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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