Arabia Quadrangle - Craters

Craters

Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. As craters get larger (greater than 10 km in diameter) they usually have a central peak. The peak is caused by a rebound of the crater floor following the impact. Sometimes craters display layers. Since the collision that produces a crater is like a powerful explosion, rocks from deep underground are tossed unto the surface. Hence, craters can show us what lies deep under the surface.

Some craters in Arabia are classified as pedestal craters. A pedestal crater is a crater with its ejecta sitting above the surrounding terrain and thereby forming a raised platform. They form when an impact crater ejects material which forms an erosion resistant layer, thus protecting the immediate area from erosion. As a result of this hard covering, the crater and its ejecta become elevated, as erosion removes the softer material beyond the ejecta. Some pedestals have been accurately measured to be hundreds of meters above the surrounding area. This means that hundreds of meters of material were eroded away. Pedestal craters were first observed during the Mariner missions.

• Pedestal craters and layers in Tikonravev Crater in Arabia, as seen by Mars Global Surveyor (MGS), under the MOC Public Targeting Program. Layers may form from volcanoes, the wind, or by deposition under water. Some researchers believe this crater once held a massive lake.

• Pedestal craters form when the ejecta from impacts protect the underlying material from erosion. As a result of this process, craters appear perched above their surroundings.

• Drawing shows a later idea of how some pedestal craters form. In this way of thinking, an impacting projectile goes into an ice-rich layer—but no further. Heat and wind from the impact hardens the surface against erosion. This hardening can be accomplished by the melting of ice which produces a salt/mineral solution thereby cementing the surface.

• Pasteur Crater Floor, as seen by HiRISE. The scale bar is 1,000 meters long

• Henry Crater Mound, as seen by HiRISE. The scale bar is 500 meters long

• Mounds in craters like Henry are formed by the erosion of layers that were deposited after the impact.

• Crater in the middle of Cassini, as seen by HiRISE. Layers may have been deposited under water since it is believed that Cassini once held a giant lake.

• Masursky Crater Floor, as seen by HiRISE.

• New crater, as seen by HiRISE under HiWish program. The new crater indicated with the white arrow is about 10 yards across and was probably created by the collision with an object the size of a large watermelon. This crater did not appear in earlier images of the same region.