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Planetary Geology

Unit Two
Introduction to Impact Cratering

Answer Key

1. a. The crater.
   b. Undisturbed surface layer of sand.
   c. No.
   d. Thick and continuous near the crater, thin and discontinuous far from the crater.
2. Not much, although the ejecta of the 65 degree impact may be slightly oblong.
   
   Part B
   
   

   	Velocity (m/sec)	Mass (kg)	KE (Nm = kg m2/sec2)	Crater Diameter (cm)
   Shot 1	1.4	~0.002	0.00196	~2
   Shot 2	6.3	~0.002	0.03969	~4
   Shot 3	14*	~0.002	0.196	~5
   Shot 4	69*	~0.002	4.761	~11

   
   * velocities are approximate; NM = Newton x meter
   
   Part C
   
   

   	Velocity (m/sec)	Mass (kg)	KE (Nm = kg m2/sec2)	Crater Diameter (cm)
   Shot 1 (4 mm)	6.3	~0.00034	0.0067473	~2.5
   Shot 2 (8 mm)	6.3	~0.002	0.03969	~3.5
   Shot 3 (18 mm)	6.3	~0.028	0.55566	~7
   Shot 4 (25 mm)	6.3	~0.067	1.329615	~7

   
   
   Part D
   
   

   	Velocity (m/sec)	Mass (kg)	KE (Nm = kg m2/sec2)	Crater Diameter (cm)
   Shot 1 (steel)	6.3	~0.028	0.55566	~7
   Shot 2 (glass)	6.3	~0.008	0.15876	~6
   Shot 3 (wood)	6.3	~0.002	0.03969	~3.5

   
   
3. As impact angle decreases toward 10 degree, ejecta becomes more oblong pointing downrange. Ejecta is absent on the uprange side of the crater.
4. a. Low angle.
   b. Entered from the east and bounced off the surface leaving two craters with an oblong ejecta pattern.
5. a. The higher the kinetic energy, the larger the crater.
   b. Higher velocities produce larger craters.
   c. Larger masses produce larger craters.
   d. Larger sizes (of the same density material) produce larger craters. Mass (density) is the controlling factor. Size (radius) is not a factor in the equation for kinetic energy. Instructor's note: Impacting objects in space have different densities. For example, meteorites occur as high density objects (iron meteorites) or as lower density objects (stony meteorites). Comets are composed mostly of water ice and have relatively low density. Like the foam ball, impacting comets might not form a crater at all.
   e. Velocity of the projectile is most important, as shown by the kinetic energy equation.
6. Craters are better preserved on flat terrain. In rugged areas, craters can be modified by landslides (mass wasting).

 

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