The lingering anomalous secular increase of the eccentricity of the orbit of the Moon: further attempts of explanation of cosmological origin

TL;DR

This paper investigates the persistent unexplained increase in the Moon's orbital eccentricity, testing cosmological explanations but finding them insufficient to account for the observed anomaly.

Contribution

It provides a refined analysis of lunar orbital data and evaluates cosmological models, concluding they cannot explain the anomaly.

Findings

Extended lunar data analysis confirms the anomaly persists.

Cosmological effects are too small to explain the eccentricity increase.

Standard models do not account for the observed rate of change.

Abstract

A new analysis of extended data records collected with the Lunar Laser Ranging (LLR) technique performed with improved tidal models was not able to resolve the issue of the anomalous rate $\dot e$ of the eccentricity $e$ of the orbit of the Moon, which is still in place with a magnitude of $\dot e=(5\pm 2)\times 10^{-12}$ yr$^{-1}$. Some possible cosmological explanations are offered in terms of the post-Newtonian effects of the cosmological expansion, and of the slow temporal variation of the relative acceleration rate $\ddot{S} S^{-1}$ of the cosmic scale factor $S$. None of them is successful since their predicted secular rates of the lunar eccentricity are too small by several orders of magnitude.