3. Mars: Young Volcanic Terrain
This region, the same size as the highlands area in slide #2, is on the north flank of the great volcano Elysium Mons, about 800 kilometers south-southeast of the Viking 2 lander site (slide #9). The channel of Hrad Vallis snakes northward (upward) from Elysium Mons. Detailed images show that the surface here is covered with lava flows. In contrast to the southern highlands, most of the northern hemisphere of Mars is young. It has relatively few impact craters because most ancient craters have been covered or erased by more recent geologic activity. For Mars, though, young might mean “only” 2 billion years old, compared to the 4 billion years of the southern highlands.
Lava flow fields like this would not have been thought good places to hunt for traces of martian life, but the martian meteorite ALH 84001 is a volcanic rock and it contains possible fossils. Primitive life grows abundantly in volcanic hot springs, like those at Yellowstone National Park. With this in mind, scientists have proposed searching for life in young volcanic terrains such as this one, in the hope of finding evidence of ancient hot springs or current subsurface thermal activity.
Viking Orbiter mosaic (MDIM), NASA. From 31°N to 36°N and 216°W to 224°W, view approximately 500 kilometers across. Image processing by Brian Fessler and Allan Treiman (Lunar and Planetary Institute).