|What about the Moon ?|
Comets and asteroids strike the Moon at
a wide range of impact speeds, (with a typical speed of 20
kilometers per second) producing craters with diameters 10 to 20
times larger than the impacting object. As always crater
morphology depends on the impactor size.
An important fact about the Moon is its absence of atmosphere: in this way craters are preserved much better than on Earth and even very old craters are still visible..
Morphology of craters on the moon
Simple Moon craters have rim diameters
of less than about 15 kilometers, while diameters larger than
about 15 kilometers. This value
Complex craters on the Moon have diameters greater than 15 Km and can present different characteristic and complex forms (including shallow, relatively flat floors, central uplifts, and slump blocks and terraces on the inner wall of the crater rim):
|Moltke Crater, 7 kilometers in diameter, is an
excellent example of a simple crater with a bowl-shaped
interior and smooth walls.
(NASA: Apollo 10 photograph AS10-29-4324.)
|Bessel Crater, 16 kilometers in diameter and 2
kilometers deep, is a typical transitional crater between
simple and complex. The bowl-shaped structure has been
destroied by slumping of material from the inner part of
the crater rim.. However, wall terraces and a central
peak have not developed.
(NASA:Apollo 15 Panoramic photograph AS15-9328.)
|Euler Crater, 28 kilometers in diameter and about 2.5
kilometers deep, is a complex crater morphology. It has a
flattened floor, a small central peak, and material that
has slumped off the inner crater rim. The blanket of
ejecta surrounding the crater is quite visible.
(NASA: Part of Apollo 17 Metric photograph AS17-2923.)
|King Crater, on the Moon's farside, is 77 kilometers
in diameter and more than 5 kilometers deep. It is a
typical large lunar crater, with terraces and slump
blocks on the inside of the crater rim and a relatively
flat floor .
(NASA: Apollo 16 Metric photograph AS16-1580.)