The new color images from the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter show an equatorial landscape of hills composed of dozens of alternating layers of dark- and light-toned rocks, and crossed by dark sand dunes.

    Within those layered deposits, the exquisitely detailed images show, there are a series of linear fractures, called joints, that are surrounded by "halos" of light-toned bedrock. In a paper to be published 16 February in the journal Science, researchers argue that the "halos" offer clear evidence of past fluid flow through the bedrock.

    Minerals in the fluid acted like cement to strengthen and bleach the rock, they say. The cemented rock proved more resistant to wind erosion than other features on the canyon walls and floor.It now serves as an exposed record of hydrological activity and offers a promising site to search for evidence of habitable niches in the Martian past.

    Chris H. Okubo, the principal author of the paper said the new images strongly suggest that subsurface fluids -- probably water, liquid carbon dioxide or a combination of the two -- once flowed abundantly in the western Candor Chasma region of Mars.

    Candor Chasma is one of several canyons that make up the great Martian rift valley called Valles Marineris. The rift valley would extend across the United States and is 6 to 7 times deeper than the Grand Canyon in places. It is the deepest gash on any planet in the solar system.

    The linear fractures photographed by HiRISE are hundreds of meters to several kilometers in length. The origin of the joints remains a mystery, Okubo said. But once formed, they provided a pathway for substantial flows from an underground reservoir of some kind. The timing of the flows remains uncertain, Okubo said, but could have occurred many millions or several billions of years ago.

    Related:

    Air on Mars playing game of hide-and-seek?

    BEIJING, Jan. 26 (Xinhuanet) -- Two years of observations by the European Space Agency's Mars Express spacecraft have scientists wondering if air on Mars might be playing a game of hide-and-seek.

    New findings suggest the missing atmosphere of Mars might be stashed away beneath the surface of the planet, rather than having been blown away by solar winds as previously thought. Where the atmosphere went is still unclear.

    "There are different alternatives," said study leader Stas Barabash of the Swedish Institute of Space Physics in Kiruna, Sweden. "One is that it is still stored somewhere on Mars in some hidden reservoir we cannot find."

    Study: sun does not blow water off Mars

    BEIJING, Jan 26. (Xinhuanet) -- New measurements show the solar wind, rather than the sun, blows away the water on Mars, scientists of Sweden and France wrote in the journal Science Friday.

    The dusty red Mars was once covered with lakes, oceans and perhaps rivers, they discovered.

    Though water flows relatively recently on its surface, the European scientists have been trying to find out where all the water on Mars goes and ruled out the sun as the culprit.

    They found ions -- charged particles -- being blown off the planet, not by the sun, but by the solar wind, itself a stream of charged particles.

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