Astronomy quiz question: Venus versus Earth's moon

Astronomy 210 Quiz 7, Fall Semester 2010
Cuesta College, San Luis Obispo, CA

The small number of impact craters on Venus, compared to Earth's moon, is evidence of Venus':
(A) past oceans.
(B) lack of shield volcanoes.
(C) lack of tidal heating.
(D) younger surface.

Correct answer: (D)

The surfaces of all terrestrial planets (and Earth's moon) accumulated impact craters during the heavy bombardment phase of planetary formation. Geological activity is responsible for removing these impact craters (filling in with lava, folding down into the mantle from tectonic plate motion), such that a lack of impact craters corresponds to a greater amount of geological activity, and a newer (more recently solidified) surface.

Section 70160
(A) : 14 students
(B) : 3 students
(C) : 1 student
(D) : 21 students

"Success level": 58% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.39