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Figure 1 of this article about craters and collapse features on Mars with high depth/diameter ratios shows that ratios higher than 0.2 are exceptional.

This presentation of the Program of the Second MSL Landing Site Workshop about possible landing sites in Sinus Meridiani shows an image of a "crater" that is 2.4 km wide and 750 meters deep !

Collapse feature

Because the ratio of this feature is more than 0.3 and it has no clear rim, it is very likely that this is not an impact crater at all.

Are there more known features on Mars with such a very high depth/diameter ratio ?

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  • $\begingroup$ Does this feature in the image have a name? $\endgroup$ – BlueCoder Sep 12 '18 at 11:44
  • $\begingroup$ @BlueCoder Could not find a name at planetarynames.wr.usgs.gov/nomenclature/AdvancedSearch so i think you could propose a name. $\endgroup$ – Cornelis in space Sep 12 '18 at 13:14
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    $\begingroup$ The concept of a depth to diameter ratio is an interesting idea. I'm still trying to get my head around it. In a way it's an analogous of the average/overall slope angle of the wall of the "crater". This angle will largely be dictated by the properties of the wall rock (ie, by way of example, loose sand will have a shallow angle, very competent basalt will have a high angle). Generally this angle will be the angle of rest for the rock type. The other things that will affect the depth of an impact crater will be the hardness & competency of of the host rock. $\endgroup$ – Fred Sep 12 '18 at 17:17
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    $\begingroup$ Taking some rough measurements from the screen. I get a diameter of 110 mm & a wall width of 30 mm (on the rightmost side). With a depth to diameter ratio of 0.3 the depth is 33 mm (0.3 x 110). Get the arc tan of (33/30) gives a wall angle of 47 degrees. $\endgroup$ – Fred Sep 12 '18 at 17:20
  • $\begingroup$ @Fred Thank you for your comments. Maybe we will find a similar, much smaller feature and then we could place a transparent dome on it to keep it warm.:) (I should have added "at Fred" to my earlier comment on Sept. 12) $\endgroup$ – Cornelis in space Sep 24 '18 at 8:09
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The d/D ratio of Martian craters vary from 0.1 to 0.4 with mean value of 0.23. The largest crater with diameter 33m has d/D ratio of 0.2 but smaller craters have higher d/D value. One crater has a surprisingly high d/D value: 0.5. A plot of d/D ratio vs diameter is drawn showing the variation in the values:

enter image description here

Shallower craters have d/D values of more than 0.3

enter image description here

a: 0.50 ; b: 0.42 ; c: 0.39 ; c: 0.42

The variation in this value depends on target material properties like varying strength, porosity, or layering of targets; or impactor conditions such as impact velocity, impact angle, or physical state of the bolide (i.e., strength, fractured versus cohesive). The dependencies are listed below:

  1. Spallation can be seen in targets with porosity up to 60%. The ratio of spall diameter to pit diameter is not strongly dependent on porosity and is between 1.5 and 3. The range of the ratio is similar to those found for microcraters on lunar rocks and glass targets in the laboratory.
  2. The depth of a crater cavity is a function of the density ratio of the projectile and target. However, it is also dependent on the impact velocity and porosity of the target.
  3. The normalized diameters of craters on porous targets tends to decrease with increasing target porosity. An empirical scaling law derived for porous sedimentary rocks based on conventional scaling laws is shown to be a reference for craters on brittle targets, including porous targets of various porosities.
  4. The depth-to-diameter ratio of the crater cavity is roughly 0.5 for tuff and gypsum, with porosities of about 43% and 50%, respectively. On the other hand, the ratio is about 0.2 for sandstones and cement mortar, although the porosity of cement mortar is about 40% and similar to that of tuff. No strong velocity dependence is evident in the depth-to-diameter ratio, although the ratio changes with impact velocity for microcraters produced on non-porous glass.
  5. Crater shape is roughly a trigonal pyramid for craters with a depth-to-diameter ratio of less than 0.3

References:

  1. Daubar, I. J., C. Atwood-Stone, S. Byrne, A. S. McEwen, and P. S. Russell (2014), The morphology of small fresh craters on Mars and the Moon, J. Geophys. Res. Planets, 119, 2620–2639, doi:10.1002/2014JE004671.
  2. Impact cratering on porous targets in the strength regime by Akiko M. Nakamura (PDF)
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