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. 2018 Jan 18;9(1):289.
doi: 10.1038/s41467-017-02558-1.

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

Antonio Genova  1   2 , Erwan Mazarico  3 , Sander Goossens  3   4 , Frank G Lemoine  3 , Gregory A Neumann  3 , David E Smith  5 , Maria T Zuber  5
Affiliations

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

Antonio Genova et al. Nat Commun. .

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, [Formula: see text] = (2.246 ± 0.022) × 10-7. Finally, we obtain an estimate of the time variation of the Sun gravitational parameter, [Formula: see text] = (-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 [Formula: see text] to be <4 × 10-14 per year.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Fig. 1
Fig. 1
Noise level of the MESSENGER range data. RMS of range measurements as a function of the Sun–Probe–Earth angle, which illustrates the effect of the solar plasma on the data noise. Lower SPE angles produce higher noise since the signal passes through dense solar plasma closer to the Sun. The data collected near superior solar conjunction (SPE < 35°) were not included in the analysis. The figure also shows the antennas that were used to provide the downlink to the DSN station. The range data were always collected during tracking passes with fanbeam for uplink and PPAs for downlink reducing thermal noise effects
Fig. 2
Fig. 2
Data distribution throughout Mercury’s orbit. Number of the analyzed measurements as function of the Mercury distance from the Sun in AU. Colors indicate the noise level distribution during each phase bin of Mercury’s orbit. The greater part of the data was collected close to Mercury’s perihelion and aphelion
Fig. 3
Fig. 3
Temporal distribution of the range biases with three Mercury’s ephemeris. The measurement biases are required to fit the MESSENGER range data at the noise level with the JPL DE430 (purple) and D432 (blue) ephemerides, and our integrated trajectory for Mercury (black). These biases were used to determine the quality of the ephemeris results. After convergence of the global solution, all the adjusted parameters (Methods) are applied in a final iteration, in which the range biases are adjusted instead of the Mercury’s initial state, GM⊙, J2⊙, β, η, and GM⊙°∕GM⊙. Large range biases suggest significant errors in the planet’s ephemeris
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