• Differences between the Moon's near and

    From ScienceDaily@1:317/3 to All on Friday, April 08, 2022 22:30:42
    Differences between the Moon's near and far sides linked to colossal
    ancient impact

    Date:
    April 8, 2022
    Source:
    Brown University
    Summary:
    New research shows how the impact that created the Moon's South
    Pole - - Aitken basin is linked to the stark contrast in composition
    and appearance between the two sides of the Moon.



    FULL STORY ==========================================================================
    The face that the Moon shows to Earth looks far different from the one
    it hides on its far side. The nearside is dominated by the lunar mare --
    the vast, dark- colored remnants of ancient lava flows. The crater-pocked
    far side, on the other hand, is virtually devoid of large-scale mare
    features. Why the two sides are so different is one of the Moon's most
    enduring mysteries.


    ==========================================================================
    Now, researchers have a new explanation for the two-faced Moon -- one
    that relates to a giant impact billions of years ago near the Moon's
    south pole.

    A new study published in the journal Science Advancesshows that the
    impact that formed the Moon's giant South Pole-Aitken (SPA) basin would
    have created a massive plume of heat that propagated through the lunar interior. That plume would have carried certain materials -- a suite of rare-Earth and heat- producing elements -- to the Moon's nearside. That concentration of elements would have contributed to the volcanism that
    created the nearside volcanic plains.

    "We know that big impacts like the one that formed SPA would create a
    lot of heat," said Matt Jones, a Ph.D. candidate at Brown University
    and the study's lead author. "The question is how that heat affects
    the Moon's interior dynamics. What we show is that under any plausible conditions at the time that SPA formed, it ends up concentrating these heat-producing elements on the nearside. We expect that this contributed
    to the mantle melting that produced the lava flows we see on the surface."
    The study was a collaboration between Jones and his advisor Alexander
    Evans, an assistant professor at Brown, along with researchers from
    Purdue University, the Lunar and Planetary Science Laboratory in Arizona, Stanford University and NASA's Jet Propulsion Laboratory.

    The differences between the near and far sides of the Moon were first
    revealed in the 1960s by the Soviet Luna missions and the U.S. Apollo
    program. While the differences in volcanic deposits are plain to see,
    future missions would reveal differences in the geochemical composition
    as well. The nearside is home to a compositional anomaly known as the Procellarum KREEP terrane (PKT) -- a concentration of potassium (K),
    rare earth elements (REE), phosphorus (P), along with heat-producing
    elements like thorium. KREEP seems to be concentrated in and around
    Oceanus Procellarum, the largest of the nearside volcanic plains, but
    is sparse elsewhere on the Moon.

    Some scientists have suspected a connection between the PKT and the
    nearside lava flows, but the question of why that suite of elements
    was concentrated on the nearside remained. This new study provides an explanation that is connected to the South Pole-Aitken basin, the second largest known impact crater in the solar system.

    For the study, the researchers conducted computer simulations of how
    heat generated by a giant impact would alter patterns of convection in
    the Moon's interior, and how that might redistribute KREEP material in
    the lunar mantle.

    KREEP is thought to represent the last part of the mantle to solidify
    after the Moon's formation. As such, it likely formed the outermost layer
    of mantle, just beneath the lunar crust. Models of the lunar interior
    suggest that it should have been more or less evenly distributed beneath
    the surface. But this new model shows that the uniform distribution
    would be disrupted by the heat plume from the SPA impact.

    According to the model, the KREEP material would have ridden the wave
    of heat emanating from the SPA impact zone like a surfer. As the heat
    plume spread beneath the Moon's crust, that material was eventually
    delivered en masse to the nearside. The team ran simulations for a
    number of different impact scenarios, from dead-on hit to a glancing
    blow. While each produced differing heat patterns and mobilized KREEP
    to varying degrees, all created KREEP concentrations on the nearside, consistent with the PKT anomaly.

    The researchers say the work provides a credible explanation for one of
    the Moon's most enduring mysteries.

    "How the PKT formed is arguably the most significant open question in
    lunar science," Jones said. "And the South Pole-Aitken impact is one
    of the most significant events in lunar history. This work brings those
    two things together, and I think our results are really exciting."

    ========================================================================== Story Source: Materials provided by Brown_University. Note: Content may
    be edited for style and length.


    ========================================================================== Related Multimedia:
    * Near_and_far_side_of_the_moon,_lunar_mantle ========================================================================== Journal Reference:
    1. Matt J. Jones, Alexander J. Evans, Brandon C. Johnson, Matthew
    B. Weller,
    Jeffrey C. Andrews-Hanna, Sonia M. Tikoo, James
    T. Keane. A South Pole- Aitken impact origin of the lunar
    compositional asymmetry. Science Advances, 2022; 8 (14) DOI:
    10.1126/sciadv.abm8475 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220408142950.htm

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