Mars without Tharsis

Zuber, M. T.; Smith, David E.

doi:10.1029/97je02527

Cited by 56 publications

(75 citation statements)

References 53 publications

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“…On Mars, the excess degree-2 power can be explained by Tharsis. To demonstrate this, we removed Tharsis according to the methods of Zuber and Smith (1997) 36 . We find that the degree-2 observed/extrapolated power ratio for Mars is reduced to 0.23 and 0.48 for topography and gravity, respectively, when Tharsis is removed.…”

Section: Methodsmentioning

confidence: 99%

The tidal–rotational shape of the Moon and evidence for polar wander

Garrick‐Bethell

Perera

Nimmo

et al. 2014

Nature

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Summary paragraph: The origin of the Moon's large-scale topography is important for understanding lunar geology 1 , lunar orbital evolution 2 , and the Moon's orientation in the sky 3 .Previous hypotheses for its origin have included late accretion events 4 , large impacts 5 , tidal effects 6 , and convection processes 7 . However, testing these hypotheses and quantifying the Moon's topography is complicated by the large basins that have formed since the crust crystallized. Here we estimate the low-order lunar topography and gravity spherical harmonics outside these basins and show that the bulk of the degree-2 topography is consistent with a crustbuilding process controlled by early tidal heating throughout the Moon. The remainder of the degree-2 topography is consistent with a frozen tidal-rotational bulge that formed later, at a semimajor axis of 32 Earth radii. The probability of the degree-2 shape having these two separate tidal characteristics by chance is less than 1%. We also infer that internal density contrasts eventually reoriented the Moon's polar axis 36  4°, to the present configuration we observe today. Together, these results link the geology of the near and far sides, and resolve longstanding questions about the Moon's low-order shape, gravity, and history of polar wander. 2 Main TextThe theory of equilibrium figures of rotating fluid bodies is a classic problem in geophysics, and it has been helpful in understanding the shapes of the Sun and planets. However, the origin for the Moon's shape has remained an open problem in the last century 2,6,[8][9][10] , and the body's deviations from any simple tidal-rotational (spherical harmonic degree-2) figure are large 11 . This difficulty is surprising given the Moon's presumably simple early thermal history: born hot and quickly cooled, one might expect the Moon to be described by a simple figure of equilibrium.Researchers have traditionally suggested that the Moon's degree-2 spherical harmonic gravity coefficients, which have been used as proxies for the degree-2 shape, are especially large when compared to higher degree coefficients 9,12 . Figure 1 shows a power law or "Kaula's rule" fit to degrees n = 3 to 50 for the Moon's gravity 13 and topography data 14 . The power at degree 2 is 4.5 times and 2.6 times the power expected from extrapolating the best-fit power law, for gravity and topography, respectively, supporting the idea that the degree-2 coefficients are unique. Indeed, the fraction of excess power for topography is greater than the excesses for Venus, Earth, and Mars (SI). Authors have tried to interpret the Moon's strong degree-2 power as a frozen tidalrotational state inherited from when the Moon was closer to the Earth, known as the fossil bulge hypothesis 6 . An open problem, however, has been that the ratio of the C 2,0 and C 2,2 spherical harmonic coefficients is different from the expected value by a factor of 2. 6 (refs. 2,10).Adding to the fossil bulge idea and motivated by tidal processes in Europa's ice shell 15 , GarrickBet...

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Section: Methodsmentioning

confidence: 99%

The tidal–rotational shape of the Moon and evidence for polar wander

Garrick‐Bethell

Perera

Nimmo

et al. 2014

Nature

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“…extrapolation of the higher-degree terms. This low-degree signal is likely a consequence of the lithospheric load and deflection associated with the Tharsis province (see Phillips et al, 2001;Zuber and Smith, 1997). The error spectrum of the geoid is seen to be larger than the signal for degrees greater than $100.…”

Section: Spectral Analysismentioning

confidence: 95%

“…For instance, most planets and satellites possess significant rotational and/or tidal contributions to their degree-2 shape, and these signatures can be minimized by setting these coefficients to zero. For Mars, in addition to the degree-2 rotational signature, the longest wavelength components have been affected by the load and flexural response associated with the Tharsis province (see Phillips et al, 2001;Wieczorek and Zuber, 2004;Zuber and Smith, 1997).…”

Section: Spatial Domainmentioning

confidence: 99%

Gravity and Topography of the Terrestrial Planets

Wieczorek¹

2015

Treatise on Geophysics

134

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“…The most widely accepted version of that analysis held that the nonhydrostatic component of the degree 2 gravity field is symmetric about an equatorial axis through Tharsis [Reasenberg, 1977;Kaula, 1979;Kaula et al, 1989; Zubet and Smith, 1997]. On the other hand, Bills [1989a,b] of long-term elastic strength within Earth in stabilizing its rotation should also be critically reviewed.…”

Section: Paper Number 1998je900003mentioning

confidence: 99%