Answer to Question 1
When the crust of a planet is strained, it may break, producing faults and rift valleys. Near the Tharsis region on Mars is a great valley, Valles Marineris, named after the Mariner 9 spacecraft that first photographed it. The valley is a block of crust that has dropped downward along parallel faults. Erosion and landslides have further modified the valley into a great canyon. It is four times deeper, nearly ten times wider, and more than ten times longer than the Grand Canyon. The number of craters in the valley indicates that it is 1 to 2 billion years old, placing its origin sometime before the end of the most active volcanism in the Tharsis region.
Answer to Question 2
Unlike Mercury or Venus, Mars has moons. Small and irregular in shape, Phobos (28 23 20 km in diameter) and Deimos (16 12 10 km) are almost certainly captured asteroids. These moons are so small they cannot pull themselves into spherical shape. Phobos and Deimos are not just small; they are tiny. An athletic astronaut who could jump 2 m (6 ft) high on Earth could jump almost 3 km (2 mi) on Phobos. These moons are so small that any interior heat would have leaked away very quickly, and there is no evidence of any internally driven geologic activity on either object.
A very high-resolution texture of the planet Mars
True-color view of Mars seen through NASA's Hubble Space Telescope in 1999
Mars's average distance from the Sun is roughly 230 million km (1.5 AU) and its orbital period
the comet Encke riding along its pebbly trail of debris (long diagonal line) between the orbits of M
Sunlight on Mars is dimmer than on Earth. This photo of a Martian sunset was imaged by Mars Pathfind
Similar Rock Outcrops on Mars and Earth