Figure 1. Contours of the Roche potential for a mass ratio of 1/1000, typical of a giant planet similar to Jupiter orbiting a star similar to the Sun. The planet is in a circular orbit in the xy plane around the center of mass of the system, which is located at the origin (far to the left of the plot), close to the center of the star. The unit of length is the orbital separation. The closed part of the red contour is a cut through the Roche lobe (or Hill sphere), which delimits the region in which material co-orbiting with the planet is bound to it, and reaches the inner Lagrangian point L1. The blue contour is a slightly higher equipotential that crosses the outer Lagrangian point L2.