Fluid Core Size of Mars from Detection of the Solar Tide

Abstract

The solar tidal deformation of Mars, measured by its k 2 potential Love number, has been obtained from an analysis of Mars Global Surveyor radio tracking. The observed k 2 of 0.153 ± 0.017 is large enough to rule out a solid iron core and so indicates that at least the outer part of the core is liquid. The inferred core radius is between 1520 and 1840 kilometers and is independent of many interior properties, although partial melt of the mantle is one factor that could reduce core size. Ice-cap mass changes can be deduced from the seasonal variations in air pressure and the odd gravity harmonic J 3 , given knowledge of cap mass distribution with latitude. The south cap seasonal mass change is about 30 to 40% larger than that of the north cap.

The thermal evolution of Mars as constrained by paleo-heat flows

“…Our results are consistent with several independent geophysical and geological observations. For example, high mantle tempera tures reduce core cooling, possibly contributing to the present day existence of a, at least partly, fluid core (deduced from the response to the solar tide; Yoder et al, 2003), and to the simulta neous absence of an endogenic magnetic field (e.g., Acufia et al, 2001) due to the reduction (or even suppression) of core convec tion (e.g., Nimmo and Stevenson, 2000). Our results are also consis tent with a lower amount of global contraction since the Early Noachian than expected from thermal history models, as deduced from thrust faults recorded on the surface (Nahm and Schultz, 2011); indeed, the lack of mantle cooling (and maybe mantle heat ing) limits the thermal contraction that can drive surface contrac tion.…”

Seismological implications of a lithospheric low seismic velocity zone in Mars

“…The Love number k 2 inferred from solar tides indicates the existence of at least an outer liquid 111 core (Yoder et al, 2003). Whether Mars has a solid inner-core or not is uncertain.…”

“…In our model, we do not include a solid inner core. A range of core radii is permitted when 114 modeling the tidal k 2 and moment of inertia (Yoder et al, 2003); we adopt a baseline value of 1650 115 km similar to that employed by Nimmo and Faul (2013). To study the mantle LVZ, the exact radius is 116 not critical.…”

Melting of the Martian mantle from 1.0 to 4.5 GPa

“…Therefore, if the actual Martian mantle is similar in composition to that of DWM, the Adirondack basalts can be explained as a melt that experienced a small amount of crystal fractionation in the shallower Martian mantle (Filiberto et al, 2008). As mentioned in the Introduction, resent estimations have suggested that the Martian mantle may actually have a higher Mg# (0.77 -0.80) than that of DWM (0.75) (e.g., Yoder et al, 2003;Agee and Draper, 2004;Musselwhite et al, 2006;Minitti et al, 2007); however, its actual values remain uncertain. We consider the influence of Mg# on the primary partial melt composition.…”