>>> Our moonÂ’s South Pole Aitken basin of 2500 km in diameter is currently
>>> only 13 km deep (roughly 0.5%%), offers a perfectly darn good example of
>>> the relatively shallow nature of such a horrific impact, as most likely
>>> moderated in crater depth due to the moonÂ’s extremely thick coating of
>>> surface ice that existed prior to the lithobraking encounter with
>>> Earth. IÂ’d roughly estimated a Guth SWAG of 262 km worth of surface
>>> ice, although it certainly could have been packing as much depth as a
>>> good 1000 km worth of salty ice.
>>>
>>>
http://en.wikipedia.org/wiki/South_Pole-Aitken_basin
>>>
http://en.wikipedia.org/wiki/Image:Aitken_clem_big.gif
>>>
>>> Of course, Earth too had a relatively thin layer of surface ice, plus
>>> likely a 10 bar atmosphere at the time of this icy and lithobraking
>>> encounter.
>>>
>>> Of several other largest of craters are those approximately 10%% as
>>> impressive, or roughly 200 km in diameter, and somewhat equally as
>>> unusually shallow.
>>>
>>> Otherwise, if not having been protected by a thick layer of salty ice,
>>> I suppose those unusually shallow and clearly oldest of moon craters
>>> are due to the unusually robust crust that is simply a whole lot
>>> thicker and more density substantial than most anything of terrestrial
>>> crust.
>>>
>>> In order to have produced the South Pole-Aitken basin of 2500 km by 13
>>> km would also have required an impact with something of considerably
>>> larger diameter, such as Earth or possibly Mars got in the way before
>>> that moon arrived at encountering Earth.
>>>
>>> Once again, a good supercomputer could have nicely simulated this type
>>> of complex multiple encounter with such an icy proto-moon or icy
>>> planetoid that was merging with our solar system after being red-giant
>>> phase ejected away from the complex Sirius-A/B star/solar system that
>>> had recently burned through 5x worth of solar mass upon converting
>>> Sirius-B into that white dwarf (Sirius-A capable of picking up one
>>> solar mass, leaves 4x thatÂ’s missing in action).
>>>
>>> Of course, for all we know, Earth or at least Venus may also have been
>>> deployed into orbiting Sol by way of that same analogy of the Sirius
>>> star system having lost those 4x solar units of mass, thereby losing
>>> itÂ’s tidal radius grip on such planets and spare moons or any number
>>> of planetoids.
>>>
>>> Basically, of what IÂ’m suggesting by way of this topic is; if our
>>> icy proto-moon had not encountered something of a Mars or Earth like
>>> orb, as such it would not have gotten that shallow South Pole Aitken
>>> crater basin, and most likely Earth would not have its seasonal tilt
>>> established, or having subsequently thawed out from the very last ice-
>>> age this Earth w/moon is ever going to see. - Brad Guth Brad_Guth
>>> Brad.Guth BradGuth
