8. Mars: the red planet
Towering volcanoes, immense canyons
Eons of volcanic activity
When Mariner 9 and Viking 1 and 2 surveyed Mars in the 1970s, they revealed a mind-boggling world with kaleidoscopic beauty and variety. They replaced the bleak, drab, Moon-like view of a frozen, lifeless Mars, obtained during the partial, fleeting glimpses of previous spacecraft, with a new picture of a dynamic, living planet. Powerful forces have molded the face of Mars at an unsuspected scale, including giant volcanoes and immense canyon-lands that dwarf their terrestrial counterparts.
As Mariner 9 settled into orbit around Mars, in November 1971, the planet was buried beneath a global dust storm. After circling the planet for a couple of months, the winds abated, the dust settled, and the spacecraft watched four high mountains emerge from the pall, each with craters at their summit.
The volcanoes are perched on top of a vast uplift, known as the Tharsis bulge, which straddles the ancient uplands and lowland plains near the equator and overlies them both. The Tharsis bulge extends more than 2.5 million meters across, and it was formed roughly 2 billion years ago, after the division between the uplands and lowlands. Olympus Mons, the tallest mountain in the solar system, lies on the western edge of the Tharsis bulge. Three other tall volcanoes, named Arsia Mons, Pavonis Mons and Ascraeus Mons, crown Tharsis. They run diagonally across the equator along a ridge known as Tharsis Montes.
These other three volcanoes are smaller than Olympus, but still much larger than any terrestrial volcano. With their gently sloping flanks and roughly circular summit calderas, the Martian volcanoes resemble the shield volcanoes of Hawaii, such as Mauna Loa, which has a similar slope but one third the height and one twentieth the volume of Olympus Mons. Such volcanoes are formed by the repeated eruption of lava that cascades down the flanks in thousand of individual flows.
The turmoil associated with the formation of the Tharsis uplift and associated volcanoes opened up a network of vast canyons that are collectively known as Valles Marineris (Valleys of the Mariner). The colossal system of interconnected canyons, or chasmata, extends down the eastern flanks of the Tharsis bulge and along the Martian equator for 4 million meters, one-fourth the way around the planet. In places the chasms are as wide and deep, as Mount Everest is high. Their formation may be similar in origin to the rift valley in Africa, but on a much vaster scale. For Mars, it was as if a cosmic sculptor was trying to split the planet asunder.
Valles Marineris originates close to the summit of the Tharsis uplift, at Syria Planum, where the surface expansion and consequent stretching has produced the intricately fractured Noctis Labyrinthus (Labyrinth of the Night). As the name suggests, it is a maze of short, deep gashes intersecting at all angles.
Further east the depressions become deeper, wider and more continuous. In the middle section of Valles Marineris they branch into three parallel canyons, the Ophir, Candor and Melas Chasmata, which are separated by intervening ridges. These canyons connect with the single long Coprates Chasma, which runs eastward and joins Eos Chasma. Yet further east the canyons become shallower, with evidence of past water flow, and finally the canyons terminate in the jumbled, blocky region called the Chaotic Terrain.
(page 7 of 10)
Copyright 2010, Professor Kenneth R. Lang, Tufts University