Mercury is the closest planet to the Sun and moves at 200,000 Km/hr and has the greatest temperature variations in the solar system. It takes only 88 days to orbit the sun but in that time only experiences about two days during this time. It is too close to the sun to be safely imaged by the Hubble Space Telescope and has only been visited by the Mariner 10 in 1974-1975.
Venus is the second planet from the Sun with a day taking longer than its year. Its reflective clouds of sulphuric acid make Venus the third brightest object in the sky. Its atmosphere of carbon dioxide is 90 times denser than Earth’s and global warming leads to an average surface temperature hot enough to melt lead.
Earth is the only known place in the universe to sustain life. It is often known as the blue planet because it is covered in approximately 71% water. The core of the planet is made of molten iron on which huge plates of land float.
Mars is often known as the red planet because its surface is covered in a compound called Iron Oxide (more commonly known as rust). It shows many geological signs of once having water which suggests that there may have once been life. Mars has the largest volcano in the solar system, Olympus Mons, which is three times the size of Mount Everest.
Jupiter is the largest of the planets and the first of the gas giants. It is mostly made of hydrogen and helium and if it had been much larger it would have become a star. The characteristic ‘red spot’ is actually a giant storm that has been raging for over 300 years. It is so large that three earths would fit inside it. Jupiter has 57 moons, 4 of these are so large they can be seen with binoculars. These 4 Galilean moons are Io, Europa, Callisto and Ganymede.
Saturn is famous for its bright rings (which were discovered by Christian Huygens in 1659) and whilst they look incredibly delicate they are up to 1.5km thick. Saturn has 50 moons, the largest moon Titan is the second largest in the solar system (second only to Ganymede) and holds its own atmosphere. Saturn has a very low density, so low that if you were to put it in a large enough bathtub it would float on the water.
Uranus, the first planet to be discovered in modern times. Sir William Herschel, an amateur astronomer observed the planet on March 13th 1781 from a terraced house in Bath. He proposed that it be dedicated to the King and called ‘Georgium Sidus - ‘George’s Star’ -but tradition prevailed and Uranus, the father of the Roman god Saturn, was chosen. Unlike most planets, Uranus has its south pole pointing almost directly at the Sun. Until Voyager 2 visited the planet in January 1986 only 5 moons were known to exist. Now we know of 27 moons, nearly all named after Shakespearean charcters.
Neptune, predicted to exist by the English astronomer and mathematician John Couch Adams when aged 24, was discovered in 1846. Neptune’s blue colour is caused by the absorption of red light by atmospheric methane. Due to the highly eccentric orbit of Pluto, Neptune is, at some times, further from the Sun than Pluto. Voyager 2 visited the planet in 1989 and is the source of most of our knowledge of the planet.
In 2006 it was decided that Pluto was too small to be a planet and it was demoted to a dwarf planet. It is one of several dwarf planets in our solar system. The largest of which, Sierras, is in the asteroid belt between Mars and Jupiter. Despite being no longer considered a planet it does have a moon, Charon.