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Asked by ZAK.T! to Heather, Helen, Hugh, Jane, Julian on 16 Nov 2014.
Question: what is our solar system made out of?
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Julian Onions answered on 16 Nov 2014:
Most of our solar system is the Sun, it has nearly all the mass, and is made mostly our of hydrogen and helium.
This is similar for the big gas giant planets like Jupiter and Saturn, Neptune and Uranus.
The rocky planets, Mercury, Venus, Earth and Mars dont have much of these gases, as they are too small to hold onto them, so we’re left with the rubbish of the solar systems, the tiny bits that aren’t hydrogen and helium, which is around 2% of the total contents. So we’re sort of the cosmic rubbish pile, being the bits left over the Sun and other big planets didn’t want (although they have some of the rubbish too)!
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Helen Johnson answered on 17 Nov 2014:
We think solar systems form out of large clouds of gas and dust called a nebula. As the cloud comes together under gravity, the centre collapses and heats up to form a star. What’s left is a rotating cloud of material, which gets thinner the faster it rotates. This is called a ‘protoplanetary disk’. We saw one of these in action just recently, a pretty fascinating picture: http://apod.nasa.gov/apod/ap141110.html
Within the disk, some regions are denser than others, and the matter starts to clump together. As the clumps orbit around the star they attract more material because of their gravity. These are the beginnings of planets! Planetesimals towards the centre are rocky, because most of the gas has already been cleared out by the star (so we get planets like Earth), but in the outer parts there is lots of ice and gas left over (to form the ‘gas giant’ planets like Jupiter).
These ‘baby’ planets continue to grow and will collide with each other. Eventually there will be fewer, larger planets which have cleared out their orbits by either absorbing material or tossing it out of the way with gravitational interactions. Now we have a solar system!
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