As a result of mantle convection heat is able to efficiently escape from the Earth's deep interior to the surface, where it is deposited into the atmosphere—ocean system and eventually radiated to space.
All the factors like the planet falling under the influence of the sun's gravity., and the planet changes its speed along its orbit, the planet changes its distance from the sun. As described by the Kepler's Second Law the planets become weaker when it travels farther away from the sun.