This week’s image comes from Mars and shows one of the
canyons of Aram Chaos. This channel is one of many which riddle the landscape
of this region, creating an area of “chaos terrain”. The image I posted on Monday
is part of this HiRISE image, and credit goes to the NASA HiRISE team. A Themis
image of the whole basin, showing the jumble of blocks which make up the Chaos
terrain is shown below.
Aram Chaos is located where the eastern end of the Valles Marinaris
opens out into the Chryse planitia. This places it near the “dichotomy boundary”,
the line which separates the northern lowlands of Mars, from the heavily
cratered highlands of the southern hemisphere. This region of the planet is
very interesting, as it marks the dramatic shift from one terrain type to
another. It has been speculated that the northern lowlands were once a vast
sea, the dichotomy boundary certainly looks like an ancient shoreline. However
there is considerable debate as to whether a sea could have formed in the past.
It certainly seems likely that early Mars had substantially more liquid water
than it does today, but whether there were once oceans like those of Earth remains
uncertain. It is likely that smaller bodies of water occurred in a more ephemeral
manner, freezing as the climate shifted over time.
This brings us back to the Aram Chaos, which has been the
site of one of these bodies of water at several points during its history. The site
consists of a large impact crater 280 km in diameter. This crater has been
heavily modified by later processes, producing a distinctive region of chaotic
terrain. The basin is filled with large canyons which separate huge mesas,
blocks of stone kilometres to tens of kilometres across. It is the jumble of
blocks and mesas which gives areas of chaos terrain their name. In satellite images
of the surface they look like a complex labyrinth etched into the surface of
Mars. These blocks formed due to the thawing of water at this site. The sedimentary
materials here were gradually deposited over time, as an accumulation of water
saturated dust, sand and ultimately ice. It all froze into a solid mass,
filling the basin. However at a later point in the history of Mars there was a sudden
rise in temperature, probably due to the intrusion of magma into the ground
below these deposits. This caused massive melting and released the water which
had been frozen in the ground in the form of ice.
Much of this water overflowed the basin, carving an outflow channel
which extends away from Aram Chaos into the Ares Vallis. The formation of this
outflow channel wasn’t the only dramatic effect which this water had on the
landscape. Ice has a much larger volume than liquid water, so the thawing of
the ground ice led to massive amounts of collapse across the basin. This is
what led to the jumble of blocks and canyons that characterise the region. A bit
more erosion over the following millennia resulted in the characteristic
landscape of blocks and canyons seen today.
Studying the morphology and mineralogy of areas like Aram
Chaos can tell us a great deal about their history. We can infer the processes
which took place from the landscape, and the presence of sedimentary material
overlaying the chaos terrain indicates that it remained flooded for some time,
allowing material to accumulate. This fascinating area has been imaged by NASA and
ESA spacecraft many times and you can learn more about its history at the links
below.
In other news I’ve just had a paper published in the journal
Icarus. It is open access so if you would like to find out about the strange
boulder patterns of the martian northern plains then check it out. It’s
obviously a lot more detailed than the articles I’ve been writing here, but has
just as many cool HiRISE images! http://www.sciencedirect.com/science/article/pii/S0019103517301082
Further Reading:
Image Credits:
HiRISE image of chaos terrain: http://www.uahirise.org/ESP_011792_1795
The Aram Chaos Basin: https://themis.asu.edu/files/features/050_aram_chaos/050aramchaos.png
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