Solar System 101 | National Geographic

- Our

solar

system

is one of more than 500 known

solar

system

s in the entire Milky Way. The solar system emerged about 4.5 billion years ago, when a cloud of interstellar gas and dust collapsed, giving rise to a solar nebula, a rotating disk of material that collided to form the solar system. The solar system is located in the Orion star cluster in the Milky Way. Only 15% of the stars in the galaxy host planetary systems, and one of those stars is our own sun. Eight planets revolve around the sun. The planets are divided into two categories, according to their composition, terrestrial and Jovian.

The terrestrial planets, including Mercury, Venus, Earth, and Mars, are made primarily of rocky material. Their surfaces are solid, they have no ring systems, they have very few or no moons, and they are relatively small. The smallest and closest to the sun is Mercury, which has the shortest orbit in the solar system at approximately three Earth months. Venus is the hottest planet, with temperatures up to 867 degrees Fahrenheit, due to a carbon dioxide atmosphere and extensive lava flows. Next to this world of fire there is a world of water, the Earth. This planet's water systems help create the only known environment in the universe capable of supporting life.

The last of the terrestrial planets, Mars, could also have supported life about 3.7 billion years ago, when the planet had a watery surface and a humid atmosphere. Beyond the four terrestrial planets of the inner solar system are the Jovian planets of the outer solar system. The Jovian planets include the gas giants Jupiter and Saturn and the ice giants Uranus and Neptune. Gas giants are predominantly made of helium and hydrogen, and ice giants also contain rock, ice, and a liquid mixture of water, methane, and ammonia. The four Jovian planets have multiple moons, sport ring systems, have no solid surface, and are immense.

The largest Jovian is also the largest planet in the solar system, Jupiter. Nearby is Saturn, the second largest planet in the solar system. Its characteristic rings are wide enough to fit between the Earth and the Moon, but are barely a kilometer thick. Beyond Saturn are the ice giants, Uranus and Neptune. The slightly largest of these ice giants, Uranus, is famous for spinning on its side. Next to Uranus is Neptune, the outermost planet in the solar system, and also one of the coldest. Orbiting the terrestrial planets is the asteroid belt, a flat disk of rocky objects, filled with debris from the formation of the solar system.

From microscopic dust particles to the largest known object, the dwarf planet Ceres. Another disk of space debris lies much further away and orbits the Jovian planets, the icy Kuiper Belt. In addition to asteroids, the Kuiper Belt is also home to dwarf planets, such as Pluto, and is the birthplace of many comets. Beyond the Kuiper Belt lies the Oort Cloud, a vast spherical collection of icy debris. It is considered the edge of the solar system since it is where the sun's gravitational and physical influences end. Our solar system's particular configuration of planets and other celestial objects, all orbiting a life-giving star, makes it a special place to call home.