a-planets - erratum and additional musings

[snikt]
> If we are talking about "artificial planets" built with yet-to-be-invented
> super-materials, then I think that the best option would be a cylinder
> *without* endcaps properly said. Suppose an artificial planet 9 Mm in
> diameter and in length - the surface area of this thing would be the
*same*
> of Earth (oceans included), and the a-planet would be able to sustain
> billions of inhabitants. Well, the borders of the cylindrical surface
would
> not be straight, but instead they would curve gently upward and then
inward
> the cylinder, in a semicircular curve 100 Km in diameter. The whole
> atmosphere would be contained inside the limits of the curved borders as
> water is contained inside a bowl.
[snikt]

I'm sorry, it seems that I messed up radius with diameter somewhere in my
calculations. A cylinder with its length equal to its diameter and with a
surface area equal to that of Earth itself would have the *same* diameter as
Earth, that is, 12.76 Mm ...

Talking a little more about a-planets, I mused about how much matter it
would take to make and "Earth-sized" a-planet. First, I assumed a
cylindrical "crust" just a hundred metters thick. Why a hundred metters?
First, its is a nice round number ;-); second, it would allow shallow oceans
that would, on the other hand, be deep enough for the use of very large
ships; and, finally, even a one-megaton nuke wouldn't be able to puncture a
hole on a crust that thick... (And, since a-planets depend upon the
existence of supermaterials, I guess that any puncture would need a *really*
big nuke.) Using that thickness, and assuming that your raw materials are
100% used either in the form of structural support of just for making soil
and mountains and oceans, then an Earth-sized a-planet would consume an
asteroid with a diameter of 460 Km .

That is certainly a *big* asteroid, and there is just a handful of them in
the Asteroid Belt. However, the estimates for the Kuipier Belt are around
30,000 objects with diameters over 100 Km, and so it seems reasonable to
supose that there are a few hundreds of asteroids big enough out there to
produce the same number of a-planets. Of course, since the Kuipier Belt is
just *so* far away from the Sun, that mirror system that I proposed would be
difficult to use. Perhaps some sort of hydrogen-fusion "articial sun"
shinning at the geometric center of the a-planet would be the best
solution...

Lucio Coelho