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The rim or edge of an
The rim or edge of an impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
is the part that extends above the height of the local surface, usually in a circular or elliptical pattern. In a more specific sense, the rim may refer to the circular or elliptical edge that represents the uppermost tip of this raised portion. If there is no raised portion, the rim simply refers to the inside edge of the curve where the flat surface meets the curve of the crater bottom.
Simple craters
Smaller, simple craters retain rim geometries similar to the features of many craters found on theMoon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...
and the planet Mercury.
Complex craters
Large craters are those with a diameter greater than 2.3 km, and are distinguished by central uplifts within the impact zone. These larger (also called “complex”) craters can form rims up to several hundred meters in height. A process to consider when determining the exact height of a crater rim is thatmelt
Melt may refer to:
Science and technology
* Melting, in physics, the process of heating a solid substance to a liquid
* Melt (manufacturing), the semi-liquid material used in steelmaking and glassblowing
* Melt (geology), magma
** Melt inclusions, ...
may have been pushed over the crest of the initial rim from the initial impact, thereby increasing its overall height. When combined with potential weathering due to atmospheric erosion over time, determining the average height of a crater rim can be somewhat difficult. It has also been observed that the slope along the excavated interior of many craters can facilitate a spur
A spur is a metal tool designed to be worn in pairs on the heels of riding boots for the purpose of directing a horse or other animal to move forward or laterally while riding. It is usually used to refine the riding aids (commands) and to ba ...
-and-gully
A gully is a landform created by running water, mass movement, or commonly a combination of both eroding sharply into soil or other relatively erodible material, typically on a hillside or in river floodplains or terraces. Gullies resemble la ...
morphology, including