Terrestrial planets. Artwork showing the four terrestrial (rocky) planets: Earth (bottom right),Mars (lower left),Venus (upper centre) and Mercury (upper right). These four are the nearest planets to the Sun,and are made up largely of rock. By contrast,the four main outer planets,Jupiter,Saturn,Uranus and Neptune,are made up mainly of gases. Mars' surface is red due to the extensive deserts of red sand which cover much of the planet. Venus is covered by a permanent cloud layer which traps heat,raising temperatures to over 400 degrees Celsius. Mercury has no atmosphere and is riddled with craters. The planets are not shown to scale |