these, the Great Red Spot, is large enough to swallow Earth. The interior of this great planet is mostly hydrogen and helium. Jupiter has 63 moons and a faint ring system.
Saturn, the sixth planet from the sun and the second gas giant, is unique in that an extensive and complex set of rings orbit the planet in a thin band. Saturn is large -- about 9.5 times the radius of Earth. It has 62 moons in its orbit. The interior of Saturn, like Jupiter, is made of mostly hydrogen and helium in liquid form because of the strong pressure there.
While most planets spin on their axis with a slight tilt, the gas giant Uranus spins on a plane with the orbit of the sun. This creates unique seasonal changes. This cold planet is four times the diameter of Earth, and is made of a large atmosphere of methane with a dense core of frozen methane. Uranus has a faint ring system and 27 moons in its orbit.
The blue planet Neptune is the farthest from the sun and, like Uranus, is a very cold place. Because of its distance from the sun, one year on Neptune is 165 Earth years. The large amount of methane in the atmosphere gives the planet its blue color, and the cold interior of the planet is mainly methane ice. It is a relatively large planet. Also like Uranus, it has a diameter roughly four times that of Earth. Thirteen moons and a faint ring system orbit the planet.