Mars without the equilibrium rotational figure, Tharsis, and the remnant rotational figure

Abstract

[1] We use a revised partitioning of the planet figure into equilibrium and nonequilibrium contributions that takes into account the presence of an elastic lithosphere to study the Martian gravity field and shape. The equilibrium contribution is associated with the present rotational figure, and the nonequilibrium contribution is dominated by Tharsis and a remnant rotational figure supported by the elastic lithosphere that traces the paleopole location prior to the formation of Tharsis. We calculate the probability density functions for Tharsis' size and location, the paleopole location, and the global average thickness of the elastic lithosphere at the time Tharsis was emplaced. Given the observed degree-3 spherical harmonic gravity coefficients, the expected Tharsis center location is 258.6 ± 4.2°E, 9.8 ± 0.9°N, where the uncertainties represent the 90% confidence interval. Given this Tharsis center location and the observed degree-2 spherical harmonic gravity coefficients, the expected paleopole location prior to the emplacement of Tharsis is 259.5 ± 49.5°E, 71.1 −14.4 +17.5°N , and the expected elastic lithospheric thickness at the time of loading is 58 −32 +34 km. Our estimated paleopole colatitude implies 18.9 −17.5 +14.4°o f true polar wander (TPW) driven by the emplacement of Tharsis, in disagreement with previous studies that invoke large TPW. The remnant rotational figure is visible in both the nonequilibrium degree-2 geoid (areoid) without Tharsis and the nonequilibrium degree-2 topography without Tharsis. The remnant rotational figure is also visible in the total nonequilibrium geoid without Tharsis, but it is not visible in the total nonequilibrium topography without Tharsis due to the strong signal of the north-south dichotomy. Shorter wavelength geological features become significantly more visible in the geoid with the removal of the long wavelength contributions of the equilibrium rotational figure, Tharsis, and the remnant rotational figure. Removal of the equilibrium rotational figure and Tharsis from the topography reveals a better defined north-south dichotomy boundary.Citation: Matsuyama, I., and M. Manga (2010), Mars without the equilibrium rotational figure, Tharsis, and the remnant rotational figure,

Long-term polar motion on a quasi-fluid planetary body with an elastic lithosphere: Semi-analytic solutions of the time-dependent equation

“…The most typical application would be Mars' TPW (e.g., Melosh, 1980;Schultz and Lutz-Garihan, 1981;Schultz and Lutz, 1988). The theory mentioned above enables us to understand dynamics and evolution of Mars' system including both its interior sub-systems (e.g., Daradich et al, 2008;Matsuyama and Manga, 2010) and surface sub-systems (e.g., Perron et al, 2007;Kite et al, 2009). These may be related to large volcanic provinces (e.g., Zhong, 2009) or polar layered deposits (e.g., Watters et al, 2007).…”

Rotation of the Terrestrial Planets

“…Nevertheless, the terrestrial planets most likely all have had periods of large polar wander when the solid surface of the planet reorients with respect to the rotation axis as a result of mass redistribution due to internal or external causes that drives the planet to a new state of minimum energy corresponding to principal axis rotation (Gold, 1955;Matsuyama et al, 2006;Willemann, 1984). For example, large polar wander of a few 10 is thought to be caused by the emplacement of Tharsis (Matsuyama and Manga, 2010; see also Zhong, 2009). …”

Mars: a small terrestrial planet

“…This period is characterized by the formation and evolution of a secondary atmosphere as the results of a complex interplay between non-thermal escape processes, volcanic degassing, impact processes, and surface precipitation of volatiles-bearing phases. Mass transfer associated with internal movement, tectonic, or volcanic activities has affected the inertia tensor of Mars throughout its interior history, and has likely induced several episodes of True Polar Wander resulting in profound modification of local surface conditions, topography (Perron et al 2007;Matsuyama and Manga 2010) climate, and the stability of surface-ice or water reservoirs (Kite et al 2009;Bouley et al 2016). The present 6 mbars atmosphere may have been influenced by prolonged volcanic activity and CO 2 release during the Amazonian (Gillmann et al 2011), though such calculations are hampered by limited constraints on the concentration of volatiles in martian basalts (Filiberto et al 2016).…”