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- - - - ==<prosody pitch="medium">Only two spacecraft have ever visited Mercury.</prosody><break time="0.5s" />Owing to its proximity to the Sun, Mercury is a difficult planet to visit. During 1974 and 1975 Mariner 10 flew by Mercury three times, during this time they mapped just under half of the planet’s surface. On August 3rd 2004, the Messenger probe was launched from Cape Canaveral Air Force Station, this was the first spacecraft to visit since the mid 1970’s.
        ==<prosody pitch="medium">Mercury is named for the Roman messenger to the gods.</prosody><break time="0.5s" />The exact date of Mercury’s discovery is unknown as it pre-dates its first historical mention, one of the first mentions being by the Sumerians around in 3,000 BC.
        ==<prosody pitch="medium">Mercury has an atmosphere (sort of).</prosody><break time="0.5s" />Mercury has just 38% the gravity of Earth, this is too little to hold on to what atmosphere it has which is blown away by solar winds. However while gases escape into space they are constantly being replenished at the same time by the same solar winds, radioactive decay and dust caused by micrometeorites
        ==<prosody pitch="medium">Mercury is only the second hottest planet.</prosody><break time="0.5s"/>Despite being further from the Sun, Venus experiences higher temperatures. The surface of Mercury which faces the Sun sees temperatures of up to 427°C, whilst on the alternate side this can be as low as -173°C. This is due to the planet having no atmosphere to help regulate the temperature.
        ==<prosody pitch="medium">Mercury is the most cratered planet in the Solar System.</prosody><break time="0.5s"/>Unlike many other planets which “self-heal” through natural geological processes, the surface of Mercury is covered in craters. These are caused by numerous encounters with asteroids and comets. Most Mercurian craters are named after famous writers and artists. Any crater larger than 250 kilometres in diameter is referred to as a Basin. The Caloris Basin is the largest impact crater on Mercury covering approximately 1,550 km in diameter and was discovered in 1974 by the Mariner 10 probe. #
  - - - ==<prosody pitch="medium">Venus is also known as the Morning Star and the Evening Star.</prosody><break time="0.5s" />Early civilisations thought Venus was two different bodies, called Phosphorus and Hesperus by the Greeks, and Lucifer and Vesper by the Romans. This is because when its orbit around the Sun overtakes Earth’s orbit, it changes from being visible after sunset to being visible before sunrise. Mayan astronomers made detailed observations of Venus as early as 650 AD.
        ==<prosody pitch="medium">Venus is the hottest planet in our solar system. </prosody><break time="0.5s" />The average surface temperature is 462 °C, and because Venus does not tilt on its axis, there is no seasonal variation. The dense atmosphere of around 96.5 percent carbon dioxide traps heat and causes a greenhouse effect.
        ==<prosody pitch="medium">A detailed study of Venus finished in 2015.</prosody><break time="0.5s" />In 2006, the Venus Express space craft was sent into orbit around Venus by the European Space Agency, and sent back information about the planet. Originally planned to last five hundred Earth days, the mission was extended several times before the craft was finally deorbited in 2015. More than 1,000 volcanoes or volcanic centres larger than 20 km have been found on the surface of Venus.
        ==<prosody pitch="medium">The Russians sent the first mission to Venus.</prosody><break time="0.5s" />The Venera 1 space probe was launched in 1961, but lost contact with base. The USA also lost their first probe to Venus, Mariner 1, although Mariner 2 was able to take measurements of the planet in 1962. The Soviet Union’s Venera 3 was the first man-made craft to land on Venus in 1966.
        ==<prosody pitch="medium">At one point it was thought Venus might be a tropical paradise. </prosody><break time="0.5s" />The dense clouds of sulphuric acid surrounding Venus make it impossible to view its surface from outside its atmosphere. It was only when radio mapping was developed in the 1960s that scientists were able to observe and measure the extreme temperatures and hostile environment. It is thought Venus did once have oceans but these evaporated as the planets temperature increased. #
  - - - ==<prosody pitch="medium">Mars and Earth have approximately the same landmass.</prosody><break time="0.5s"/>Even though Mars has only 15% of the Earth’s volume and just over 10% of the Earth’s mass, around two thirds of the Earth’s surface is covered in water. Martian surface gravity is only 37% of the Earth’s (meaning you could leap nearly three times higher on Mars).
        ==<prosody pitch="medium">Mars is home to the tallest mountain in the solar system.</prosody><break time="0.5s"/>Olympus Mons, a shield volcano, is 21km high and 600km in diameter. Despite having formed over billions of years, evidence from volcanic lava flows is so recent many scientists believe it could still be active.
        ==<prosody pitch="medium">Only 18 missions to Mars have been successful.</prosody><break time="0.5s"/>As of September 2014 there have been 40 missions to Mars, including orbiters, landers and rovers but not counting flybys. The most recent arrivals include the Mars Curiosity mission in 2012, the MAVEN mission, which arrived on September 22, 2014, followed by the Indian Space Research Organization’s MOM Mangalyaan orbiter, which arrived on September 24, 2014. The next missions to arrive will be the European Space Agency’s ExoMars mission, comprising an orbiter, lander, and a rover, followed by NASA’s InSight robotic lander mission, slated for launch in March 2016 and a planned arrival in September, 2016.
        ==<prosody pitch="medium">Mars has the largest dust storms in the solar system.</prosody><break time="0.5s"/>They can last for months and cover the entire planet. The seasons are extreme because its elliptical (oval-shaped) orbital path around the Sun is more elongated than most other planets in the solar system. # #
  - - - ==<prosody pitch="medium">Saturn can be seen with the naked eye.</prosody><break time="0.5s"/>It is the fifth brightest object in the solar system and is also easily studied through binoculars or a small telescope.
        ==<prosody pitch="medium">Saturn was known to the ancients, including the Babylonians and Far Eastern observers.</prosody><break time="0.5s"/>It is named for the Roman god Saturnus, and was known to the Greeks as Cronus.
        ==<prosody pitch="medium">Saturn is the flattest planet.</prosody><break time="0.5s"/>Its polar diameter is 90% of its equatorial diameter, this is due to its low density and fast rotation. Saturn turns on its axis once every 10 hours and 34 minutes giving it the second-shortest day of any of the solar system’s planets.
        ==<prosody pitch="medium">Saturn orbits the Sun once every 29.4 Earth years.</prosody><break time="0.5s"/>Its slow movement against the backdrop of stars earned it the nickname of “Lubadsagush” from the ancient Assyrians. The name means “oldest of the old”.
        ==<prosody pitch="medium">Saturn’s upper atmosphere is divided into bands of clouds.</prosody><break time="0.5s"/>The top layers are mostly ammonia ice. Below them, the clouds are largely water ice. Below are layers of cold hydrogen and sulfur ice mixtures. #
  - - - ==<prosody pitch="medium">The Great Red Spot is a huge storm on Jupiter.</prosody><break time="0.5s"/>It has raged for at least 350 years. It is so large that three Earths could fit inside it.
        ==<prosody pitch="medium">Jupiter’s interior is made of rock, metal, and hydrogen compounds.</prosody><break time="0.5s"/>Below Jupiter’s massive atmosphere (which is made primarily of hydrogen), there are layers of compressed hydrogen gas, liquid metallic hydrogen, and a core of ice, rock, and metals.
        ==<prosody pitch="medium">Jupiter’s moon Ganymede is the largest moon in the solar system.</prosody><break time="0.5s"/>Jupiter’s moons are sometimes called the Jovian satellites, the largest of these are Ganymeade, Callisto Io and Europa. Ganymeade measures 5,268 km across, making it larger than the planet Mercury.
        ==<prosody pitch="medium">Jupiter has a thin ring system.</prosody><break time="0.5s"/>Its rings are composed mainly of dust particles ejected from some of Jupiter’s smaller worlds during impacts from incoming comets and asteroids. The ring system begins some 92,000 kilometres above Jupiter’s cloud tops and stretches out to more than 225,000 km from the planet. They are between 2,000 to 12,500 kilometres thick.
        ==<prosody pitch="medium">Eight spacecraft have visited Jupiter.</prosody><break time="0.5s"/>Pioneer 10 and 11, Voyager 1 and 2, Galileo, Cassini, Ulysses, and New Horizons missions. The Juno mission is its way to Jupiter and will arrive in July 2016. Other future missions may focus on the Jovian moons Europa, Ganymede, and Callisto, and their subsurface oceans. #
  - - - ==<prosody pitch="medium">Uranus was officially discovered by Sir William Herschel in 1781.</prosody><break time="0.5s"/>It is too dim to have been seen by the ancients. At first Herschel thought it was a comet, but several years later it was confirmed as a planet. Herscal tried to have his discovery named “Georgian Sidus” after King George III. The name Uranus was suggested by astronomer Johann Bode. The name comes from the ancient Greek deity Ouranos.
        ==<prosody pitch="medium">Uranus turns on its axis once every 17 hours, 14 minutes.</prosody><break time="0.5s"/>The planet rotates in a retrograde direction, opposite to the way Earth and most other planets turn.
        ==<prosody pitch="medium">Uranus makes one trip around the Sun every 84 Earth years.</prosody><break time="0.5s"/>During some parts of its orbit one or the other of its poles point directly at the Sun and get about 42 years of direct sunlight. The rest of the time they are in darkness.
        ==<prosody pitch="medium">Uranus is often referred to as an “ice giant” planet.</prosody><break time="0.5s"/>Like the other gas giants, it has a hydrogen upper layer, which has helium mixed in. Below that is an icy “mantle, which surrounds a rock and ice core. The upper atmosphere is made of water, ammonia and the methane ice crystals that give the planet its pale blue colour. #
  - - - ==<prosody pitch="medium">Neptune has a very active climate.</prosody><break time="0.5s"/>Large storms whirl through its upper atmosphere, and high-speed winds track around the planet at up 600 meters per second. One of the largest storms ever seen was recorded in 1989. It was called the Great Dark Spot. It lasted about five years.
        ==<prosody pitch="medium">Neptune has a very thin collection of rings.</prosody><break time="0.5s"/>They are likely made up of ice particles mixed with dust grains and possibly coated with a carbon-based substance.
        ==<prosody pitch="medium">Neptune has 14 moons.</prosody><break time="0.5s"/>The most interesting moon is Triton, a frozen world that is spewing nitrogen ice and dust particles out from below its surface. It was likely captured by the gravitational pull of Neptune. It is probably the coldest world in the solar system.
        ==<prosody pitch="medium">Only one spacecraft has flown by Neptune.</prosody><break time="0.5s"/>In 1989, the Voyager 2 spacecraft swept past the planet. It returned the first close-up images of the Neptune system. The NASA/ESA Hubble Space Telescope has also studied this planet, as have a number of ground-based telescopes. #
  - - - ==<prosody pitch="medium">Pluto is one third water.</prosody><break time="0.5s"/>This is in the form of water ice which is more than 3 times as much water as in all the Earth’s oceans, the remaining two thirds are rock. Pluto’s surface is covered with ices, and has several mountain ranges, light and dark regions, and a scattering of craters.
        ==<prosody pitch="medium">Pluto is smaller than a number of moons.</prosody><break time="0.5s"/>These are Ganymede, Titan, Callisto, Io, Europa, Triton, and the Earth’s moon. Pluto has 66% of the diameter of the Earth’s moon and 18% of its mass. While it is now confirmed that Pluto is the largest dwarf planet for around 10 years it was thought that this was Eris.
        ==<prosody pitch="medium">Pluto has a eccentric and inclined orbit.</prosody><break time="0.5s"/>This takes it between 4.4 and 7.3 billion km from the Sun meaning Pluto is periodically closer to the Sun than Neptune.
        ==<prosody pitch="medium">Pluto has been visited by one spacecraft.</prosody><break time="0.5s"/>The New Horizons spacecraft, which was launched in 2006, flew by Pluto on the 14th of July 2015 and took a series of images and other measurements. New Horizons is now on its way to the Kuiper Belt to explore even more distant objects.
        ==<prosody pitch="medium">Pluto’s location was predicted by Percival Lowell in 1915.</prosody><break time="0.5s"/>The prediction came from deviations he initially observed in 1905 in the orbits of Uranus and Neptune.
        ==<prosody pitch="medium">Pluto sometimes has an atmosphere.</prosody><break time="0.5s"/>When Pluto elliptical orbit takes it closer to the Sun, its surface ice thaws and forms a thin atmosphere primarily of nitrogen which slowly escapes the planet. It also has a methane haze that overs about 161 kilometres above the surface. The methane is dissociated by sunlight into hydrocarbons that fall to the surface and coat the ice with a dark covering. When Pluto travels away from the Sun the atmosphere then freezes back to its solid state.
        
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