STANDARD FORM – PLANETS FASTEST PLANET Click a planet to find out more about it. Click the title to start the activity.

The Sun is a star. It contains more than 99.8% of the total mass in the Solar System, with Jupiter having most of the rest. It is about 4,500 million years old and will probably stay almost the same for another 5,000 million years before "dying". All the energy from the Sun is produced in the core by nuclear fusion. It takes about 50 million years for this energy to make its way out to the surface! And then about another 8 minutes for the light to reach the Earth.

Mercury is the closest planet to the Sun. It is quite similar to the Moon, with lots of craters, but it has no moon of its own. Mercury was the Roman god of travel, and the planet probably got its name because it moves so fast across the sky. Only one spacecraft, Mariner 10, has been to Mercury. It flew-by in 1973 and 1974, but only mapped about half of the surface, shown here.

Venus is the second planet out from the Sun. It is the brightest object in the night sky other than the Moon. The first spacecraft to visit Venus was Mariner 2 in 1962, but more than 20 have been in total so far. The planet is covered in very thick cloud. The surface can only be seen using Radar. The temperature at the surface is very high (up to 460 °C). This is because it has a very strong Greenhouse Effect.

Earth is the third planet out from the Sun. It has one very large natural satellite, the Moon. About 70% of the surface is covered in water. It is the only planet known to have life on it.

Mars is the fourth planet out from the Sun, one further out than Earth Sometimes called "the Red Planet", it gets its colour from its red rocks and soil. The surface changes from winter to summer. This was thought to be evidence for plants and other life, but is now known to be enormous dust storms that cover most of the planet. Many spacecraft have been sent to Mars and some, like the Mars Rover missions in 2003, have even landed on the surface, making it the most well known planet in the Solar System other than the Earth itself! It has two small moons called Phobos and Deimos.

Jupiter is the largest planet in the Solar System: You could fit all the other planets inside it at the same time and still have room left! It is a Gas Giant, this means that is does not have a solid surface, but is a huge ball of gas. What we see is the top of the highest clouds. The famous Red Spot (shown to the right) is a single giant storm, first seen over 300 years ago and still going strong! Jupiter was the Roman King of the Gods. As of May 2005, Jupiter is known to have 63 moons.The largest four (Io, Europa, Ganymede and Callisto) were discovered in 1610 by Galileo.

Saturn is the second largest planet in the Solar System after Jupiter. Like Jupiter, it is a Gas Giant and so does not have a solid surface. It is famous for its dramatic and beautiful rings. The rings are not solid, but are made up of many millions of small lumps of ice and rock, varying from a few centimetres to several metres across. These are all orbiting around Saturn together. Although they look very impressive, the rings are only about 1 km thick, compared to 250,000 km in diameter! As of July 2007, Saturn is known to have at least 60 moons (more than any other planet). The largest, Titan, is larger than both Mercury and Pluto.

Uranus, like Jupiter and Saturn, is a Gas Giant and does not have a solid surface. However, it is blue not yellow/orange because it has different chemicals at the top of the clouds because it is colder. Uranus has rings, like Saturn, but they are much thinner and difficult to see. Uranus was the first planet to be discovered in modern times (by William Herschel in 1781). Uranus has 27 known moons (as of May 2005). 22 are very small and most are close to Uranus. The other five (Miranda, Ariel, Umbriel, Titania and Oberon) are larger and further out.

Neptune is a blue Gas Giant like Uranus and is named after the Roman God of the Sea. The dark spot in the image here is a storm like the Great Red Spot on Jupiter. However, the blue storm here has probably already disappeared. Neptune’s winds are the fastest known on any planet, getting as fast as 2000 km per hour. Neptune has twelve small moons and one large one called Triton. Until recently, Neptune was the most distant planet from the Sun, and had been since 1979, but Pluto's orbit crossed Neptunes' on the 11th February 1999 to return to being the most distant planet.

Which is the fastest planet? Planet Orbit Radius (distance from Sun) Length of Year Mercury 5.791 × 107 km 88 Earth days Venus 1.082 × 108 km 225 Earth days Earth 1.496 × 108 km 365.25 Earth days Mars 2.2794 × 108 km 687 Earth days Jupiter 7.7833 × 108 km 11.9 Earth years Saturn 1.4294 × 109 km 29.45 Earth years Uranus 2.871 × 109 km 84.01 Earth years Neptune 4.5043 × 109 km 164.79 Earth years Calculate the speed of each planet in kilometres per second. Assume the planets orbit the sun in a circular path. Use 3 significant figures in your calculations Hint