• Scientists model landscape formation on

    From ScienceDaily@1:317/3 to All on Monday, April 25, 2022 22:30:42
    Scientists model landscape formation on Titan, revealing an Earth-like
    alien world

    Date:
    April 25, 2022
    Source:
    Stanford University
    Summary:
    A new hypothesis reveals that a global sedimentary cycle driven
    by seasons could explain the formation of landscapes on Saturn's
    moon Titan.

    The research shows the alien world may be more Earth-like than
    previously thought.



    FULL STORY ========================================================================== Saturn's moon Titan looks very much like Earth from space, with rivers,
    lakes, and seas filled by rain tumbling through a thick atmosphere. While
    these landscapes may look familiar, they are composed of materials that
    are undoubtedly different -- liquid methane streams streak Titan's icy
    surface and nitrogen winds build hydrocarbon sand dunes.


    ==========================================================================
    The presence of these materials -- whose mechanical properties are
    vastly different from those of silicate-based substances that make up
    other known sedimentary bodies in our solar system -- makes Titan's
    landscape formation enigmatic. By identifying a process that would allow
    for hydrocarbon-based substances to form sand grains or bedrock depending
    on how often winds blow and streams flow, Stanford University geologist
    Mathieu Lapo^tre and his colleagues have shown how Titan's distinct dunes, plains, and labyrinth terrains could be formed.

    Titan, which is a target for space exploration because of its potential habitability, is the only other body in our solar system known to have
    an Earth-like, seasonal liquid transport cycle today. The new model,
    published in Geophysical Research Letters April 25, shows how that
    seasonal cycle drives the movement of grains over the moon's surface.

    "Our model adds a unifying framework that allows us to understand how
    all of these sedimentary environments work together," said Lapo^tre, an assistant professor of geological sciences at Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth). "If we understand how
    the different pieces of the puzzle fit together and their mechanics,
    then we can start using the landforms left behind by those sedimentary processes to say something about the climate or the geological history
    of Titan -- and how they could impact the prospect for life on Titan."
    A missing mechanism In order to build a model that could simulate the
    formation of Titan's distinct landscapes, Lapo^tre and his colleagues
    first had to solve one of the biggest mysteries about sediment on the
    planetary body: How can its basic organic compounds -- which are thought
    to be much more fragile than inorganic silicate grains on Earth --
    transform into grains that form distinct structures rather than just
    wearing down and blowing away as dust?


    ==========================================================================
    On Earth, silicate rocks and minerals on the surface erode into sediment
    grains over time, moving through winds and streams to be deposited
    in layers of sediments that eventually -- with the help of pressure, groundwater, and sometimes heat -- turn back into rocks. Those rocks
    then continue through the erosion process and the materials are recycled through Earth's layers over geologic time.

    On Titan, researchers think similar processes formed the dunes, plains,
    and labyrinth terrains seen from space. But unlike on Earth, Mars, and
    Venus, where silicate-derived rocks are the dominant geological material
    from which sediments are derived, Titan's sediments are thought to be
    composed of solid organic compounds. Scientists haven't been able to demonstrate how these organic compounds may grow into sediment grains that
    can be transported across the moon's landscapes and over geologic time.

    "As winds transport grains, the grains collide with each other
    and with the surface. These collisions tend to decrease grain size
    through time. What we were missing was the growth mechanism that could counterbalance that and enable sand grains to maintain a stable size
    through time," Lapo^tre said.

    An alien analog The research team found an answer by looking at sediments
    on Earth called ooids, which are small, spherical grains most often
    found in shallow tropical seas, such as around the Bahamas. Ooids form
    when calcium carbonate is pulled from the water column and attaches in
    layers around a grain, such as quartz.



    ==========================================================================
    What makes ooids unique is their formation through chemical precipitation, which allows ooids to grow, while the simultaneous process of erosion
    slows the growth as the grains are smashed into each other by waves and
    storms. These two competing mechanisms balance each other out through
    time to form a constant grain size -- a process the researchers suggest
    could also be happening on Titan.

    "We were able to resolve the paradox of why there could have been
    sand dunes on Titan for so long even though the materials are very
    weak, Lapo^tre said. "We hypothesized that sintering -- which involves neighboring grains fusing together into one piece -- could counterbalance abrasion when winds transport the grains." Global landscapes Armed
    with a hypothesis for sediment formation, Lapo^tre and the study co-
    authors used existing data about Titan's climate and the direction
    of wind- driven sediment transport to explain its distinct parallel
    bands of geological formations: dunes near the equator, plains at the mid-latitudes, and labyrinth terrains near the poles.

    Atmospheric modeling and data from the Cassini mission reveal that
    winds are common near the equator, supporting the idea that less
    sintering and therefore fine sand grains could be created there --
    a critical component of dunes. The study authors predict a lull in
    sediment transport at mid-latitudes on either side of the equator,
    where sintering could dominate and create coarser and coarser grains, eventually turning into bedrock that makes up Titan's plains.

    Sand grains are also necessary for the formation of the moon's labyrinth terrains near the poles. Researchers think these distinct crags could
    be like karsts in limestone on Earth -- but on Titan, they would be
    collapsed features made of dissolved organic sandstones. River flow and rainstorms occur much more frequently near the poles, making sediments
    more likely to be transported by rivers than winds. A similar process
    of sintering and abrasion during river transport could provide a local
    supply of coarse sand grains -- the source for the sandstones thought
    to make up labyrinth terrains.

    "We're showing that on Titan -- just like on Earth and what used to be
    the case on Mars -- we have an active sedimentary cycle that can explain
    the latitudinal distribution of landscapes through episodic abrasion
    and sintering driven by Titan's seasons," Lapo^tre said. "It's pretty fascinating to think about how there's this alternative world so far
    out there, where things are so different, yet so similar." Lapo^tre is
    also an assistant professor, by courtesy, of geophysics. Study co-
    authors are from NASA's Jet Propulsion Laboratory (JPL).

    This research was supported by a NASA Solar System Workings grant.


    ========================================================================== Story Source: Materials provided by Stanford_University. Original
    written by Danielle Torrent Tucker. Note: Content may be edited for
    style and length.


    ========================================================================== Related Multimedia:
    * Three_mosaics_of_Titan ========================================================================== Journal Reference:
    1. Mathieu G. A. Lapo^tre, Michael J. Malaska, Morgan L. Cable. The
    Role of
    Seasonal Sediment Transport and Sintering in Shaping Titan's
    Landscapes: A Hypothesis. Geophysical Research Letters, 2022; 49
    (8) DOI: 10.1029/ 2021GL097605 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220425104939.htm

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