nearly five to one
The inner planets are small in comparison with the outer . If we represent the sun by a gourd , 20 inches in diameter , Mercury will seem a bilberry -LRB- ₁₆ inch -RRB- Venus , a white currant , the Earth a black currant -LRB- 1/4 inch -RRB- , Mars a red currant -LRB- ⅛ inch -RRB- , the planetoids as fine seed , Jupiter an orange or peach -LRB- 2 inches -RRB- , Saturn a nectarine or greengage -LRB- 1 inch -RRB- , Uranus a red cherry -LRB- 3/4 inch -RRB- , and Neptune a white cherry -LRB- barely 1 inch in diameter -RRB- . By putting the sun and planets in a row , and drawing a contour of the whole , we obtain the figure of a dirk , a bodkin , or an Indian club , in which the sun stands for the knob -LRB- disproportionately big -RRB- , the inner planets for the handle , and the outer for the blade or body . Again , the average density of the inner planets exceeds that of the outer by nearly five to one , but the mass of any planet is greater than the combined masses of all which are smaller than it . The inner planets derive all their light and heat from the sun , and have few or no satellites ; whereas the outer , to all appearance , are secondary suns , and have their own retinue of worlds . On the similitude of a clan or house we may regard the inner planets as the immediate retainers of the chief , and the outer as the chieftains of their own septs or families . '' `` How do you account for the symmetrical arrangement ? ''