Rockback landscapes


Rockback landscapes are a great place to start when thinking about the possible evolution of the moon. The Moon’s craters look as if they were formed slowly by the action of the tides, and this is reinforced by the discovery of more subtle tidal effects within the lunar crust and upper mantle. The Moon has never completely been a completely symmetric object, but tidal deformations of the crust and mantle must have occurred throughout its long history.

Figure 1: Crater density gradient. The figure shows the gradient of craters per unit radius as a function of radius (black), along with the best-fit crater production rate (blue). In the lower figure the gradient of the best-fit crater production rate is shown as a function of radius (green). The blue and green curves are offset vertically for clarity.

The craters are distributed in a gradient which increases with the distance from the center of the Moon (Figure 1). By comparing this distribution with a theoretical gradient of the tidal potential and the production rate of craters over the past 4.5 billion years, it can be concluded that a great number of craters were produced more than 4.5 billion years ago, when the moon was much denser and its solid interior deformed considerably due to the tidal forces of the Earth.

A closer look at the craters shows that a great number of them are elongated on their long axes, perpendicular to the steepest gradient. This means that the tidal effects of the Earth were concentrated in a specific direction, probably the same direction for all the craters. It could be possible that the Moon never was a perfect sphere, but a slight asymmetry could have existed since its formation, which now is revealed by the tidal patterns. This means that the lunar tidal field may not be the same for all latitudes, which is not surprising since the tides are much weaker than the gravitation due to the Earth.

The shape of the craters can also tell something about the density distribution of the crust. If a material is of high density, a small impact should produce more deep craters than a smaller one. The craters on the Moon show no preference for deeper or shallower craters, which shows that the lunar crust must be relatively sparse and not too rigid.

### 2.3 The Origin of the Surface Texture

The surface of the Moon is roughened and cratered by the effects of solar wind. The lunar crust is probably very thin (about 1.5–2 km) and of low density, similar to a typical volcanic crust. The surface also shows numerous topographic lobes and highlands, and some regions have been eroded to great depths. The topographic features on the Moon are the result of past and present tectonic activity. The Moon is a strongly differentiated body, in that the core is almost completely solid, the crust is much thinner than the Earth's, and it is only about 6 % in thickness. The core and crust are of nearly the same density, so there is a sharp boundary between the two. The outer part of the crust and the core are therefore called the mantle, and the region from the mantle to the outermost crust is called the lithosphere. The boundary between the mantle and the crust is called the core–mantle boundary (CMB), and the mantle–lithosphere boundary (MLB) is the boundary between the mantle and the crust. In a strongly differentiated body like the Moon, the core–mantle boundary is likely to be the most important boundary for the tectonic processes, such as impacts or the transport of heat.

The mantle is probably the oldest part of the Moon. Although the Moon is not known to have had a molten phase, it does have magma generated by volcanism. Such a magma would be trapped in the mantle, and when the Moon was at a warmer and less massive stage it would be a solid. If the Moon formed by accretion of planetesimals, then the mantle of the Moon probably formed first, and the rest of the Moon would grow by differentiation of this solid mantle. It is important to remember that the mantle of the Moon is relatively thin, that is to say, the boundary between the mantle and the crust is not well-defined, that is to say, some of the mantle and some of the crust can exist almost side by side, so a geologist who is not very familiar with the Moon could, in certain circumstances, confuse the two and think that the Moon is composed of two regions. The mantle of the Moon is probably differentiated because the core of the Moon is less massive than the mantle. The Earth's mantle is much more massive than the core, so the core must have formed first and the mantle formed later, as a result of differentiation.

We now come to the question of the structure of the Moon's core. In fact, it

Watch the video: Rockback Breathing Tutorial


Previous Article

Water treatment plant indoor

Next Article

Indoor plants chino cs