I added a layer of dense neutron matter and radioactive material to the initial formation of the prison / planet.
A hollow planet would not form naturally, nor would its "inside" have an appropriate gravity, unless there was a compensating mass which directed the force of gravity "down" when standing on either surface. I believe this would also leave the center gravity free, but I am not a physicist.
A massive collision with this sphere early on - a moon or small planet? - would also provide the crack discussed in the next section, and may also "melt" the neutron material sufficiently for small holes to appear at the poles, also as described later.
The radioactive material was added to provide material for plate tectonics, continental drift, volcanoes, nuclear power / weapons, decay by-products such as lead and helium, and - more importantly - to create that necessary magnetic field which prevents the solar wind from stripping the planets' atmosphere. I suspect its probably not enough to create an earth-like field, but perhaps it reenforces an existing magnetic field set up as part of the prison.
I added a layer of dense neutron matter and radioactive material to the initial formation of the prison / planet.
A hollow planet would not form naturally, nor would its "inside" have an appropriate gravity, unless there was a compensating mass which directed the force of gravity "down" when standing on either surface. I believe this would also leave the center gravity free, but I am not a physicist.
A massive collision with this sphere early on - a moon or small planet? - would also provide the crack discussed in the next section, and may also "melt" the neutron material sufficiently for small holes to appear at the poles, also as described later.
The radioactive material was added to provide material for plate tectonics, continental drift, volcanoes, nuclear power / weapons, decay by-products such as lead and helium, and - more importantly - to create that necessary magnetic field which prevents the solar wind from stripping the planets' atmosphere. I suspect its probably not enough to create an earth-like field, but perhaps it reenforces an existing magnetic field set up as part of the prison.