Zach Morse, Livio L. Tornabene, Radu Capitan and Eric Pilles wrote:Yardangs: Nature’s Weathervanes (ESP_050420_1910) (HiClip)
The prominent tear-shaped features in this image are erosional features called yardangs. Yardangs are composed of sand grains that have clumped together and have become more resistant to erosion than their surrounding materials.
As the winds of Mars blow and erode away at the landscape, the more cohesive rock is left behind as a standing feature. (This Context Camera image shows several examples of yardangs that overlie the darker iron-rich material that makes up the lava plains in the southern portion of Elysium Planitia.) Resistant as they may be, the yardangs are not permanent, and will eventually be eroded away by the persistence of the Martian winds.
For scientists observing the Red Planet, yardangs serve as a useful indicator of regional prevailing wind direction. The sandy structures are slowly eroded down and carved into elongated shapes that point in the downwind direction, like giant weathervanes. In this instance, the yardangs are all aligned, pointing towards north-northwest. This shows that the winds in this area generally gust in that direction.
Matthew Bourassa, Livio Tornabene, Eric Pilles, and Radu Capitan wrote:Honeycomb-Textured Landforms in Northwestern Hellas Planitia (ESP_052430_1425) (HiClip)
This image targets a portion of a group of honeycomb-textured landforms in northwestern Hellas Planitia, which is part of one of the largest and most ancient impact basins on Mars.
In a larger Context Camera image, the individual “cells” are about 5 to 10 kilometers wide. With HiRISE, we see much greater detail of these cells, like sand ripples that indicate wind erosion has played some role here. We also see distinctive exposures of bedrock that cut across the floor and wall of the cells. These resemble dykes, which are usually formed by volcanic activity.
Additionally, the lack of impact craters suggests that the landscape, along with these features, have been recently reshaped by a process, or number of processes that may even be active today. Scientists have been debating how these honeycombed features are created, theorizing from glacial events, lake formation, volcanic activity, and tectonic activity, to wind erosion.
Radu Capitan, Livio Tornabene, Eric Pilles and Matt Bourassa wrote:An Inverted Crater West of Mawrth Vallis (PSP_009115_2040) (HiClip)
This image captures details of an approximately 1-kilometer inverted crater west of Mawrth Vallis. A Context Camera image provides context for the erosional features observed at this site. The location of this HiRISE image is north of the proposed landing ellipse for the ExoMars 2020 rover mission that will investigate diverse rocks and minerals related to ancient water-related activity in this region.
Prolonged erosion removed less resistant rocks leaving behind other rocks that stand up locally such as the crater seen here and other nearby remnants. These resistant layers may belong to a phase of volcanism and/or water-related activity that carved Mawrth Vallis and filled in existing craters, and other lower-lying depressions, with darker materials.
Erosion has also exposed these layers down to older, more resistant lighter rocks that are clay-bearing. The diversity of exposed bedrock made this location an ideal candidate for exploring a potentially water-rich ancient environment that might have once harbored life.
HiRISE Science Team wrote:A Collapsed Crater Rim (ESP_049999_1450) (HiClip)
The eastern rim of this small 3.5-kilometer crater appears to have collapsed into a much larger crater (about 14-kilometers wide). The larger crater has a large ice flow around its central peak, and is non-circular, with large blocks further suggesting structural collapse of the terrain due to what are called periglacial processes.
Understanding the composition of this small crater may inform us of the ice content of the surrounding terrain.
Credit: NASA/JPL-Caltech/University of Arizona
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