Is convection realizable in solids and in vacuum?

During convection, heat is transferred by jets and streams of gas or liquid in the field of gravitational forces. Convection is possible where there are more and less heated portions of liquid or gas. Due to the difference in density, the warmer layers float up, the less heated ones go down, heat up and repeat the cycle again. In a solid, streams and jets are impossible. Consequently, convection is not feasible in a solid. In a vacuum, convection is also impossible, since there is nothing there that could act as a coolant.
Answer: Convection in solids and in vacuum is not feasible.