Planets

	Introduction The Earth is part of the Sun’s family of planets, known as the Solar System. The Sun itself is a star and only looks so bright to us because it is so close, compared to other stars in the universe. There are nine giant planets, including Earth, and thousands of dwarf planets and asteroids in the Solar System and they are all controlled by the Sun. The larger planets are made up mostly of gases and ice with rocky cores and the smaller, inner, principle planets are more solid. The Earth is the only planet able to support life. Mercury Mercury was named after the Roman messenger of the gods. It is heavily cratered and looks a bit like the surface of the moon. We know no life could survive on Mercury because the atmosphere is so thin it is hardly detectable and the temperature ranges from blisteringly hot during the day, to way below freezing during the night. Most of our knowledge of Mercury comes mainly from the 1974-5 Mariner probe. The Messenger probe launched in August 2004 will enter Mercury’s orbit in 2011, collecting data for one Earth year. Average distance from the Sun: 57,910,000km (35,980,000miles) Length of year: 88 Earth days Diameter: 4,878km (3,031miles) Average temperature: Day 800°F (427°C) Night -300°F (-183°C) Venus Venus is named after the Roman goddess of love and is the hottest planet in the Solar System. It’s about the same size as Earth, but it rotates in a retrograde (backwards) direction and has a much thicker atmosphere; standing on the surface of Venus would feel like standing 1km down under the sea on Earth! Until 1962, when Mariner 2 passed by, it was thought that there were oceans on this most brilliant of planets. We now know that Venus is far too hot to have water on the surface; it’s covered in deadly volcanoes and was probably shaped by the movement of tectonic plates. Average distance from the Sun: 108,200,000km (67,230,000miles) Length of year: 225 Earth days Diameter: 12,102km (7520miles) Average temperature: 896°F (480°C) Earth Earth is the third planet from the Sun and the only one in the Solar System not to be named after an ancient god or goddess. It is also the only planet in the universe that is known to support life. 70% of the Earth’s surface is covered in water and it has a relatively steady temperature. Earth is geologically active - its core is hotter than the surface of the Sun and it is constantly experiencing earthquakes, volcanoes and climate changes. The tilt of the planet’s axis is what gives Earth its changing seasons and why there are vast expanses of ice at either pole. Average distance from the Sun: 149,600,000km (92,960,000miles) Length of year: 365.26 Earth days Diameter: 12,756km (7,926miles) Average temperature: 59°F (15°C) Mars The Romans named the planet Mars after their god of war. From the 1960s, the United States and the former Soviet Union spent vast amounts of time and money developing the technology required to be the first to get to Mars. The atmosphere of Mars is quite different from that of Earth. It is composed primarily of carbon dioxide with small amounts of other gases. The current understanding of the interior of Mars suggests that it probably features a thin crust, similar to Earth's, alongside a mantle and a core. Average distance from the Sun: 227,940,000km (141,550,740miles) Length of year: 686.98 Earth days Diameter: 6,794 km (4,221.6 miles) Average temperature: -81°F (-63°C) Jupiter Jupiter takes its name from the king of the Roman gods and for good reason - because it’s the biggest planet in the Solar System. It’s 1300 times the size of Earth, but is made almost entirely of gases, swirling in continuous electrical storms and hurricanes. Its most famous storm - known as the Great Red Spot - has been raging for almost 400 years! Jupiter’s core is extremely magnetic and it has the strongest gravitational pull of any planet, sucking in asteroids, meteors and comets as they pass. At just under ten hours long, Jupiter has the shortest day of all the planets. Average distance from the Sun: 778,400,000km (483,700,000miles) Length of year: 11.9 Earth years Diameter: 142,980km (88,846miles) Average temperature: -238°F (-150°C) Saturn Saturn is named after the Roman god of agriculture and is often described as the most beautiful object in the sky. Saturn's famous rings, which are made from billions of particles of rock and ice, are even visible from Earth with a telescope. Saturn is sixth in line from the sun and the second largest planet in the Solar System. Like Jupiter, Saturn is made almost entirely of gas and its globe is flattened because of its rapid rotation. Saturn has the most moons of any of the planets, twenty-five or more, and one of these - Titan - is thought to be similar to Earth before life began. Average distance from the Sun: 1,427,000,000km (886,700,000miles) Length of year: 29.5 Earth years Diameter: 120,536km (74,901miles) Average temperature: -202°F (-130°C) Uranus Uranus was named after the Greek god of the heavens. It wasn’t discovered until 1781, after the development of the telescope. Uranus is a giant ball of gas about four times the size of Earth and is seventh in line from the Sun. It is the only planet to spin on its side, which means it rolls around in its orbit and has very strange days and seasons. Sometimes the north pole of Uranus points to the Sun and sometimes the south pole does. Its surface is pale blue, mainly because of the high methane content of its gases, and it is mostly featureless. Average distance from the Sun: 2,875,000,000km (1,786,000,000miles) Length of year: 84 Earth years Diameter: 51,118km (31,765 miles) Average temperature: -353°F (-214°C) Neptune Neptune is named after the Roman god of the sea and its main moon, Triton, is named after the three-pronged spear the god carried. Neptune is often seen as Uranus’ twin planet; they are more or less the same size, both blue in colour and formed by similar gases. The fastest winds in the Solar System were recorded on Neptune at 2,000km/h (1,240miles/h). At points during its orbit, Neptune passes Pluto and becomes the furthest planet from the Sun. We haven’t seen it pass through a complete orbit since it was discovered in 1846, because it takes 165 years! Average distance from the Sun: 4,504,000,000 km (2,800,000,000 miles) Length of year: 165 Earth years Diameter: 49,528km (30,775 miles) Average temperature: -364°F (-220°C) Pluto Pluto is named after the Greek god of the underworld. It’s the only planet to be discovered in the twentieth century; no one knew it existed until 1930! This is hardly surprising when you remember that Pluto is the furthest planet from the Sun, apart from 20 years during its orbit, when Neptune takes over. Pluto is the most mysterious of all the planets. It is thought to be made of gas and ice, but we can’t be sure because no probe has ever made it that far. Even the strongest telescope on Earth has difficulty seeing any of Neptune’s detail. Average distance from the Sun: 5,915,000,000km (3,675,000,000miles) Length of year: 248 Earth years Diameter: 2,300km (1,429miles) Average temperature: -382°F (-230°C)