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| My lovely code. I wrote nested if statements in two different ways, though, and I'm not sure how I feel about that. |
First, I sorted it by crater ID (because every crater has it's own unique ID number). Then I created a set of ranges for the latitudes (because 18.100 degrees and 18.105 degrees really aren't that different when we're dealing with 180 degrees overall). Each range includes 10 degrees. I also had it do a similar set of ranges for the crater depth. Morphology was different - it's categorical data - but I was only interested in the first structure, so I put some code in to do that. After all of that rearranging, I had the program make frequency distributions for all of the variables I'm interested in (see my Mars Missions post for the entire backstory).
Let's look at each frequency distribution separately. First up, latitude.
| Crater Latitude (degrees) | ||||
|---|---|---|---|---|
| lat_range | Frequency | Percent | Cumulative Frequency | Cumulative Percent |
| 01. (-90,-80] | 631 | 0.16 | 631 | 0.16 |
| 02. (-80,-70] | 6984 | 1.82 | 7615 | 1.98 |
| 03. (-70,-60] | 13527 | 3.52 | 21142 | 5.50 |
| 04. (-60,-50] | 18758 | 4.88 | 39900 | 10.38 |
| 05. (-50,-40] | 25396 | 6.61 | 65296 | 16.99 |
| 06. (-40,-30] | 34577 | 9.00 | 99873 | 25.99 |
| 07. (-30,-20] | 46504 | 12.10 | 146377 | 38.08 |
| 08. (-20,-10] | 46158 | 12.01 | 192535 | 50.09 |
| 09. (-10,0] | 40921 | 10.65 | 233456 | 60.74 |
| 10. (0,10] | 32362 | 8.42 | 265818 | 69.16 |
| 11. (10,20] | 30411 | 7.91 | 296229 | 77.07 |
| 12. (20,30] | 28990 | 7.54 | 325219 | 84.62 |
| 13. (30,40] | 23365 | 6.08 | 348584 | 90.70 |
| 14. (40,50] | 14160 | 3.68 | 362744 | 94.38 |
| 15. (50,60] | 10801 | 2.81 | 373545 | 97.19 |
| 16. (60,70] | 7974 | 2.07 | 381519 | 99.27 |
| 17. (70,80] | 2780 | 0.72 | 384299 | 99.99 |
| 18. (80,90] | 44 | 0.01 | 384343 | 100.00 |
This table counts how many craters can be found in each latitude. From the table, we can see that there are significantly more craters in the -50 to 30 degree ranges (74.24%) than there are as we get closer to the poles. In other words, just 44% of the latitude contains 74% of the craters. In fact, 24.11% of craters fall within only 20 degrees of latitude (between -30 and -10 degrees), just south of the equator. However, we should keep in mind that the latitudes closer to the equator also have more land area than the ones closer to the poles (and more area = more places for craters to exist).
Next we have the number of layers:
| Number of Layers | ||||
|---|---|---|---|---|
| NUMBER_LAYERS | Frequency | Percent | Cumulative Frequency | Cumulative Percent |
| 0 | 364612 | 94.87 | 364612 | 94.87 |
| 1 | 15467 | 4.02 | 380079 | 98.89 |
| 2 | 3435 | 0.89 | 383514 | 99.78 |
| 3 | 739 | 0.19 | 384253 | 99.98 |
| 4 | 85 | 0.02 | 384338 | 100.00 |
| 5 | 5 | 0.00 | 384343 | 100.00 |
| Crater Depth (km) | ||||
|---|---|---|---|---|
| depth | Frequency | Percent | Cumulative Frequency | Cumulative Percent |
| [-0.5,0) | 10 | 0.00 | 10 | 0.00 |
| [0,0.5) | 363592 | 94.60 | 363602 | 94.60 |
| [0.5,1) | 15803 | 4.11 | 379405 | 98.72 |
| [1,1.5) | 3567 | 0.93 | 382972 | 99.64 |
| [1.5,2) | 1039 | 0.27 | 384011 | 99.91 |
| [2,2.5) | 265 | 0.07 | 384276 | 99.98 |
| [2.5,3) | 51 | 0.01 | 384327 | 100.00 |
| [3,3.5) | 9 | 0.00 | 384336 | 100.00 |
| [3.5,4) | 3 | 0.00 | 384339 | 100.00 |
| [4,4.5) | 1 | 0.00 | 384340 | 100.00 |
| [4.5,5) | 3 | 0.00 | 384343 | 100.00 |
The crater depths are grouped into ranges of 0.5 km. Negative numbers indicate that the crater actually rises about the surrounding ground (and I'll talk about that more after the next table). The thing that stands out is that most craters (94.6%) have depths between 0 and 0.5 km. (I also want to point out that I used interval notation to describe the ranges so [0,0.5) includes craters that have a depth of 0 km but not craters that have a depth of 0.5 km. And obviously it includes everything in between 0 and 0.5 km.) And 98.72% of the craters are less than 1 km deep. The deepest craters in this dataset are nearing 5km (3 miles!) deep but there are only 3 of them (out of about 300,000 craters).
And finally, we have the morphology table:
| Morphology of Innermost Ejecta | ||||
|---|---|---|---|---|
| morph | Frequency | Percent | Cumulative Frequency | Cumulative Percent |
| Frequency Missing = 339718 | ||||
| DLE | 2777 | 6.22 | 2777 | 6.22 |
| MLE | 581 | 1.30 | 3358 | 7.52 |
| Pd | 2 | 0.00 | 3360 | 7.53 |
| Rd | 27069 | 60.66 | 30429 | 68.19 |
| SLE | 14196 | 31.81 | 44625 | 100.00 |
Craters can have a lot of different shapes and structures and so scientists use codes (instead of words) to describe them. For my data, I looked at the primary structure of the innermost ejecta (in other words, I only looked at the first code for each crater). Because these codes and terms are probably unfamiliar (they were to me, anyway), I've got another post just about morphology that gives descriptions and pictures for each type.
But, here's the TL;DR:
SLE = Single-Layer ejecta
DLE = Double-layer ejecta
MLE = Multiple-layer ejecta
Pd= Pedestal
Rd=Radial
Getting back to the morphology table, we can see that most craters that have been classified are of the radial type (60.66%), followed by single-layer ejecta (31.81%). There are not many pedestal craters, although it should be noted that this data table only looks at the primary morphology and pedestal craters may also be listed at SLEPd (single-layer ejecta, pedestal type) where the ejecta closest to the center of the crater is of the SLE type and then, moving farther out, it becomes a pedestal type. I should also point out that most of the craters (88%) are actually missing a description of their morphology.
And that's it for now. In my next post, I'll make some graphs to give a clearer picture of the data.
