Starship Asterisk*

Matthew Chojnacki wrote:

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Northwest Ius Chasma Landslide and Dune Field (ESP_026444_1720) (HiClip)

Landslides in Valles Marineris are truly enormous, sometimes stretching from one wall to the base of another. This 45-kilometer-long HiRISE image alone drops nearly 2 kilometers in elevation into Ius Chasma. This landslide, known as Ius Labes, would occupy the surface area of Delaware.

Here, we can see dark-toned material emanating from the landslide scarp and forming dunes and dark streaks that were carried downslope by the wind. Geologic context and compositional information from CRISM suggest this dune field was locally derived from landslide material. Other locations in this image show smaller ripples and smooth, rounded textures of the landslide, both attesting to long-lived wind transport and erosion.

This site records a long and complex geologic history of landscape evolution. This history likely includes: (1) ancient lava flows and ash fall deposits which were deposited horizontally and would eventually make what now is canyon wall material; (2) extensional forces rifted or faulted Valles Marineris; (3) mass wasting ensued where gravity forced weak and dislodged rock down into the canyon as massive landslides or smaller fans of boulders; (4) wind driven aeolian forces took small sand-sized particles to form dunes and ripples observable in this image, while also slowly eroding the landscape and modifying its shape.

Colin Dundas wrote:

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Knob in the South Polar Layered Deposits of Mars (ESP_032020_0955) (HiClip)

The South Polar Layered Deposits of Mars are a thick stack of layers of ice and dust, deposited over millions of years. The rate of deposition changes over time, and in some times and places the stack is eroded.

Here, a low mesa or ring of hills occurs near the edge of the layered deposits. It is likely that this feature was once an impact crater. The floor of the crater became resistant, and was left behind as the rest of the surface eroded.

Images like this one can show us where the layered deposits are being eroded, and how much ice and dust has been lost. This, in turn, helps us understand the history recorded in the layers.

This is a stereo pair with ESP_023066_0955.

Mike Mellon wrote:

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Mawrth Vallis Geodiversity (ESP_032125_2025) (HiClip)

This image shows a small portion of Mawrth Vallis, one of the many outflow channels feeding north into the Chryse Basin. This ancient valley once hosted flowing water. The erosive power of the flowing water rapidly cut down into the underlying layers of rock to expose a host of diverse geologic landforms visible today.

A focus of geologic study (at this site on Mars as well as many locations on Earth) is deciphering the juxtaposition of various rock structures and landforms. The superposition of one landform or strata above another, fractures and faults that disrupt one layer but not another, and the depths of certain mineralogical signatures all tell a story of the geological and climatological history of the region.

Intensely fractured bedrock is visible at all scales (meters to kilometers), revealing that subsurface rock has undergone a complex history of stresses and deformation, such as stretching, compression, and twisting. Wider dark ridges are also visible, crossing long distances through the fractured bedrock and between the various exposed layers. These ridges may be what geologists call "dikes," near vertical fissures in the subsurface rock that became injected with magma, and which later cooled into the is now an exposed vein of dark volcanic rock.

These dikes may be related to areas of dark and rough (likely volcanic) cap rock that now covers and protects the light toned strata below. Erosion through and around this cap rock has exposed a myriad of light toned layers. These layers reveal a past ancient environment where geologic material (perhaps volcanic ash, fine sand, and dust) settled slowly from the air or at the bottom of a standing body of water. In addition, spectroscopic signatures of phyllosilicate minerals (clays) indicates a history of geochemical alteration of primary minerals which in some way involved liquid water.

These geologic structures and the processes that formed them mostly predate the already ancient flood waters that carved Mawrth Vallis. However, processes continue to change and evolve the landscape into the present day. Overlying the surface are scattered dark dunes and small sand sheets. These landforms tells us that wind continues to move and shift the dark volcanic sands across the surface. In addition, lighter-toned loose soil and coatings of the ever present reddish dust (very fine grained weathered rock particles that is continuously blown around the planet) blankets much of the surface. The presence of this soil tell us that, while slow, rock continues to weather both physically and chemically, and break down into the finer soil particles.

Cathy Weitz wrote:

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Sediments in Ladon Basin (ESP_032297_1595) (HiClip)

This image shows light-toned layered deposits at the contact between the Ladon Valles channel and Ladon Basin.

These deposits could either be fluvial sediments transported along Ladon Valles when water carved out this channel, or they could be sediments deposited in Ladon Basin, perhaps when a lake existed here. Some of these light-toned deposits have mineral signatures consistent with clays, indicating favorable water conditions for life.