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.
Spreading center volcanism occurs at the site of mid-oceanic ridges, where two plates diverge from one another. As the plates are pulled apart, hot asthenosphere rises upward to fill voids of the extended lithosphere. The rise of this hot mantle provides thermal buoyancy to the ridge area and this is the reason that they stand as high ridges in the center of ocean basins. This is demonstrated in the colored relief images shown here. Mid-oceanic ridge of the south Pacific. As the hot asthenosphere rises to shallow levels, it decompresses and melts to produce basalt magmas. These magmas pond in crustal magma chambers where they are periodically tapped by vertical fractures that provide conduits for the rapid rise of magma to the surface.