Hello, preearth especially, I hope you would like to participate in my new thread.

It seems from your idea (www.preearth.net) that when the two planets collide, the Preearth has to keep most of its crust in the solid state. If it were molten then as it expanded, presumably it wouldn't break into pieces with well defined edges that still have matching shapes today.

I see you and ImagingGeek have both calculated (preearth website and post #34510) the minimum energy released by the two planets combining, based only on potential energy as

Potential energy lost = 10^31 J

You've also calculated a temperature increase of 3500 degC.

And that's where it seems to stop.

This still doesn't answer the important question of whether the crust would melt or not. How about some of these possiblities?

1) The heat is applied instantaneously everywhere leading to temperature of 3500degC and complete melting of the entire earth (1200degC melting point for crust).

2) The heat is applied under the surface and is conducted through the crust then radiated into space slowly enough that the crust never reaches melting point.

3) The collision occurs slowly so the heat is radiated into space before the crust ever reaches melting point.

4) Any other possibilities?