Mamers Valles is a trough that winds for nearly 1,000 kilometers (600 miles) through the ragged highlands of Arabia Terra on Mars, before it empties onto the vast northern lowlands in Deuteronilus Mensae. In the section seen here, about halfway along its course, the valley averages 25 km (15 miles) wide, and its floor lies 1,200 meters (4,000 feet) below the rim.
Scientists think the linear features on the valley bottom are telling a tale of flowing ice covered with a layer of rock.
This image, taken by the Thermal Emission Imaging System (THEMIS), combines images taken in daytime at both infrared and visible wavelengths. It shows daytime ground temperatures using false colors - warmer areas appear in reddish tints, while colder ones are bluer. Ground temperatures are controlled both by the nature of the surface materials and by solar heating. Slopes that face the Sun more directly become warmer, while those turned away are cooler. In addition, surfaces mantled with fine-grain particles (such as dust or fine sand) respond quicker to solar heating, but more cohesive and rocky material stays cooler.
While Mamers Valles dates from the early Hesperian period in Mars' history - about 3.8 billion years ago - the valley floor contains far younger material, perhaps only a few million years old or less. This material is relatively uncratered, and its lineations show that it has flowed from the valley walls toward the channel's center. Then, after merging with the debris from the channel's other side, it flowed along the valley in a downstream direction.
How much ice this lineated fill contains is the focus of scientific debate. Earlier views held that the valley fill was mostly rock with some ice that collected as water slowly infiltrated through the cracks and voids in the debris. More recently, however, many scientists have concluded that the ice is a lot more plentiful, with perhaps a relatively thin covering of rocky debris. If so, these features would be the Martian equivalent of valley glaciers found on Earth, especially in the Dry Valleys of Antarctica and on Baffin and Ellesmere Islands in the Canadian Arctic.