Roche Limit Calculator

Body Type selects between two different constants in the underlying formula: a larger constant for fluid bodies, which deform easily and disrupt farther out, and a smaller constant for rigid bodies, which resist deformation and can orbit closer in before breaking apart. That constant multiplies the entire result, so switching between Fluid and Rigid changes the computed Roche Limit by close to a factor of two near the default inputs, even though it doesn't touch Primary Radius or either density value.

Primary Radius has the largest effect across the calculator's declared input ranges, because the Roche Limit scales directly (one-to-one) with it. Primary Density and Secondary Density only enter the formula through a cube root of their ratio, so even a large percentage change in either density produces a much smaller percentage change in the computed Roche Limit than the same percentage change in Primary Radius does.

The formula uses the ratio of primary density to secondary density raised to the one-third power -- a denser secondary body (higher Secondary Density) makes that ratio smaller, which shrinks the Roche Limit. Physically, a denser body holds itself together with stronger self-gravity for its size, so it can survive tidal forces at a closer orbital distance than a less dense body of the same size would.

No. This is a simplified two-body approximation that treats the primary and secondary as idealized spheres and ignores the secondary's rotation, orbital eccentricity, and internal structure -- all of which shift a real body's actual disruption distance in practice. Treat the result as an order-of-magnitude estimate rather than a precise prediction for any specific real satellite or moon.