Why Planets Are Different Colours

Why do the planets have different colours?
The answer is that the planets are different colors because they are made of different materials. Planets have the colours that they have because of what they are made of and how their surfaces or atmospheres reflect and absorb sunlight.
Mercury has a dark grey, rocky surface which is covered with a thick layer of dust. The surface is thought to be made up of igneous silicate rocks and dust. Venus is entirely covered with a thick carbon dioxide atmosphere and sulphuric acid clouds which give it a light yellowish appearance. Earth shows its blue oceans and white clouds as well as its green and brownish land. Mars is covered with a fine dust which contains iron oxide (rust). This gives Mars its orange colour. Jupiter is a giant gas planet with an outer atmosphere that is mostly hydrogen and helium with small amounts of water droplets, ice crystals, ammonia crystals, and other elements. Clouds of these elements create shades of white, orange, brown and red. Saturn is also a giant gas planet with an outer atmosphere that is mostly hydrogen and helium. Its atmosphere has traces of ammonia, phosphine, water vapor, and hydrocarbons giving it a yellowish-brown color. Uranus is a gas planet which has a lot of methane gas mixed in with its mainly hydrogen and helium atmosphere. This methane gas gives Uranus a greenish blue colour. Neptune also has some methane gas in its mainly hydrogen and helium atmosphere, giving it a bluish color. Pluto (now classified as a dwarf planet) - there are no pictures of Pluto which give us a good view of its surface yet, because it is too far away. Pluto may be covered in ice.
2. How many planets are there in our solar system?
Our solar system has nine planets and one star: the Sun. In order from the Sun out, the planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. A popular mnemonic used to remember the planets in order is: My Very Educated Mother Just Served Us Nine Pizzas.
3. How did the solar system form?
The planets, asteroids and comets in the Solar System are loose particles left over from the formation of the Sun. Originally the gas and dust which would become the Sun was the core of a cloud much larger than the Solar System, probably several light years across; where 1 light year is equal to approximately 10,000,000,000,000 kilometers (or 6 trillion miles). The core was slowly rotating at first, but as it collapsed it spun faster, like a spinning ice-skater pulling in their arms. The rotation prevented the core's equator from collapsing as fast as the poles, so the core became a spinning disc.
Gas and dust in the disc spiralled gradually in to the center, where it accumulated to form the Sun. But because dust is denser than gas, some of the dust settled to the mid-plane of the disc. These dust particles stuck together to make clumps, then clumps stuck together to make rocks, then rocks collided to make planets. In the case of the `gas giant' planets, Jupiter, Saturn, Uranus and Neptune, the rocky cores were massive enough to also attract some of the gas. The outer layers of these planets are made up of hydrogen and other gases.
So the Sun is the collapsed core of an interstellar gas cloud, and the planets, asteroids and comets are small lumps of dust which stayed in orbit instead of spiralling into the Sun. The planets all formed within a very short period, probably a few million years, about five billion years ago. Within that short time, no-one knows for sure which of them formed first. Maybe the inner planets formed first and were dragged by the spiralling gas so they are now closest to the Sun; or maybe the outer planets formed first, and the inner ones are small because they didn't have a long time to grow.
4. How old is the solar system?
The solar system is about 4.5 billion years old.
The different compositions of the outer planets give them their different colors. Jupiter and Saturn appear yellowish and reddish because of the polysulfides and phosphorus in their atmospheres. Uranus and Neptune have more methane and ammonia in their atmospheres and so they appear bluish. Notice that while Jupiter, Saturn and Neptune have much structure in their atmospheres, Uranus looks very smooth with no obvious features. What does this tell us about the interior of Uranus compared to the other giant planets?

|Planets |
|[pic] sun |
|[pic]mercury |
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|[pic]Venus |
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|[pic]Earth |
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|[pic]Mars |
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|[pic]Jupiter |
|[pic]Saturn |
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|[pic]Uranus |
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|[pic]Neptune |

www.coolcosmos.ipac.caltech.edu/cosmic_kids