some notes for the age calculation

The first set calculated for all craters (for a good comparison starting point) used a Melosh Hard Rock scaling law with target density=2.8 and projectile density=2.6. 

Note that the Melosh scaling law is for gravity regime only. Simone and I discussed this and determined that much previous work used this law, so this makes our work more comparible. Plus uncertain where transition to strength regime is (and can vary for different terrains).

Also used NEO population and uniform target.

We find a majority of the data are fit well by this. We are currently exploring poor fits to determine if it is geology or if the scaling law needs to be adjusted.

Different possible scaling laws are shown in the figure "moon_craterSL_formichelle.png"

Note that we have calculated ages for SFDs with both OS not included and included (designated by *_sec in filename). In general, find that the ages are not greatly effected, but there are a few cases (mostly younger craters) where it can make a large difference. Also note in Simone's plots of the SFDs with OSs the fit without OSs is shown in orange, while the current fit is white.

Trying to improve poor fits:
icarus, mclaughlin, laue: the new fits are forced to pass through small D. (noted by "2" added to file name)

albiruni: the old fit was good.

paracelsus, vlacq, neumayer: new fit using H&H hard rock with a
strength of Y=2e7. all other parameters are the same. (noted by "HH" added to file name)

Note the transition from gravity to strength shifts to larger diameters as the target becomes stronger. Therefore, the fact that we see the transition for a few craters mean these have a "harder" surface than the majority of craters that we don't see the transition. However, we don't know where the transition is for these majority that we don't see - it could be at 500 m, just below our limit. Furthermore, these strength changes (even a couple of order of magnitudes) are minor and do not suggest significant changes in material. This is good because of the variety of geologies we observe for the crater floors.

millikan, tikhov, shayn, mezentsev: neither strength scaling law nor
layering work fine. I attach a couople of examples to show that
the fit does not improve.

rosemberger: good fit achieved with layering. thickness H=0.26km.
all other parameters are the same.
the top layer has Y=2e7, the bottom layer has Y=2e8

joule: good fit achieved with layering. thickness H=0.20km.
all other parameters are the same.
the top layer has Y=2e7, the bottom layer has Y=2e8

freundlich: good fit achieved with layering. thickness H=0.33km.
all other parameters are the same.
the top layer has Y=2e7, the bottom layer has Y=2e8

(noted by "layer" added to file name)

Simone and I note that having a constant density with depth and a relatively minor change in strength may be consistent with the small craters sizes (~ 1km) being effected, which likely only excavate a few hundred meters.

Last edited by MRK 5/14/2012.