-Z- (Z@Gundam.Com)
Wed, 24 May 2000 18:23:44 -0700

At 12:49 5/24/2000, you wrote:
>At 20:21 05/23/2000 -0400, core@gundam.com wrote:
>>Can't comment on the 500km crater size, but the problem of crater size as
>>a function of the dropped body has been solved. For example, you can look
>>at a crater on the Moon or Mars or Earth and give a very good estimate of
>>the meteorite. So given the approximate mass of a colony, the crater size
>>should be known. Is there a planetary astronomer in the house?
> Rule of thumb from my astronomy course -- the size of the crater is
>10x that of the object's diameter, and the depth 1.5-2x. That means the
>impacting object of a 500km object is about 50km in diameter, and will cause
>a 75km deep crater -- won't that let the magma out?

Yes, but it'll also let the ocean in. Lots of steam will probably be
produced during the first hour or so, until enough sea water fills the
crater to seal off the breach, turning it into an undersea
volcano. Thereafter, the crust may "heal" or not -- I can see it going
either way.

With only a 10:1 ratio like that, I can't see getting a 500km crater out of
even a whole 32km colony and we're not even getting that. Sydney was hit
by the surviving (at best) half of a colony that was broken up over the
Indian Ocean. The remainder rained down in smaller chunks across North

Assuming that both the docking bay block and the industrial block -- the
largest and most solid pieces of the colony -- hit Sydney, that's still
only about two cubic kilometers of material. Assume that about half the
mass of the cylinder crumpled up into a ball and fused with the bay and
industrial blocks and you could double that.

Since the colony re-entered the atmosphere and fell like any other
de-orbiting object, it's speed is limited to orbital re-entry speeds, so
you can't compensate for the lack of mass by jacking up the velocity.

It looks like we should be talking about a 50km, not a 500km, crater.

Unless maybe the Zeon packed the colony with nukes before they dropped it?

> Can't tell how the shape of a colony will affect this though..

The mass and velocity will play a more important role than the shape. The
shape of the colony would affect the shape of the crater, as would its
angle of impact, but I don't think it would affect the size of the crater.


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