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Exploring the temporal variation of the solar quadrupole moment from relativistic gravitation contributions: A fortuitous circumstance?

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Exploring the temporal variation of the solar quadrupole moment from relativistic gravitation contributions: A

fortuitous circumstance?

J.P. Rozelot

a

, S. Eren

b

aUniversité Côte d’Azur, 77 Chemin des Basses Moulières, 06130 Grasse,France

bThe Arctic University of Norway, Department of Physics and Technology, Postboks 6050 Langnes, 9037 Tromsø, Norway

Received 29 June 2019; received in revised form 29 October 2019; accepted 31 October 2019. Available online 8 November 2019 Abstract

Due to its oblateness, the Sun carries a solar quadrupole moment playing a key role at the crossroad of fundamental solar physics, astrometry and celestial mechanics. There is nowadays a general agreement on its order of magnitude (≈ 2x10 -7), but its temporal dependence is still poorly known. Helioseismology led to a variation within the solar cycle by less than 0.04%, not yet confirmed by other means. Analysis of the perihelion precession of planetary orbits computed in the solar equatorial coordinate system, instead of the ecliptic coordinate system usually used, shows that a periodic variation of the J2 term rather than of a simple constant, must be considered. Gravity tests within the Planetary and Lunar Ephemerides provide a fruitful independent approach. Confronting results from three sets of Ephemerides computed at different periods of time, a variability dependence within the solar cycle can be evidenced. If this outcome is not fortuitous, such a finding suggests a quadratic fit, that can be explained through the variation of the rotation law with latitude and time.

Keywords: Sun: fundamental parameters; Sun: activity; Ephemerides

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