>>>>> Our moon'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 moon's extremely thick coating of
>>>>> surface ice that existed prior to the lithobraking encounter with
>>>>> Earth. I'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 that'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
>>>>> it's tidal radius grip on such planets and spare moons or any number
>>>>> of planetoids.
>>>>>
>>>>> Basically, of what I'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
