over the origin of large-scale polygons (hundreds of meters to
kilometers in diameter) on Mars remains active even after several
decades of detailed observations. Similarity in geometric patterns on
Mars and Earth has long captured the imagination. In this new article
from GSA Today, geologists at The University of Texas at Austin examine
these large-scale polygons and compare them to similar features on
Earth’s seafloor, which they believe may have formed via similar
Understanding these processes may in turn fuel support for the idea of ancient oceans on Mars.
examination of THEMIS, MOLA, Viking, and Mariner data and images,
planetary scientists have found that areas on the northern plains of
Mars are divided into large polygon-shaped portions and that sets of
these polygons span extensive areas of the Martian surface. Smaller
polygon-shaped bodies are found elsewhere on Mars, but these are best
explained by thermal contraction processes similar to those in
terrestrial permafrost environments and not likely to form larger
the August 2012 issue of GSA Today, Lorena Moscardelli and her
colleagues from The University of Texas at Austin present a detailed
comparison of the geometric features of these large Martian polygons and
similar features found in deep-sea sediments here on Earth. Moscardelli
and colleagues note striking similarities.
Earth, polygon-shaped areas, with the edges formed by faults, are
common in fine-grained deep-sea sediments. Some of the best examples of
these polygon-fault areas are found in the North Sea and the Norwegian
Sea. These are imaged using detailed, 3D seismic surveys conducted to
search for offshore oil and gas deposits. Images reproduced in this
paper show that these deep-water polygons are also 1,000 meters or
greater in diameter.
the details of deep-sea polygon formation on Earth are complex,
Moscardelli and her colleagues conclude that the majority of these
polygons form in a common environment: sediments made up of fine-grained
clays in ocean basins that are deeper than 500 meters, and when these
sediments are only shallowly buried by younger sediments. A key
observation—also made recently by Michelle Cooke at the University of
Massachusetts—is that the physical mechanism of polygon formation
requires a thick, wet, and mechanically weak layer of sediment.
and colleagues also conclude that the slope angle of the sea floor
plays an important role in both the formation and preservation of these
polygons. Where the seafloor slope is very gentle (slopes less than half
a degree), the polygons have very regular shapes and sizes. In many
locations where polygons have formed on top of buried topographic
features on the seafloor, the shapes of the polygons were altered, and
in some cases were broken up and disrupted where the slopes were
steepest. Both observations are consistent with deformation of the soft
marine sediments as they creep or flow downslope in these areas.
the northern plains of Mars, where the surface is basically flat, the
polygons have very regular shapes and sizes—remarkably similar to the
deep-sea polygons found on Earth. In places where the topography on Mars
is more varied, and where there may be evidence for other
sediment-transport features on the surface, areas of deformed and
disrupted polygons can be found—again similar to the disrupted polygons
here on Earth.
the basis of these striking similarities, the University of Texas at
Austin team concludes that these features most likely share a common
origin and were formed by similar mechanisms in a similar environment.
The team argues that the Martian polygons were formed within a thick,
wet, and weak layer of fine-grained sediments that were deposited in a
deep-water setting, similar to the Earth polygons. Thus, these
interesting geometric features may provide additional evidence for the
existence of an ocean in the northern portion of Mars approximately
three billion years ago.
Source: Geological Society of America