Find out about our outermost planets
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Which are the gas and ice giants?
The ice and gas giants are Jupiter, Saturn, Uranus and Neptune. We call these planets the outer solar system, the inner solar system (Mercury, Venus, Earth and Mars) are mainly made up of rock and called Terrestrial planets.All these planets have some things in common, they all have short and long years compared to Earth. The long years makes sense - the amount of time it takes to orbit the sun will get longer the further away you are but the length of day depends on lots of different factors that may make a planet rotate faster or slower than Earth.- Length of a day (in Earth hours)
- Length of a year (in Earth years)
Although Saturn is famous for it's ring - all the outer planets have rings around them. They are probably bits of debris that get caught in the planets orbit.
What is a gas giant?Gas giants are made of mainly hydrogen and helium. This is the same as stars so large gas giants (such as Jupiter) are sometimes known as failed stars. They are not big enough to become stars on their own but if you could crash 100's of them together, they could get big enough to ignite and become a star.Gas giants do not have a surface, the planets are mainly swirling gases and liquids (the pressure is so great that some of the hydrogen is liquid.) They also have central cores which may be solid or a really thick liquid, even though the surface temperature of gas giants is very cold, the cores are extremely hot.
Saturn and Jupiter are the gas giants of our solar system.
JupiterJupiter is the largest planet in our solar system, it's actually the third most visible object in the solar system so you have probably seen it in the night sky but not realised! Even though it's mainly gas, Jupiter is so big it's mass is 2 1/2 times bigger than all the other planets put together (it's still only 1/1000th of the sun though.)
As it's a gas giant, Jupiter is mainly made of hydrogen and helium so it doesn't have a solid surface but it probably has a rocky core. Even though it's so big, Jupiter is the has the fastest rotation of all the planets - this mean it has the shortest day - which means that it isn't a true sphere, it bulges a little bit at the equator. One strange thing about Jupiter is that has a huge magnetic field, this can make it quiet dangerous for any spacecraft that get near it. Jupiter is famous for it's Red Spot - this is actually a huge storm that has been going on for over a hundred years. Jupiter is also the most likely place for us to find extra terrestrial life, not on the planet itself but there is evidence of a huge ocean under the crust of one of it's moons - Europa.
SaturnSaturn is most famous for it's amazing rings, it isn't the only planet to rings but they are the most striking. There are 7 separate rings which are thought to be made of billions of little pieces of comets, moons and asteroids that were heading towards Saturn but got torn apart by it's gravity. The pieces can be as small as a fleck of dust or as big as a mountain! Saturn is quite a lot smaller than Jupiter and even though it does have a solid core, it is actually less dense (lighter) than water so would float if you could find a big enough bowl of water to put it in. Like Jupiter, Saturn is spinning really really fast. although not quite as fast as Jupiter - a day on Saturn is a few hours long than one on Jupiter - the effect of this spinning affects Saturn more and which makes it look like a ball that's been squished. Saturn has the most moons of any of the planets (82) and, excitingly, two of them, Titan and Enceladus, may be able to support life if we ever need a new home.
The Ice GiantsIce giants are huge plants that are made up of heavier elements than hydrogen and helium that make up the gas giants, mainly as compounds - water, ammonia or methane. All these exist as swirling liquids so ice giants do not have a surface, however they may have a rocky core. The term 'ice' is a bit misleading as there is very little actual ice in these planets, astronomers call elements with boiling points above a certain temperature 'ices' even though they are liquid or gas. The ice giants in our solar system are Uranus and Neptune, they both appear blue/green because of all the methane (natural gas) in their atmospheres.
UranusAs it is so far away, Uranus is the first planet that was discovered using a modern telescope. The other planets are visible from Earth so had been known about for centuries before we knew about Uranus (and Neptune). Uranus is particularly interesting as it rotates in the opposite direction to most other planets - Venus is the only other planet that rotates east to west. BUT that isn't the coolest thing about how Uranus rotates, it is actually on it's side, probably because it collided with something millions of years ago. This means that the poles of Uranus are facing either directly towards or away from the sun so the seasons are really extreme. A Uranian year is 84 Earth years which means that the winters are in total darkness and the summers are in never ending light - and each lasts for 21 years. This also means that despite not being the planet furthest away from the sun, Uranus is the coldest. Uranus was never meant to have it's name, Willian Herschel discovered the planet and wanted to call it Georgium Sidus after King George III but he was overruled and it stuck to convention and was named after a Greek God instead. It does have a rebellious streak though as all it's moons are named after fictional characters from William Shakespeare and Alexander Pope rather than Greek and Roman Gods like the other planets.Uranus has also given it's name to an important Earthly element - Uranium. Uranium was discovered just a few years after Uranus and so was named after it.
NeptuneNeptune was the only planet that was predicted before it was discovered. Astronomers had noticed that Uranus' position was slightly off where it was predicted to be which led them to think there may be another planet beyond it. When they had predicted where it might be, they started looking for it and, hey presto, Neptune was discovered. Neptune, like all ice giants, is made up of water, methane and ammonia however there may be an ocean of super hot water there, the only reason it doesn't boil away is because of the high pressure keeping it locked inside. Neptune would be a very dark place to live, it is so far away from the sun that even when it was the middle of the day and the planet was at it's sunniest, it would look like twilight here on Earth, the sun is about 9 times brighter here than it is on Neptune. Even though it is so far away from the sun, Neptune is the windiest place in the solar system - the winds can get up to a whopping 1,200 miles an hour. Although we don't know a huge amount about Neptune - our probes have only every gone past it once - we do know it has a very interesting moon. Triton is the only large moon in the solar system that rotates in the opposite direction to the planet it orbits, we also know that it is getting warmer but have no idea why!
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