Improved Test of the Equivalence Principle for Gravitational Self-Energy

Abstract

The lunar-ranging test of the equivalence principle for gravitational self-energy is ambiguous. Although the Earth has more gravitational self-energy than the Moon, its sizable Fe/Ni core also gives it a different composition than the Moon. We removed this ambiguity by comparing, in effect, the accelerations of ``miniature'' earths and moons toward the Sun. Our composition-dependent Earth-Moon acceleration, $\ensuremath{\Delta}{a}_{\mathrm{CD}}/{a}_{\mathrm{s}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(+0.1\ifmmode\pm\else\textpm\fi{}2.7\ifmmode\pm\else\textpm\fi{}1.7)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$, and lunar-ranging data provide an unambiguous test at the $1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ level.