HIRISE Science Team wrote:Layers in Flammarion Crater (ESP_027059_2055)
The objective of this observation is to examine layers. In and around this region, there are outcrops of layered terrain.
A high resolution image can see minute details that will enable us to start to catalog different types of layers and to discover under what conditions they are produced. In this particular image there is a cap rock on top of some poorly formed layers and some well formed layers.
This caption is based on the original science rationale.
Shane Byrne wrote:Nested Craters (ESP_027610_2205)
Impact craters that are only a few kilometers in size on Mars usually have simple bowl shaped interiors with craters in weaker material being larger than craters in stronger material.
Occasionally though, nature is more complicated and these simple rules don't apply. One such case is shown here where is appears as if there are craters nested within each other. These nested craters are probably caused by changes in the strength of the target material. This usually happens when a weaker material overlies a stronger material.
We can use craters like this to tell us something about what lies below the surface. What could be causing the change in strength in the subsurface? Mars has a lot of ice in its terrain near the surface. This ice-rich layer could be the weaker material and the deeper ice-free layer could be the stronger material.
Colin Dundas wrote:A Crater North of Coprates Chasma (ESP_027775_1675)
This image shows a fresh impact crater about 2 kilometer (1.2 miles) across. How do we know it is fresh?
The crater walls are steep and rocky, and fine striated texture is still visible on the ejecta. Over time, erosion and dust settling out of the atmosphere will smooth out such details. However, these processes are slow on Mars, and the crater is probably at least several million years old.
Craters like this are important targets for HiRISE for several reasons. The details of the fresh crater are interesting in themselves for studying impact processes, but crater walls can also provide great exposures of bedrock. The steep slopes are also good places to look for active processes like rockfalls happening today, especially when we can compare a series of images taken over several years.
Paul Geissler wrote:Dunes on the Move (ESP_027864_2295)
HiRISE has been carrying out a dedicated survey of sand dunes on Mars, determining whether and how fast the dunes move by observing repeatedly at intervals of Martian years. More than 60 sites have been monitored so far, showing that sand dunes from the equator to the poles are advancing at rates of up to 1 meter per Martian year.
These observations are still spotty, however, and tend to be concentrated in the tropics and the North Polar erg (the sand sea that surrounds the North Pole). One latitude band that had not been sampled at all lies between 30 and 65 degrees north. This observation is among a set of images acquired to fill that gap.
This image shows a variety of different dune types in southern Lyot Crater in the Northern lowlands at 48.9 degrees north. Transverse dunes to the west grade into longitudinal dunes downwind to the east and barchans to the south, possibly because of local winds channeled by topography in the impact basin. This image was intended to match the approximate illumination and viewing conditions of an earlier HiRISE observation that was made two Martian years earlier, in August 2008.
Detailed comparison of the two images shows movement on many of the dunes during this interval of nearly four Earth years. The subimage is an animation showing changes on one of the small barchans in the south of the dune field. The area pictured in the subimage is about 100 meters across. Winds from the west (left) have shifted the small ripples up the back of the dune towards the east. Sand has blown over the crest of the dune, cascaded down the steep slip face, and accumulated along the base of the slip face in the lee of the dune. In this way, the small dune advances slowly downwind.
Other images also show dune activity in this latitude band, adding to a growing suspicion that dunes are on the move everywhere on Mars, faster in some places than others.
Credit: NASA/JPL/University of Arizona
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