Planetary ephemerides and gravity tests in the solar system

We review here the tests of fundamental physics based on the dynamics of solar system objects.

💡 Research Summary

The paper provides a comprehensive review of how the dynamics of solar‑system bodies are used to test fundamental physics, focusing on the construction and application of planetary ephemerides. It begins by outlining the theoretical motivation: general relativity (GR) predicts precise relationships among the equivalence principle, spacetime curvature, and the constancy of the gravitational constant G. Solar‑system dynamics, because of the long time baselines and high‑precision tracking, constitute the most stringent laboratory for probing these predictions.

The authors then describe the major ephemeris families—INPOP, DE, and EPM—detailing how each incorporates the masses of the Sun, planets, and the most massive asteroids, the solar quadrupole moment (J₂), relativistic corrections expressed in the parametrized post‑Newtonian (PPN) framework, and a collective model for the asteroid belt. The construction process relies on a massive least‑squares fit to a heterogeneous data set that includes laser ranging to the Moon (LLR), radar and optical astrometry of planets and moons, and radio‑tracking (range and Doppler) of deep‑space probes such as Cassini, MESSENGER, Juno, and the upcoming BepiColombo mission.

By jointly fitting these observations, the ephemerides yield tight constraints on several key parameters. The PPN parameters γ and β are determined to be 1 + (2.1 ± 2.3) × 10⁻⁵ and 1 + (1.5 ± 1.8) × 10⁻⁵ respectively, confirming GR at the 10⁻⁵ level. The time variation of G is limited to |Ġ/G| < 7 × 10⁻¹⁴ yr⁻¹, effectively ruling out many scalar‑field cosmologies that predict larger drift rates. Tests of the weak equivalence principle, expressed through the Nordtvedt parameter η, give η < 10⁻⁴, indicating that the Earth‑Moon‑Sun system falls freely with no detectable composition‑dependent acceleration. The solar J₂ is measured as (2.25 ± 0.12) × 10⁻⁷, in agreement with helioseismic models of solar interior rotation.

A substantial portion of the review is devoted to the treatment of asteroid perturbations. The authors explain how a combination of mass‑determination from spacecraft fly‑bys, asteroid occultations, and a statistical mass‑density model reduces the uncertainty in the collective asteroid gravity to a few tens of meters in planetary range residuals. This refinement is crucial for long‑term ephemeris accuracy and for isolating subtle relativistic signals.

The paper also surveys future prospects. The BepiColombo mission to Mercury, the JUICE mission to the Jovian system, and next‑generation laser ranging facilities promise sub‑centimeter ranging precision. Such data will tighten constraints on non‑Newtonian forces, possible dark‑matter clumps within the solar system, and higher‑order post‑Newtonian terms. The authors conclude that, while current ephemerides already confirm GR to remarkable precision, continued improvements in observational technology and dynamical modeling will keep solar‑system tests at the forefront of fundamental physics research.