Lecture 20: Impact Tour

Question 1

distinctive features of impact craters

Answer 1

• circular
• steep sided and closed
• rim rocks are tilted away from the crater
• shattered rocks on the crater floor
• large angular blocks of rock scattered around crater
• presence of meteorite fragments
• sock minerals (indicative of extreme T and pressure)
• shatter cones
• melted rock due to impact

Question 2

shatter cones

Answer 2

• a conical fragment of host rock fractured by the shock wave generated by the impact
• striations radiation from the apes
• terrestrial rock

Question 3

gravity varies by very small amounts at different locations on the surface of the earth due to

Answer 3

• ellipsoid shape of the planet
• earth’s rotation
• irregular topography
• heterogeneities in the subsurface

Question 4

gravity signature of impact crater

Answer 4

• high gravity values: region denser than the surrounding material
• low gravity values: region less dense than the surrounding material
• impact craters usually correspond to low gravity anomalies

Question 5

crater counting

Answer 5

• in the absence of radiometric data, the surface of space bodies is dated using crater counting
• method has been calibrated with lunar data for which radiometric data is available
• ## knowing the cratering rate (# crater of a given size per unit time) the age can be estimated