Using Boulder Diameter Crater Diameter Ratios to Differentiate
Using Boulder Diameter- Crater Diameter Ratios to Differentiate Primary from Secondary Craters on the Lunar Surface Cody Carroll, Ally Fess, and Hannah Adams Kickapoo High School April 1 st, 2011
Purpose of Research To distinguish primary craters from secondary craters on the lunar surface using qualitative and quantitative properties.
Study Area: Southeastern Mare Imbrium Lambert Euler Pytheas Between latitudes: 10°N-30°N and longitudes: 20°W-40°W
The Formation of Secondary Craters
Significance of Study Being able to differentiate between primary and secondary craters enables a more accurate method of relative dating of the lunar surface.
Secondary craters, due to the trajectory angles from the primary impact site, should demonstrate a more eccentric shape than primary craters. Secondary craters should have asymmetrical ejecta rays of varying length distributed unevenly around the crater rim. “Ballistics of the Copernican Ray System, ” E. M. Shoemaker
Secondary craters should demonstrate a larger ratio of boulder-diameter/ crater-diameter than primary craters. R= Bd/Cd Ruler set in scale of pixels Conversion factor of: . 513 m/pixel
Boulders of secondary craters should be chaotically distributed and oriented to the downrange region of the crater. M 137699035 LE
M 142421418 LE (lower) M 144857093 RE (bottom) Secondary M 144870473 LE (upper) Primary M 142394256 LE Secondary Primary
M 144856909 LE (lower) Secondary M 137699035 LE (upper) Secondary M 142421418 LE (upper) Primary M 144870473 LE (near center) Primary
Quantitative Data Primary Crater Results Image Number Diameter (m) Average Boulder Diameter (m) Ratio of Crater to Boulder M 142394256 LE 410 1. 846 0. 0045 M 142421418 LE (1) 651. 51 12. 302 0. 018 M 144856909 LE (2) 800 6. 4125 0. 008 M 144870473 LE (1) 461. 7 5. 8482 0. 01266 M 144870473 LE (3) 220. 59 3. 8475 0. 01744 M 144857093 RE 605. 34 5. 8995 0. 009745
Quantitative Data Secondary Crater Results Image Number Diameter (m) Average Boulder Diameter (m) Ratio of Crater to Boulder M 137699035 LE (1) 117. 99 2. 975 0. 0252 M 137699035 LE (2) 292. 41 6. 158 0. 0215 M 142421418 LE (2) 123. 12 3. 249 0. 0302 M 144856909 LE (1) 548. 91 39. 501 0. 0719 M 144856909 LE (2) 513 10. 26 0. 02 M 144870473 LE (2) 143 4. 8936 0. 03 M 144857093 LE (1) 107. 73 2. 949 0. 027 M 144857093 RE 104. 652 5. 892 0. 0558
Analysis of Primary Craters (Diameter, Avg. Boulder size, Bd/Cd ratios)
Analysis of Secondary Craters (Diameter, Avg. Boulder size, Bd/Cd ratios)
Comparison of Primary to Secondary Boulder -diameter/ Crater-diameter Ratios *Proximal crater Distant Secondary Crater- Bd/Cd ratio Primary Crater- Bd/Cd ratio
Differentiating Ejecta Materials M 144856909 LE
Conclusions • Secondary craters, due to the trajectory angles from the primary impact site, did demonstrate a more eccentric shape than primary craters. • No correlation was observed between secondary craters and asymmetrical ejecta rays of varying length distributed unevenly around the crater rim. • Secondary craters did demonstrate a larger ratio (. 02 and above) of boulder-size/ crater-size than primary craters. • Boulders of secondary craters were unevenly distributed and oriented to the downrange region of the crater (within the crater rim or within 60 m outside of downrange rim).
References • Bart, Gwendolyn D. and Melosh, H. J. (2007). Using Lunar Boulders to distinguish primary from distant secondary craters. Geophysical Research Letters, Volume 34, L 07203. pgs. 1 -5 • Shoemaker, E. M. (1960). Ballistics of the Copernican Ray System. Proceedings of Lunar and Planetary Exploratorium Colloquim, Volume 2 Number 2, pgs. 7 -20. • Mc. Ewen, Alfred S. , Preblich, Brandon S. , Turtle, Elizabeth P. , Artemieva, Natalia A. and many others. (2005). The rayed crater Zunil and interpretations of small impact craters on Mars. Retrieved from http: //www. sciencedirect. com
Acknowledgements • Mr. Andrew Shaner – For his providing of Adobe Photoshop for crater/ lunar boulder analysis • Dr. Georgiana Kramer – for her student mentoring on scientific analysis and conversion of pixel size to distance on imagery • Mr. Lynn Coffey – For his assistance in formatting of graphical analysis of data
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