Surface composition

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A predominant feature of the Martian surface is the iron oxide-rich dust known as regolith, giving the planet its characteristic red color. This dust is very fine and the result of years of meteorite impacts pulverizing the Martian surface spreading dust around the planet. This dust is blown globally by storms, creating massive seasonal dust storms that can last for months.

Rock formations on the surface is primarily composed of basalt - a consequence of the extensive lava flows that once existed as a result of ancient geological activity. Analysis of soil samples collected by the Viking landers in 1976 indicate iron-rich clays consistent with weathering of basaltic rocks.

Panorama taken on the rim of Erebus crater

There is also evidence the Martian surface may be more silica-rich than the basalt created by lava flows, similar to andesitic rocks found on Earth (rock which crystallizes from silicate minerals at intermediate temperatures).

Mars has twice as much iron oxide in its outer layers as Earth does, despite their similar origin (meteorite impacts). This is due to the geologically active (and hotter) Earth transporting much of the surface iron deep below the terrestrial surface. Mars does not have this geological advantage to produce heat, so the iron remains in the Martian regolith, giving Mars its red glow.