Mars is the "red planet" for a very good reason: its surface is made of a thick layer of oxidized iron dust and rocks of the same color. Maybe another name for Mars could be "Rusty." But the ruddy surface does not tell the whole story of the composition of this world.
The dust that covers the surface of Mars is fine like talcum powder. Beneath the layer of dust, the Martian crust consists mostly of volcanic basalt rock. The soil of Mars also holds nutrients such as sodium, potassium, chloride and magnesium. The crust is about 30 miles (50 kilometers) thick.
Mars' crust is thought to be one piece. Unlike Earth, the red planet has no tectonic plates that ride on the mantle to reshape the terrain. Since there is little to no movement in the crust, molten rock flowed to the surface at the same point for successive eruptions, building up into the huge volcanoes that dot the Martian surface.
Mantle and core
Evidence suggests there have been no volcanic eruptions for millions of year, however. The mantle that lies beneath the crust is largely dormant. It is made up primarily of silicon, oxygen, iron, and magnesium and probably has the consistency of soft rocky paste. It is probably about 900 to 1,200 miles (5,400 to 7,200 kilometers) thick, scientists say.
The center of Mars likely has a solid core composed of iron, nickel, and sulfur. It is estimated to be between 1,800 and 2,400 miles (3,000 and 4,000 kilometers) in diameter. The core does not move, and therefore Mars has no magnetic field. Without a magnetic field, radiation bombards the planet making it relatively inhospitable compared to Earth. [Infographic: Inside Planet Mars]
Any life that ever existed on Mars would have had to cope with the radiation, perhaps by thriving underground. While astronomers continue to search for past or present signs of biology on Mars, no convincing evidence has yet been found.
Water and Atmosphere
Mars is too cold for liquid water to exist for any length of time, but features on the surface suggest that water once flowed on Mars. Today, water exists in the form of ice in the soil, and in sheets of ice in the polar ice caps. The average temperature is about minus 80 degrees F (minus 60 degrees C), although they can vary from minus 195 degrees F (minus 125 degrees C) near the poles during the winter to as much as 70 degrees F (20 degrees C) at midday near the equator.
The atmosphere of Mars is too thin to easily support life as we know it. It is about 95 percent carbon dioxide. The extremely thin air on Mars can also become very dusty. Dust from the planet’s surface is routinely kicked up into the atmosphere by giant dust devils— not unlike tornadoes on Earth. At times, the red planet can be partly or wholly consumed by dust storms.
At times, it even snows on Mars. The Martian snowflakes, made of carbon dioxide rather than water, are thought to be about the size of red blood cells.
— Tim Sharp, Reference Editor