LuV The/Chapter I

ONE EXTENSIVE EVIDENCE

We all know that the closest space sphere to Earth is its only natural satellite. At nights the Moon shines to us with reflected rays of the Sun, so that everyone can watch how it crosses the dark dome of the sky. One thing we can't see is the far side of the Moon, since it's always turned to viewers on Earth only by one side.

There are plenty of craters with different diameters on the lunar surface. But the largest and deepest one has been kept dark on that unseen side until we developed spacecraft that can reach there.

Blue depicts an area of low elevation, which is called the South Pole–Aitken basin

We are talking about the South Pole–Aitken basin. What do we undoubtedly know about this crater? It has a diameter more than 2000 km. The lowest depth is 8.2 km. Crustal thickness is about 30 km beneath the floor of this basin, which is 2 times thicker than areas around it.

According to Wikipedia, it is estimated that the basin was formed approximately 4.2 to 4.3 billion years ago. And according to Mohit and Phillips (2006) we can say that this basin has experienced very little relaxation of its crustal structure since formation. This is to say that we see almost the same appearance of it that was initially.

We can say that the basin's rim extends from the Moon's South Pole till the Aitken crater, due to this fact the basin gained its current name. It is believed that some elevations near the Pole, which are partially visible from Earth during favourable librations, belong to rim of the basin. Before the astronautics era has begun this feature was sometimes referred to as Leibnitz mountains. Just few years ago the highest peak of it gained a new name – Mons Mouton. Being one of the tallest points on the Moon this flat-topped mountain has 6 km in height.

There is another one geologic ring inside the basin with smaller diameter, but with the same center. Scientists usually call the area within it the Inner Terrane, and the area between walls of this two rings – the Outer Terrane. So it is some kind of a multi-ringed basin.

The precise shape of the basin is disputable.

Simulation of impact crater formation

Garrick-Bethell and Zuber (2009) insist upon its elliptical structure. But the latest data collected by University of Maryland scientists suppose more circular shape.

On what real shape has the crater depends whether the forming impact was vertical or oblique. Many researchers assume the oblique impact because the vertical impact scenario means that large volumes of mantle would be exposed at the surface. But the survey data does not approve that.

Kaguya mission indicated some 15 years ago that a crustal thickness at the center of the crater was 30 km. It is about twice thinner than the lunar average. But still too much even for oblique impact. So it was proposed that an impactor caused melting of all excavated materials, including crust and upper mantle, which then differentiated and re-crystallised to the surface structure we see now.

One interesting thing is that we can't definitely point on any central peak, which usually has a form of well seen bulge on some other craters (for ex, on Mercury's Caloris basin or on Mimas' Herschel crater). Within the theory, that was briefly described one intend earlier, it is postulated that a large melt pool appeared in the center of the impact zone; in this pool main part of ejecta melted till achieving plain surficial condition. I'd say this impact had incredibly huge energy within this theory.

What if we will propose another theory that do not require any fancy of melting pool and energy-reducing manipulations with trajectory. Let's imagine that the astronomical body was covered by ice. We should say that ice was the uppermost layer of this sphere. And when the great impact happened to the Moon, this solid but brittle layer softened catastrophic interaction between the two bodies. It also prevented the impact area from heating and explosive scattering of any ejecta, as well as from forming an elevated structure in the bull's-eye zone. This also will explain why this immense basin has so unclear appearance and boundaries, since the icy crust made it unable to excavate very deep.

So, even vertical impact in high velocities will not require any mantle exposition within this scenario. Moreover, complicated structure of the body suits the most common reason for nested craters formation.

Such theory should not be considered as an exotic one, because we do know about existence of ice-covered bodies like this within the Solar System.

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This is chapter I.

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