Re: Best Sci-Fi Reading for the summer...

James Nicoll <jdnicoll@xxxxxxxxx> wrote:
Most of the mass of Minerva is missing ... most of the material
must have been ejected at speeds faster than Solar escape at 2.5
AU (which just makes the question of where the energy to disrupt
Minerva from that much worse, because now the material needs another
8 km/s ... Wait, no. Higher than that, because not all of the
material will be ejected in the direction of Minerva's motion).

Giving Hogan the benefit of the doubt, it didn't necessarily leave
solar orbit at once. Or even in the first ten thousand years. I seem
to recall that it's been proven that most randomly selected orbits in
the asteroid belt are not stable over the long term. Perturbations
from Jupiter will pump an object's eccentricity up until it either
drops into the sun or makes a close pass to Jupiter and is ejected
from the solar system. Quite possibly the mass of material in the
asteroid belt was once the mass of a planet, but nothing is left
except the small amount that happened to be in a stable resonance
with Jupiter.

Also, Hogan said that disrupting orbits is a side effect of operating
the Ganymean space drive inside a solar system, and that the Ganymeans
did so immediately after the destruction of Minerva, to rescue people
stranded on Luna and ferry them to Earth. With a little handwaving,
that might explain how debris got quickly kicked out the solar system,
how Pluto got into its present orbit, and how Luna got into an
Earth-crossing orbit. But it's not at all clear to me how Earth
subsequently captured Luna into its present near-circular orbit.

However, even just blowing up Minerva is quite an accomplishment. Why
would anyone build a weapon that could do that? That's many, many,
many orders of magnitude more energy than it would take to simply kill
every person and destroy every machine on the planet.

Hogan mentions that Minerva had a thin crust and was more tectonically
active than Earth. He seems to share with Greg Bear the misconception
that planets, like eggs, are held together largely by the strength and
solidity of their hard outer shell, rather than by gravity.

I once worked out that the energy it would take to dismantle Earth
exceeds the energy it would take to *vaporize* Earth. Earth-sized
planets simply aren't going to come apart like an egg or cinderblock
struck with a hammer.

The Moon is just as old as it looks. It just formed somewhere else.
How it formed somewhere else and still managed to look as though
it formed in the same neighborhood as the Earth is an interesting
question.

In all fairness, I'm not sure the fact that Luna is more similar to
Earth than to other planets was known when _Inherit the Stars_ was
written. Neither was it known that Pluto had satellites, that its
density was low, or that there were other Pluto-like worlds in the
outer solar system.
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.
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