Valles Marineris 

The most prominent area of the Valles Marineris up close (Copyright Calvin J. Hamilton)

The most dramatic feature of Mars' incredible landscape is the great canyon system known as the Valles Marineris. Named in honor of the Mariner 9, these canyons stretch over 3,000 miles (5,000 kilometers) across the surface. That's almost one fifth of the way around Mars! In certain areas of this great canyon, the depth reaches up to 4 miles (6 kilometers) deep and 430 miles (700 kilometers) across. The Earth's Grand Canyon is a tiny stream compared to this.

Forming in the very early history of Mars, the Valles Marineris formed from faults occurring along the surface of the planet, followed by water erosion. The significance of the canyon is the fact that though there currently are no bodies of water present on the surface of Mars, the hundreds of channels strongly suggest that Mars was once very abundant in moisture and that there once may have been a thick atmosphere. The presence of water could have been perfect conditions for life though no evidence has found it to be so.

A landslide taking place on the Valles Marineris (Copyright Calvin J. Hamilton).