For a point mass acting as a source of a g field we draw lines that point inwards from infinity. Where we have an extended body like a planet, I've always drawn the field lines terminating on the surface. However, I've seen a question in an exam paper that implies that it's okay to continue drawing the field inside the planet with the lines getting closer together before meeting in the middle. Surely this is what the field looks like for a singularity. Inside the planet, the field falls away linearly to zero at the centre. This being the case, it seems to me that you can't just keep drawing the field lines getting closer together as increasing the density of the lines represents an increasing field strength. What bothers me is that the field lines inside the planet all still need to point towards the centre, so it's difficult to imagine the patten. My best guess is that because the lines need to end on a mass, you get a picture where the lines are always radial and get closer together inside the planet BUT, as we move inwards, some of the lines terminate and the overall density of filed lines goes down. Is this right?