• Cassini Finds Saturn Moon Enceladus May Have Tipped Over

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    https://www.jpl.nasa.gov/news/news.php?feature=6860

    Cassini Finds Saturn Moon May Have Tipped Over
    Jet Propulsion Laboratory
    May 30, 2017

    Saturn's icy, ocean-bearing moon Enceladus may have tipped over in the
    distant past, according to recent research from NASA's Cassini mission. Researchers with the mission found evidence that the moon's spin axis
    -- the line through the north and south poles -- has reoriented, possibly
    due to a collision with a smaller body, such as an asteroid.

    Examining the moon's features, the team showed that Enceladus appears
    to have tipped away from its original axis by about 55 degrees -- more
    than halfway toward rolling completely onto its side. "We found a chain
    of low areas, or basins, that trace a belt across the moon's surface that
    we believe are the fossil remnants of an earlier, previous equator and
    poles," said Radwan Tajeddine, a Cassini imaging team associate at Cornell University, Ithaca, New York, and lead author of the paper.

    The area around the icy moon's current south pole is a geologically active region where long, linear fractures referred to as tiger stripes slice
    across the surface. Tajeddine and colleagues speculate that an asteroid
    may have struck the region in the past when it was closer to the equator.
    "The geological activity in this terrain is unlikely to have been initiated
    by internal processes," he said. "We think that, in order to drive such
    a large reorientation of the moon, it's possible that an impact was behind
    the formation of this anomalous terrain."

    In 2005, Cassini discovered that jets of water vapor and icy particles
    spray from the tiger stripe fractures -- evidence that an underground
    ocean is venting directly into space from beneath the active south polar terrain.

    Whether it was caused by an impact or some other process, Tajeddine and colleagues think the disruption and creation of the tiger-stripe terrain caused some of Enceladus' mass to be redistributed, making the moon's
    rotation unsteady and wobbly. The rotation would have eventually stabilized, likely taking more than a million years. By the time the rotation settled down, the north-south axis would have reoriented to pass through different points on the surface -- a mechanism researchers call "true polar wander."

    The polar wander idea helps to explain why Enceladus' modern-day north
    and south poles appear quite different. The south is active and geologically young, while the north is covered in craters and appears much older. The moon's original poles would have looked more alike before the event that caused Enceladus to tip over and relocate the disrupted tiger-stripe terrain to the moon's south polar region.

    The results were published in the online edition of the journal Icarus
    on April 30, 2017.

    The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the mission for
    NASA's Science Mission Directorate, Washington. JPL designed, developed
    and assembled the Cassini orbiter.

    More information about Cassini:

    https://www.nasa.gov/cassini

    https://saturn.jpl.nasa.gov

    News Media Contact
    Preston Dyches
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-394-7013
    preston.dyches@jpl.nasa.gov

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