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Images: When mars was a wetland

Spectacular images from Mars orbiter give scientists clues about the history of water on the Red Planet.
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1 of 6 Andy Smith/ZDNet

Mawrth region

A set of images from NASA's Mars orbiter--including clay deposits and huge gullies--may give new insight into what the surface of Mars was like when it was a much wetter planet.

It may look like the inside of an abalone shell at first glance, but this is an image of the surface of Mars, composed from infrared, red and blue-green images captured by NASA's High Resolution Imaging Science Experiment (HiRISE) camera earlier this month. The camera is one of six science instruments aboard the Mars Reconnaissance Orbiter, which arrived at Mars in March and has revealed remarkable new details of the planet's past and present environments.

Researchers are particularly interested in clues that these new images may provide about Mars' past life as a wet planet. Scientists think the brighter areas in this image (of Mawrth Vallis, one of the oldest valleys on Mars) may be rich in clay, an important key to understanding the history of water on Mars because the formation of clay minerals requires that rocks be exposed to liquid water for a long period of time.

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Mawrth Vallis spectrometer

These are four renderings of an image of an area south of Mawrth Vallis that was taken by another instrument aboard the Mars orbiter. The image was compared to measurements of various minerals, and the bottom two renderings at left show clay deposits rich in iron and aluminum.

The type of clay formed is determined by the composition of the rock in the area, as well as the temperature, acidity and salt content of the water. The mission of the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars) spectrometer that created these images is to find identifying characteristics of aqueous and hydrothermal deposits on the planet and then map the geography and composition of the Martian surface.

In this exercise, for example, scientists were able to spot locations where clay and rocks rich in the same mineral existed.

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Terra Sirenum crater

Another feature helping scientists understand the history of water on Mars is the presence of enormous gullies. Most of these gullies are found on the walls of craters in the southern hemisphere, where they remain in shadows for much of the Martian winter accumulating frost.

This is one such crater, located in the Terra Sirenum, pictured here by the Mars orbiter's Context Camera. The HiRISE camera explored the same area, giving incredible colored detail of crater walls.

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Terra Sirenum gullies

This close-up shot of a crater wall has enough detail that it is possible to see variations in color even in the shadows of the deep gullies.

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Polar cap

This is a composite image of Mars' northern polar cap, taken while instruments were being tested before heading into the orbiter's "primary science phase," which is set to begin the first week of November. This is a mosaic of four images taken at midnight, 6 a.m., noon and 6 p.m., made possible by the fact that the sun shines on the pole all day long during the summer.

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Chasma Boreale

This is a CRISM image of a giant valley called the Chasma Boreale that is several miles deep and juts into the edge of the northern polar cap by about 250 miles. The top view is a near-true-color representation, and the bottom view, which conveys strength of the spectral signature of ice, shows where ice is present. The bright white areas are rich in ice; the dark areas are not.

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