A vector is a mathematical construct that has magnitude and direction. The cross product of two vectors is a binary operation in three-dimensional space that results in a third vector that is ...
In the present situation, both Earth and Mars are moving in the same direction around the Sun, but the slower one, Mars, appears to move backwards compared to the faster one, Earth. Just an illusion. The retrograde motion of Mars â like the apparent motion of the slower car on the highway â is nothing more than an illusion.
One reason is that Mars doesn't now because the interior is too cold for the convection currents in the mantle that drive the movement of plates. It is also too cold for a molten core to generate a strong magnetic field to protect the surface form radiation and keeps the atmosphere intact. In the past, Mars might have had a warmer interio with a molten core, and so a strong magnetic field and more geological activity. A reason why Mars wouldn't have plates anyway is the theory that planets less massive than Earth are not massive enough for plates to form. Planets the Earth's size still require a large mass like the Moon for plate tectonics, while larger planets do not necessarily require a large moon.