This blog covers the Data Management and Visualization course taught by Wesleyan University via Coursera online learning platform.
The first assignment is about developing a research question. Five codebooks and data sets were provided on different subject areas.
The instruction is to choose one data set, select main topic of interest, prepare a codebook with variables that measure the selected topic of interest, develop research questions, identify a possible second topic of interest, perform a literature review and finally formulate a hypothesis.
Chosen Data Set:
I will be studying the Mars Crater codebook.
This study is not a detailed scientific or academic research on Mars. The primary objective of this exercise is to develop research question and hypothesis formulation skills.
For the purpose of this exercise, a new global database for Mars (Mars Crater codebook) was provided. It contains extensive information about the properties of 384, 343 craters. These properties include crater location, crater diameter, crater depth, number of ejecta layers and crater morphology.
Mars, like other planets in the solar system, underwent a period of heavy bombardment from asteroids travelling at high velocity. A large hole or depression is formed on the surface of Mars upon impact. This is known as impact cratering. These craters are of different sizes, depth and morphology. Upon impact, materials are thrown out and deposited around the craters. These materials are called ejecta. Satellite images suggest that different regions of Mars have different number of impact craters.
Main Topic of Interest and Research Questions:
My main topic of interest is about patterns of crater distribution on the surface of Mars. To explore this topic further, I'll consider the following questions;
- How does the number of craters vary on different regions of Mars?
- Do craters occur most often near the equator, the southern or northern hemisphere?
- Is crater diameter associated with crater depth?
- Is there a correlation between crater depth and the number of layers around the craters?
- Does crater depth depend on crater location?
- Does crater diameter vary with location in a well-defined pattern?
To answer these research questions, I'll examine the details of 384, 343 craters in the Martian database created by Stuart Robbins at the University of Colorado. Several Mars crater variables will be used in this analysis.
The variables associated with spatial location are;
- LATITUDE_CIRCLE_IMAGE – latitude from the derived center of a non-‐linear least-‐squares circle fit to the vertices selected to manually identify the crater rim (units are decimal degrees North)
- LONGITUDE_CIRCLE_IMAGE – longitude from the derived center of a non-‐linear least-‐squares circle fit to the vertices selected to manually identify the crater rim (units are decimal degrees East)
Variables associated with crater dimension – diameter, depth and number of layers:
- DIAM_CIRCLE_IMAGE – diameter from a non-‐linear least squares circle fit to the vertices selected to manually identify the crater rim (units are km)
- DEPTH_RIMFLOOR_TOPOG – average elevation of each of the manually determined N points along (or inside) the crater rim(units are km)
- NUMBER_LAYERS – the maximum number of cohesive layers in any azimuthal direction that could be reliably identified.
Second Topic of Interest:
The second topic to consider will be about crater morphology. The following questions will be examined;
- Does morphology of impact craters change with crater diameter?
- Is crater morphology associated with crater depth-to-diameter ratio?
Second Set of Variables:
Additional variables will be required to further investigate the second topic. These include;
- MORPHOLOGY_EJECTA_1 – ejecta morphology classified. Examples below.
If there are multiple values, separated by a “/”, then the order is the inner-‐most ejecta through the outer-‐most, or the top-‐most through the bottom-‐most
- MORPHOLOGY_EJECTA_2 – the morphology of the layer(s) itself/themselves. This classification system is unique to this work.
- MORPHOLOGY_EJECTA_3 – overall texture and/pr shape of some of the layer(s)/ejecta that are generally unique and deserve separate morphological classification.
Detailed research has been done on impact craters on the surface of Mars. Previous works particularly targeted the relationships between depth and diameter of various craters at different locations on Mars. Most of these studies have also revealed the origins of the craters and crater associated morphologies caused by meteoritic impacts which might have happened randomly or in a particular order.
Proper study of Martian impact craters has been challenging in the past due to lack of robust record of Mars craters alongside reliable measurements. However, Stuart Robbins in his classic PhD research (2011) largely resolved this problem by developing modern global database of 384, 343 Mars impact craters. This database contains accurate description of crater location and dimensions, including crater diameter, depth and ejecta morphology. Stuart isolated these craters into primary and secondary clusters, which he used to age-date the volcanic calderas on planet Mars. However, it will be good to further investigate if there are definitive trends in crater sizes and morphology within these individual crater clusters.
Nadine Barlow used new data from Mars Global Surveyor (MGS) and Mars Odyssey missions to obtain new insight into the morphology of Mars craters. The research concluded that multiple-layer ejecta (MLE), based on identifiable number of layers exceeding 2 layers, are located mainly within the lower to middle latitude regions. This morphology was observed to be associated with craters within the 15 to 60km diameter range. (Barlow and Perez 2003; Barlow, 2006)
Although, a clear crater morphology trend has been identified by Nadine for specific locations on Mars, it will still be important to verify whether such morphology trends exist in other regions of Mars. Additionally, further analysis may be required to verify if good correlation exists between ejecta morphology and other crater variables apart from crater diameter.
The above literature review was conducted mainly by online Mars Crater research in Google Scholar and by reading the PhD thesis of Stuart Robbins provided in the codebook.
I have formulated 2 hypotheses based on my research questions and literature review. My hypotheses have been written in a more traditional scientific format.
- If craters were formed by non-random meteoritic impacts, then there will be well defined relationships between crater diameter, depth and location.
- If crater morphology depends on the nature of the impactor, then crater morphology will be associated with crater diameter-to-depth ratios.
References for Literature Review:
Barlow, Nadine. "Impact craters in the northern hemisphere of Mars: Layer ejecta and central pit characteristics".Meteoritics & Planetary Science 41, Nr 10, (2006): 1425–1436.
Barlow N. G. and Perez C. B. 2003. Martian impact crater ejecta morphologies as indicators of the distribution of subsurface volatiles. Journal of Geophysical Research, doi:10.1029/2002JE002036.
Robbins, Stuart. "Planetary Surface Properties, Cratering Physics, and the Volcanic History of Mars from a New Global Martian Crater Database." PhD Thesis, University of Colorado (2011): 251 pages.
Posted on November 29, 2015 by Okechukwu Ossai