More Martian pits, filled and unfilled!
Time for what has almost become a monthly pit report from Mars Reconnaissance Orbiter (MRO). The November image download from the spacecraft’s high resolution camera included two pit-related photographs, both very different. To the right is the first, cropped to focus on the pit and the immediate surrounding terrain. Below that is a wider overview map to provide the context.
This pit’s location is indicated by the white box at the southern end of a region dubbed Ceraunius Fossae, made of hundreds and hundreds of parallel north-south fissures extending more than seven hundred miles south of the giant volcano Alba Mons and caused when the ground was stretched from below, causing it to crack.
This surrounding terrain helps to explain the pit’s origin. First it is located in a north-south depression with a number of other less pronounced depressions. While these do not line up precisely, they still suggest that they are sinkholes where the surface material is draining downward into voids below. Normally the assumption would be the existence of a lava tube, but here the downward grade is very small. Instead, what is likely happening is that the ground is being stretched, causing cracks to form into which surface material slips downward.
The Ceraunius Fossae fractures are extensional features produced when the crust is stretched apart…. Mechanical studies indicate that a regional pattern of radiating graben and rifts is consistent with stresses caused by loading of the lithosphere by the enormous weight of the Tharsis bulge….Several generations of grabens with slightly different orientations are present in Ceraunius Fossae, indicating that stress fields have changed somewhat over time.
In addition to producing normal faults and graben, extensional stresses can produce dilatant fractures or tension cracks that can open up subsurface voids. When surface material slides into the void, a pit crater may form. Pit craters are distinguishable from impact craters in lacking raised rims and surrounding ejecta blankets. On Mars, individual pit craters can coalesce to form crater chains (catenae) or troughs with scalloped edges.
That’s what we see here. The pit is suggestive of a void below, but it is likely not going to be a long coherent underground passage but a serious of random gaps, aligned roughly along the larger crack and producing the various depressions on the surface.
Today’s second pit is of an entire different nature.
» Read more
Time for what has almost become a monthly pit report from Mars Reconnaissance Orbiter (MRO). The November image download from the spacecraft’s high resolution camera included two pit-related photographs, both very different. To the right is the first, cropped to focus on the pit and the immediate surrounding terrain. Below that is a wider overview map to provide the context.
This pit’s location is indicated by the white box at the southern end of a region dubbed Ceraunius Fossae, made of hundreds and hundreds of parallel north-south fissures extending more than seven hundred miles south of the giant volcano Alba Mons and caused when the ground was stretched from below, causing it to crack.
This surrounding terrain helps to explain the pit’s origin. First it is located in a north-south depression with a number of other less pronounced depressions. While these do not line up precisely, they still suggest that they are sinkholes where the surface material is draining downward into voids below. Normally the assumption would be the existence of a lava tube, but here the downward grade is very small. Instead, what is likely happening is that the ground is being stretched, causing cracks to form into which surface material slips downward.
The Ceraunius Fossae fractures are extensional features produced when the crust is stretched apart…. Mechanical studies indicate that a regional pattern of radiating graben and rifts is consistent with stresses caused by loading of the lithosphere by the enormous weight of the Tharsis bulge….Several generations of grabens with slightly different orientations are present in Ceraunius Fossae, indicating that stress fields have changed somewhat over time.
In addition to producing normal faults and graben, extensional stresses can produce dilatant fractures or tension cracks that can open up subsurface voids. When surface material slides into the void, a pit crater may form. Pit craters are distinguishable from impact craters in lacking raised rims and surrounding ejecta blankets. On Mars, individual pit craters can coalesce to form crater chains (catenae) or troughs with scalloped edges.
That’s what we see here. The pit is suggestive of a void below, but it is likely not going to be a long coherent underground passage but a serious of random gaps, aligned roughly along the larger crack and producing the various depressions on the surface.
Today’s second pit is of an entire different nature.
» Read more