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Re: starship-design: Ice Impact Terraforming
> If impact speeds are effectively moderated that no ejecta escape, the
> physical properties of the target body are not relevant to its inertial
> relationships. If torque is applied to a body made of powder, it will spin.
If the impact speeds are low enough to avoid blowing ejecta into space,
then the mass of impactors needed to substantially increase the Moon's
rotational rate will be a substantial fraction of the Moon's mass. If
the impact speeds are higher, then you'll mostly blow a lot of energy
throwing ejecta into space and heating the lunar surface without
affecting its rotation substantially.
As it is the existing rotation of planets is left over from their
formation, and has not been substantially affected by any subsequent
impacts. In some cases tidal coupling (such as between Earth and its
Moon or Jupiter and its inner moons) has produced resonance -- over
billions of years.
Probably the biggest problem with terraforming Venus is not making the
atmosphere breathable, but changing Venus's rotation rate into something
that will produce tolerable weather.