why do small planets lose internal heat faster than large planets
Internal heating Internal heat is the heat source from the interior of celestial objects, such as stars, brown dwarfs, planets, moons, dwarf planets, and (in the early history of the Solar System) even asteroids such as Vesta, resulting from contraction caused by gravity (the Kelvin–Helmholtz mechanism), nuclear fusion, tidal heating, core solidification (heat of fusion released as molten core material solidifies), and radioactive decay. The amount of internal heating depends on mass; the more massive the object, the more internal heat it has; also, for a given density, the more massive the object, the greater the ratio of mass to surface area, and thus the greater the retention of internal heat.[citation needed] The internal heating keeps celestial objects warm and active.
Jupiter Jupiter's mass is 2.5 times that of all the other planets in the Solar System combined—this is so massive that its barycenter with the Sun lies above the Sun's surface at 1.068 solar radii from the Sun's center.[32] Jupiter is much larger than Earth and considerably less dense: its volume is that of about 1,321 Earths, but it is only 318 times as massive.[6][33] Jupiter's radius is about 1/10 the radius of the Sun,[34] and its mass is 0.001 times the mass of the Sun, so the densities of the two bodies are similar.[35] A "Jupiter mass" (MJ or MJup) is often used as a unit to describe masses of other objects, particularly extrasolar planets and brown dwarfs. So, for example, the extrasolar planet HD 209458 b has a mass of 0.69 MJ, while Kappa Andromedae b has a mass of 12.8 MJ.[36]