In article ,
"Jason Who" writes:
...I was hoping for an model of astronomical phenomena
which was in itself simple, but which were perhaps hard to implement and
test numerically.

Not easy to find, I'm afraid. Not all astronomers are bad
programmers. :-)

I wonder whether there's something to be done in N-body work
simulating the long-term stability of the solar system. That was
popular about 15 years ago, but I haven't seen anything lately. One
group even constructed a special-purpose computer, the "digital
orrery." I don't know whether this area could turn into a project,
but there may be something to consider.

Oops... I see there's work being done on this after all. A quick
check with ADS shows a paper by Batygin & Laughlin (2008 ApJ 683,
1207) that forward-integrates the planets for 20 Gyr. (Bottom line:
the solar system is stable or at least there are no "severe"
instabilities. Phew!) There may still be a project here; I haven't
looked at details.

In general, when
modelling high velocity impacts, using SPH you consider the solid a fluid. I
would consider the gigantic impact into the proto earth as high velocity...

Yes, "liquid forces" would probably have been a better phrase for me
to use. Anyway, you need something to keep the simulated Earth and
incoming body from collapsing to point masses and also to allow
"drops" to stick together after the collision but have finite radius.

Gently placing a big asteoroid on the surface of Earth would, I
would imagine, cause it to sink into the Earth untill it "floats".

In fact, one can estimate the size of mountains by knowing the
average strength of crustal rock and the Earth's surface gravity. So
indeed any object bigger than a mountain should do as you say.
Everyday experience is not a good guide at large scales!

Feel free to email me off-list if you wish.

--
Steve Willner Phone 617-495-7123
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