The solar system is a planetary system which consists of the Sun and 8 planets (according to Weintraub (2014) Pluto was excluded in 2006) and other cosmic objects like asteroids and comets. It was formed 4.6 billion years ago as a result of gravitational collapse.
All the planets are divided into two groups: inner (Mercury, Venus, Earth and Mars) and outer planets, also known as Giant planets (Jupiter, Saturn, Uranus and Neptune). Also, there is a belt of asteroids between these groups.All inner planets have the same characteristic: like planetary core composed of metals and mantle composed of silicates, the low number of satellites and tectonic relief details as volcanoes and rifts. In comparison with outer planets, we can find a lot of differences: Outer planets are a lot bigger and heavier that inner ones (for example the smallest planet in the outer system – Uranus in 14.6 times heavier than the biggest planet in the inner system – Earth).All inner planets have almost the same density, but outer planets density is a lot smaller due to their chemical composition: according to Dreibus (1984) “…inner planets are composed of metals and silicates“ and outer are almost composed of gases.
So all inner planets got a hard surface and outer planets got no hard surface.Inner planets have no or few satellites (for example Earth has just one, Mars has 2 satellites). But outer planets have a lot of satellites. The exact number of satellites is still changing. Inner planets don’t have rings system, but outer planets have ring systems. All inner planets have a slow rotation speed around own axes and fast rotation around the Sun, and the outer planets are contrariwise with fast rotation around own axes and slow rotation around the Sun.
27th International Geological Congress (1984.). Geochemisrty and cosmochemistry. Retrieved from http://books.google.com.ua/books?id=chn7iBJttcsC&printsec=frontcover&hl=ru&source=gbs_vpt_buy#v=onepage&q&f=false