Rocky Planets

Rocky Planets

The four planets nearest to the Sun are Mercury, Venus, Earth and Mars. They are made mainly of solid matter, especially rocks of various kinds.

All the rocky planets except Mercury are surrounded by a layer of gases. These gases make up each plant's atmosphere. But Mercury is so close to the Sun that the Sun's rays have blasted away its gases. Without an atmosphere there is nothing to burn up the meteoroids and other space rocks hurtling towards the planet. Over millions of years, these objects have smashed into Mercury's surface, creating many bowl-shaped holes called craters.

Mercury and Venus

The sunny side of Mercury reaches a blistering 450°C (842°F) - almost twice as hot as a household oven at its highest heat. However, on the other side it can be -170°C (-338°F) - almost twice as cold as Earth's coldest place.

Venus's thick, heavy atmosphere traps the Sun's rays so it gets even hotter than Mercury - more than 460°C (860°F). Venus also spins in a different way. When viewed from the Sun, Venus moves in a clockwise direction, while other planets move counter-clockwise. Venus also rotates more slowly than the other planets. One day in Venus would equal 243 Earth days.

The 'Red Planet'

Mars is the planet most like the Earth, although it appears very different. Its surface of dust and rocks has a reddish colour caused by mineral iron oxide, also known as rust. The thin atmosphere of mostly poisonous carbon dioxide causes winds and dust storms. The planet is too cold for water to stay as liquid, so it is thought no living things can exist there. However, scientists believe that billions of years ago there may have been a 'wet period' on Mars that could have sustained life.

Fact brief

Fascinating Fact
• From 1990, the spacecraft Magellan used radar (bounced-back radio waves) to 'see' through the clouds to Venus's surface, showing volcanoes, jagged mountains, valleys, and plains.