loss, with additional change possible if there is a secular variation of the gravitational
constant, G. The measurement of the change of scale could provide insight into the past and
the future of the solar system, and in addition a better understanding of planetary motion and
fundamental physics. Estimates for the expansion of the scale of the solar system are of
order 1.5 cm year− 1 AU− 1, which over several years is an observable quantity with present …