Mercury and frame-dragging in light of the MESSENGER flybys: conflict with general relativity, poor knowledge of the physical properties of the Sun, data reduction artifact, or still insufficient observations?

Abstract

The Lense-Thirring precession of the longitude of perihelion of Mercury, as predicted by general relativity by using the value of the Sun's angular momentum S = 190 x 10^39 kg m^2 s^-1 from helioseismology, is -2.0 milliarcseconds per century, computed in a celestial equatorial reference frame. It disagrees at 4-{\sigma} level with the correction 0.4 +/- 0.6 milliarcseconds per century to the standard Newtonian/Einsteinian precession, provided that the latter is to be entirely attributed to frame-dragging. The supplementary precession was recently determined in a global fit with the INPOP10a ephemerides to a long planetary data record (1914-2010) including also 3 data points collected in 2008-2009 from the MESSENGER spacecraft. The INPOP10a models did not include the solar gravitomagnetic field at all, so that its signature might have partly been removed in the data reduction process. On the other hand, the Lense-Thirring precession may have been canceled to a certain extent by the competing precessions caused by small mismodeling in the quadrupole mass moment of the Sun and in the PPN parameter beta entering the Schwarzschild-like 1PN precession, both modeled in INPOP10a. On the contrary, the oblateness of Mercury itself has a negligible impact on its perihelion. The same holds for the mismodelled actions of both the largest individual asteroids and the ring of the minor asteroids. Future analysis of more observations from the currently ongoing MESSENGER mission will shed further light on such an issue which, if confirmed, might potentially challenge our present-day picture of the currently accepted laws of gravitation and/or of the physical properties of the Sun.