On Sat, Jun 25, 2016 at 11:05:31PM +0200, Knapp wrote:
> > Not noticeably.  In the specific case of Earth, the Moon would leave
> > orbit unless engineered to remain.
>
> How would you do that? Make it hollow too?

Mostly move it in closer.  There are two reasons: first is that a much
less massive Earth has much weaker gravity, so if the Moon was moving
at the same speed it would exceed escape velocity and go into
independent orbit of the Sun.  Second is that even at a lower speed,
the Sun's gravity gradient would destabilize a distant orbit pretty
quickly.

Though probably you'd want to reduce the Moon's mass as well,
otherwise it would outmass the hollow Earth, and the Earth would be
more orbiting the Moon than the reverse.  The closer orbit would also
greatly multiply tides on Earth if the Moon retained the same mass.

- Tim