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:
Shallower craters have d/D values of more than 0.3
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:
- 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.
- 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 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.
- 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.
- Crater shape is roughly a trigonal pyramid for craters with a depth-to-diameter
ratio of less than 0.3
- 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.
- Impact cratering on porous targets in the strength regime by Akiko M. Nakamura (PDF)