Improved Test of the Equivalence Principle for Gravitational Self-Energy

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, Δa_CD/a_s  =  (+0.1±2.7±1.7)×10^-13, and lunar-ranging data provide an unambiguous test at the 1.3×10^-3 level.