Lunar Craters - Characteristics

Characteristics

Because of the Moon's lack of water, and atmosphere, or tectonic plates, there is little erosion, and craters are found that exceed two billion years in age. The age of large craters is determined by the number of smaller craters contained within it, older craters generally accumulating more small, contained craters.

The smallest craters found have been microscopic in size, found in rocks returned to Earth from the Moon. The largest crater called such is about 360 kilometers (220 mi) in diameter, located near the lunar South Pole. However, it is believed that many of the lunar maria were formed by giant impacts, with the resulting depression filled by upwelling lava.

Craters typically will have some or all of the following features:

• a surrounding area with materials splashed out of the ground when the crater was formed; this is typically lighter in shade than older materials due to exposure to solar radiation for a lesser time
• raised rim, consisting of materials ejected but landing very close by
• crater wall, the downward-sloping portion of the crater
• crater floor, a more or less smooth, flat area, which as it ages accumulates small craters of its own
• central peak, found only in some craters with a diameter exceeding 16 miles (26 km); this is generally a splash effect caused by the kinetic energy of the impacting object being turned to heat and melting some lunar material.