Solar system expansion and strong equivalence principle as seen by the NASA MESSENGER mission

Abstract

The NASA MESSENGER mission explored the innermost planet of the solar system and obtained a rich data set of range measurements for the determination of Mercury's ephemeris. Here we use these precise data collected over 7 years to estimate parameters related to general relativity and the evolution of the Sun. These results confirm the validity of the strong equivalence principle with a significantly refined uncertainty of the Nordtvedt parameter η = (-6.6 ± 7.2) × 10-5. By assuming a metric theory of gravitation, we retrieved the post-Newtonian parameter β = 1 + (-1.6 ± 1.8) × 10-5 and the Sun's gravitational oblateness, J2 J 2= (2.246 ± 0.022) × 10-7. Finally, we obtain an estimate of the time variation of the Sun gravitational parameter, MGMG M ° G M= (-6.13 ± 1.47) × 10-14, which is consistent with the expected solar mass loss due to the solar wind and interior processes. This measurement allows us to constrain GGG ° G to be <4 × 10-14 per year.