A

M Rpm

showing indeed that as R decreases the ratio increases. Thus, in a sufficiently small body, from early in its history, any active energy sources will have been unable to compensate the energy losses, so the interior temperatures will have declined, and the interior will already be at temperatures determined by absorbed solar radiation and emitted IR radiation.

Question 4.11

Describe qualitatively the present-day temperature versus depth in a hypothetical planetary body if its sole energy source (apart from solar radiation) has always been each one of the following:

(a) Accretional energy confined to its surface.

(b) Long-lived radioactive isotopes confined to a small central core.

(c) As for (b), but in a body that is a scaled-up version of that in (b).

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