• Does Mars Have Rings? Not Right Now, But Maybe One Day

    From baalke@1:2320/100 to sci.space.news on Mon Mar 20 20:21:59 2017
    From Newsgroup: sci.space.news


    https://www.jpl.nasa.gov/news/news.php?feature=6781

    Does Mars Have Rings? Not Right Now, But Maybe One Day
    Jet Propulsion Laboratory
    March 20, 2017

    As children, we learned about our solar system's planets by certain characteristics
    -- Jupiter is the largest, Saturn has rings, Mercury is closest to the
    sun. Mars is red, but it's possible that one of our closest neighbors
    also had rings at one point and may have them again someday.

    That's the theory put forth by NASA-funded scientists at Purdue University, Lafayette, Indiana, whose findings were published in the journal Nature Geoscience. David Minton and Andrew Hesselbrock developed a model that suggests that debris that was pushed into space from an asteroid or other
    body slamming into Mars around 4.3 billion years ago alternates between becoming a planetary ring and clumping together to form a moon.

    One theory suggests that Mars' large North Polar Basin or Borealis Basin
    -- which covers about 40 percent of the planet in its northern hemisphere
    -- was created by that impact, sending debris into space.

    "That large impact would have blasted enough material off the surface
    of Mars to form a ring," Hesselbrock said.

    Hesselbrock and Minton's model suggests that as the ring formed, and the debris slowly moved away from the Red Planet and spread out, it began
    to clump and eventually formed a moon. Over time, Mars' gravitational
    pull would have pulled that moon toward the planet until it reached the
    Roche limit, the distance within which a planet's tidal forces will break apart a celestial body that is held together only by gravity.

    Phobos, one of Mars' moons, is getting closer to the planet. According
    to the model, Phobos will break apart upon reaching the Roche limit, and become a set of rings in roughly 70 million years. Depending on where
    the Roche limit is, Minton and Hesselbrock believe this cycle may have repeated between three and seven times over billions of years. Each time
    a moon broke apart and reformed from the resulting ring, its successor
    moon would be five times smaller than the last, according to the model,
    and debris would have rained down on the planet, possibly explaining enigmatic sedimentary deposits found near Mars' equator.

    "You could have had kilometer-thick piles of moon sediment raining down
    on Mars in the early parts of the planet's history, and there are enigmatic sedimentary deposits on Mars with no explanation as to how they got there," Minton said. "And now it's possible to study that material."

    Other theories suggest that the impact with Mars that created the North
    Polar Basin led to the formation of Phobos 4.3 billion years ago, but
    Minton said it's unlikely the moon could have lasted all that time. Also, Phobos would have had to form far from Mars and would have had to cross through the resonance of Deimos, the outer of Mars' two moons. Resonance occurs when two moons exert gravitational influence on each other in a repeated periodic basis, as major moons of Jupiter do. By passing through
    its resonance, Phobos would have altered Deimos' orbit. But Deimos' orbit
    is within one degree of Mars' equator, suggesting Phobos has had no effect
    on Deimos.

    "Not much has happened to Deimos' orbit since it formed," Minton said.
    "Phobos passing through these resonances would have changed that."

    "This research highlights even more ways that major impacts can affect
    a planetary body," said Richard Zurek of NASA's Jet Propulsion Laboratory, Pasadena, California. He is the project scientist for NASA's Mars Reconnaissance
    Orbiter, whose gravity mapping provided support for the hypothesis that
    the northern lowlands were formed by a massive impact.

    Minton and Hesselbrock will now focus their work on either the dynamics
    of the first set of rings that formed or the materials that have rained
    down on Mars from disintegration of moons.

    For more information about NASA missions investigating Mars, visit:

    https://mars.nasa.gov/

    News Media Contact
    Guy Webster
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-6278
    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

    Steve Tally / Emil Venere
    Purdue University, West Lafayette, Ind.
    765-494-9809 / 765-494-4709
    steve@purdue.edu / venere@purdue.edu

    Writer: Brian Wallheimer

    2017-075

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