Which internal energy source is the most important in continuing to heat the terrestrial planets today?

Question

radioactivity

accretion

differentiation

tidal heating

all of these

Answer 1

Radioactivity.  It is thought that differentiation (heavy elements sinking to the core, kinetic and gravitational potential energy to thermal energy) is long over with as is the majority of accretion (converting kinetic energy from impacting objects into thermal energy) and the terrestrial planets don't experience tidal heating (heat due to flexing in another objects gravitational field, such as Io in Jupiter's orbit).

Answer 2

Radioactivity. It is thought that differentiation (heavy elements sinking to the core, kinetic and gravitational potential energy to thermal energy) is long over with as is the majority of accretion (converting kinetic energy from impacting objects into thermal energy) and the terrestrial planets don't experience tidal heating (heat due to flexing in another objects gravitational field, such as Io in Jupiter's orbit).

Answer 3

Well, they can't ALL be the 'most' important, can they? Tidal heating is only  a major factor on Earth, since the other terrestrial planets don't have large moons. I don't think differentiation adds any heat. Accretion isn't the major factor it was during the formation of the planets. That leaves radioactivity. I'd go with that answer, A, radioactivity.