Abstract:

We present the new INPOP17a[1] planetary and lunar ephemeris, which includes improvements for the planet orbits as well as the lunar interior structure. From the improvements in the lunar interior structure and the refinements to the data reduction, the LLR residuals obtained with INPOP17a range between 1.4 – 1.8 cm for the recent and most accurate data. The LLR reduction model follows IERS 2010 recommendations[2]. For the Grasse station a seasonal signal is removed with the effect identified as hydrology loading, with the help of a multi-geodetic characterization[3] confirmed with available hydrology models. Thanks to these refinements and the availability of new accurate IR LLR data from Grasse station[4], we were able to perform fundamental tests of the principle of equivalence[5] as well as identify and characterize inconsistencies[6] existing between the LLR estimated degree-3 spherical harmonics for the Moon and that obtained through the gravity field recovered from the GRAIL mission[7]. A work is in progress to identify the causation of the inconsistency, likely to be linked to the lunar interior structure model.

References:

1. Viswanathan, V., Fienga, A., Gastineau, M. & Laskar, J. INPOP17a planetary ephemerides. Notes Sci. Tech. l'Institut Mec. Celeste 108, (2017).

2. Petit, G. & Luzum, B. IERS Conventions (2010). IERS Tech. Note 36, (2010).

3. Mémin, A. et al. Multi-geodetic characterization of the seasonal signal at the CERGA geodetic reference station, France. in EGU General Assembly Conference Abstracts 19, 7450 (2017).

4. Courde, C. et al. Lunar laser ranging in infrared at the Grasse laser station. Astron. Astrophys. 602, A90 (2017).

5. Viswanathan, V. et al. The new lunar ephemeris INPOP17a and its application to fundamental physics. Mon. Not. R. Astron. Soc. 476, 1877–1888 (2018).

6. Viswanathan, V. Improving the dynamical model of the Moon using lunar laser ranging and spacecraft data. (Ph.D Thesis, Observatoire de Paris, 2017).

7. Konopliv, A. S. et al. The JPL lunar gravity field to spherical harmonic degree 660 from the GRAIL Primary Mission. J. Geophys. Res. Planets 118, 1415–1434 (2013).

Acknowledgement:

V.V acknowledges the financial support of Labex-ESEP Postdoctoral grant for continuing this research. The LLR reduction model was implemented in CNES POD software – GINS.