Mars

Rust-red Mars is the fourth planet from the sun. This dry, cold world is about half the size of Earth. Giant volcanoes, deep faults, rock-strewn plains, and dried-up riverbeds mark its surface. Like earth, it has polar ice caps and seasons.

structure and atmosphere this ball of rock and metal is the outermost rocky planet. When it was young and molten, its material differentiated to form a core and layers. the heavy iron sank to the center, and the lighter silicate rocks formed a mantle around the metallic core. the least dense material formed the crust. mars then started to cool and solidify from

THE PLANET'S iNTERiOR

A thick mantle of solid silicate rock surrounds a small metallic core, which probably consists of iron. The mantle was a source of volcanic activity in the past. Above the mantle is a rocky crust just a few dozen miles deep.

small, probably iron core the outside in. the core is probably solid now, since the relatively small size of mars and its distance from the sun would suggest it has cooled more than earth's core.

mars takes almost two earth years to orbit the sun. Its axis of rotation is tilted by 25.2° to the plane of its orbit and, like earth, mars experiences seasons and a day that lasts about 24 hours. Its orbit is more eccentric than earth's; there is a difference of about 26 million miles (42 million km) between its closest and farthest distance from the sun. When closest, it receives 45 percent more solar radiation, which leads to higher surface temperatures.

ATMOSPHERiC COMPOSiTiON

A thin carbon-dioxide rich atmosphere surrounds the planet. Iron oxide dust particles suspended in the atmosphere color it pink. Frozen carbon dioxide and water ice form thin clouds. argon (1.6%)

small, probably iron core

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