Impact Craters Lab

Name: ______________________________ Name: ______________________________ Name: ______________________________ Name: ______________________________ Per: _________ Date: _____________________ Impact Craters Lab Purpose: To determine the factors affecting the appearance of impact craters and ejecta. Background: The circular features so obvious on the Moon’s surface are impact craters formed when impactors smashed into the surface. The explosion and excavation of materials at the impact site created piles of rock (called ejecta ) around the circular hole as well as bright streaks of target material (called rays ) thrown for great distances. Two basic methods forming craters in nature are: 1) impact of a projectile on the surface and 2) collapse of the top of a volcano creating a crater termed caldera . By studying all types of craters on Earth and by creating impact craters in experimental laboratories geologists concluded that the Moon’s craters are impact origin. The most common topographic features on Mercury are the craters that cover much of its surface. Although lunar like in general appearance, Mercurian craters show interesting differences when studied in detail. Mercury’s surface gravity is more than twice that of the Moon, partly because of the great density of the planet’s huge iron - sulfur core. The higher gravity tends to keep material ejected from a crater from traveling as far—only 65 percent of the distance that would be reached on the Moon. This may be one factor that contributes to the prominence on Mercury of secondary craters—those craters made by impact of the ejected material, as distinct from primary craters formed directly by asteroid or comet impacts. The factors affecting the appearance of impact craters and ejecta are the size and velocity of the impactor, and the geology of the target surface. By recording the number, size, and extent of erosion of craters, lunar geologists can determine the ages of different surface units on the Moon and can piece together the geological history. This technique works because older surfaces are exposed to impacting meteorites for a longer period of time than are younger surfaces. Impact craters are not unique to the Moon. They are found on all the terrestrial planets and on many moons of the outer planets and on many moons of the outer planets. On Earth, impact craters are not as easily recognized because of weathering and erosion. Famous impact craters on Earth are Meteor Crater in Arizona, U.S.A.; Manicouagan in Quebec, Canada; Sudbury in Ontario, Canada; Ries Crater in Germany, and Chicxulub on the Yucatan coast in Mexico. Chicxulub is considered by most scientists as the source crater of the catastrophe that led to the extinction of the dinosaurs at the end of the Cretaceous period. An interesting fact about Chicxulub crater is that you cannot see it. Its circular structure is nearly a kilometer below the surface and was originally identified from magnetic and gravity data.

Name: ______________________________ Name: ______________________________ Name: ______________________________ Name: ______________________________ Per: _________ Date: _____________________ raised rim- rock thrown out of the crater and deposited as a ring-shaped pile of debris at crater’s edge during the explosion and excavation of an impact event. floor- bowl shaped or flat, characteristically below surrounding ground level unless filled in with lava. central uplifts- mountains formed because of the huge increase and rapid decrease in pressure during the impact event. They occur only in the center of craters that are larger than 40 km diameter. See Tycho crater for another example. walls- characteristically steep and may have giant stairs called terraces. ejecta- blanket of material surrounding the crater that was excavated during the impact event. Ejecta becomes thinner away from the crater. rays- bright streaks starting from a crater and extending away for great distances. See Copernicus crater for another example.