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The
Grand Canyon of Mars - Valles Marineris
This mosaic image of Valles Marineris - colored
to resemble the martian surface - comes from the
Thermal Emission Imaging System (THEMIS), a
visible-light and infrared-sensing camera on
NASA's Mars Odyssey orbiter.
Built from more than 500 daytime infrared
photos, the mosaic shows the whole valley in
more detail than any previous composite photo.
Despite the valley's huge extent - including its
western extension through Noctis Labyrinthus, it
reaches some 3,000 kilometers (2,000 miles) long
- the smallest details visible in the image are
about the size of a football field: 100 meters
(328 feet).
Geologists think Valles Marineris began to open
along geological faults about 3.5 billion years
ago. The faulting was caused by the tectonic
activity that accompanied the growth of the
giant volcanoes in Tharsis, lying just to the
west. As molten rock (magma) pushed into Tharsis
from below, the entire region rose, and the
surrounding crustal rocks stretched and broke
into faults and fractures.
As cracks opened, the ground sank, much as the
keystone in an arch drops when the ends of the
arch move apart. The faulting also opened paths
for subsurface water to escape, undermining the
ground and enlarging the fracture zone. In
countless places, the valley's steep, newly
exposed walls became unstable, causing
landslides that widened the canyon further.
It's not clear when the valley's growth stopped
- and in places even today small landslides
undoubtedly occur. But it appears the main
activity came to a halt roughly 2 billion years
ago.
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