• Mars Rover Curiosity Examines Possible Mud Cracks

    From baalke@1:2320/100 to sci.space.news on Thu Feb 16 21:10:41 2017
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    http://www.jpl.nasa.gov/news/news.php?feature=6721

    Mars Rover Curiosity Examines Possible Mud Cracks
    Jet Propulsion Laboratory
    January 17, 2017

    Scientists used NASA's Curiosity Mars rover in recent weeks to examine
    slabs of rock cross-hatched with shallow ridges that likely originated
    as cracks in drying mud.

    "Mud cracks are the most likely scenario here," said Curiosity science
    team member Nathan Stein. He is a graduate student at Caltech in Pasadena, California, who led the investigation of a site called "Old Soaker," on
    lower Mount Sharp, Mars.

    If this interpretation holds up, these would be the first mud cracks -- technically called desiccation cracks -- confirmed by the Curiosity mission. They would be evidence that the ancient era when these sediments were deposited included some drying after wetter conditions. Curiosity has
    found evidence of ancient lakes in older, lower-lying rock layers and
    also in younger mudstone that is above Old Soaker.

    "Even from a distance, we could see a pattern of four- and five-sided
    polygons that don't look like fractures we've seen previously with Curiosity," Stein said. "It looks like what you'd see beside the road where muddy
    ground has dried and cracked."

    The cracked layer formed more than 3 billion years ago and was subsequently buried by other layers of sediment, all becoming stratified rock. Later,
    wind erosion stripped away the layers above Old Soaker. Material that
    had filled the cracks resisted erosion better than the mudstone around
    it, so the pattern from the cracking now appears as raised ridges.

    The team used Curiosity to examine the crack-filling material. Cracks
    that form at the surface, such as in drying mud, generally fill with windblown dust or sand. A different type of cracking with plentiful examples found
    by Curiosity occurs after sediments have hardened into rock. Pressure
    from accumulation of overlying sediments can cause underground fractures
    in the rock. These fractures generally have been filled by minerals delivered by groundwater circulating through the cracks, such as bright veins of
    calcium sulfate.

    Both types of crack-filling material were found at Old Soaker. This may indicate multiple generations of fracturing: mud cracks first, with sediment accumulating in them, then a later episode of underground fracturing and
    vein forming.

    "If these are indeed mud cracks, they fit well with the context of what
    we're seeing in the section of Mount Sharp Curiosity has been climbing
    for many months," said Curiosity Project Scientist Ashwin Vasavada of
    NASA's Jet Propulsion Laboratory in Pasadena. "The ancient lakes varied
    in depth and extent over time, and sometimes disappeared. We're seeing
    more evidence of dry intervals between what had been mostly a record of long-lived lakes."

    Besides the cracks that are likely due to drying, other types of evidence observed in the area include sandstone layers interspersed with the mudstone layers, and the presence of a layering pattern called cross-bedding. This pattern can form where water was flowing more vigorously near the shore
    of a lake, or from windblown sediment during a dry episode.

    Scientists are continuing to analyze data acquired at the possible mud
    cracks and also watching for similar-looking sites. They want to check
    for clues not evident at Old Soaker, such as the cross-sectional shape
    of the cracks.

    The rover has departed that site, heading uphill toward a future rock-drilling location. Rover engineers at JPL are determining the best way to resume
    use of the rover's drill, which began experiencing intermittent problems
    last month with the mechanism that moves the drill up and down during drilling.

    Curiosity landed near Mount Sharp in 2012. It reached the base of the
    mountain in 2014 after successfully finding evidence on the surrounding
    plains that ancient Martian lakes offered conditions that would have been favorable for microbes if Mars has ever hosted life. Rock layers forming
    the base of Mount Sharp accumulated as sediment within ancient lakes billions of years ago.

    On Mount Sharp, Curiosity is investigating how and when the habitable
    ancient conditions known from the mission's earlier findings evolved into conditions drier and less favorable for life. For more information about Curiosity, visit:

    http://mars.jpl.nasa.gov/msl

    News Media Contact
    Guy Webster
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-6278 / 818-393-9011
    guy.webster@jpl.nasa.gov

    Laurie Cantillo / Dwayne Brown
    NASA Headquarters, Washington
    202-358-1077 / 202-358-1726
    laura.l.cantillo@nasa.gov / dwayne.c.brown@nasa.gov

    2017-009

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