S (the synodic period) = 360 / (360/ P - 360/365.256) days. S (the synodic period) = 360 / (360/365.256 - 360/ P) days. A diagram showing the relationship between orbital size and synodic periods. As the planets move around the Sun they change their positions relative to each other.
Some geologists consider that mantle plumes are generated in the lower levels of the asthenosphere by the decay of concentrations of radioactive isotopes. However, many believe that they are generated at much deeper levels in the lower mantle, perhaps even at the boundary of the mantle with the outer core.
Heat transferred from the plume raises the temperature in the lower lithosphere to above melting point, and magma chambers form that feed volcanoes at the surface. This area is also known as a hot spot. Because the plume remains anchored at the core-mantle boundary, it does not shift position over time.