Impact Crater Studies

What is the evidence? Crater counts—the number and distribution of impact craters on planetary surfaces; analysis of the size and shape of the craters (e. g., depth-to-diameter ratios, slope of crater walls); high-resolution photographs of impact craters; physical samples of materials from or near craters

What does it tell us? Crater counts provide information about the relative age of a planetary surface, the planet’s bombardment history, and erosion rates. Comparisons of crater size and shape tell us about the characteristics of the materials on the planet’s surface. Radiometric dating of crater samples provides their absolute ages.

Key limitations: Craters on some planetary surfaces, such as Earth and Mars, have been altered by erosion and other processes; smaller craters are more susceptible to change; newer craters may obscure older craters; assumptions are required about the rate of impacts over time; resolution of images is limited

Example: Counting Craters

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Crater counts and elevation data from the Lunar Reconnaissance Orbiter (LRO) generate detailed maps of the Moon’s surface, such as the ones in this video. Scientists can deduce that regions with fewer craters are relatively younger than regions with more craters. Analysis of the size and distribution of impact craters supports the hypothesis that the Moon was bombarded by two different populations of impactors early in the solar system’s history.