Faster paleospin and deep-seated uncompensated mass as possible explanations for Ceres’ present-day shape and gravity

Mao, Xiaochen; McKinnon, William B.

doi:10.1016/j.icarus.2017.08.033

Cited by 21 publications

(30 citation statements)

References 32 publications

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“…As seen in Figure , the hydrostatic solutions from the gravity and shape are different for the present‐day rotation period. Mao and McKinnon () suggest that the gravity and topography can be both made hydrostatic at degree 2 and order 0 by changing the rotation period. In fact, the solution for the internal structure from gravity (

{\overset{J}{true}}_{2}

) and shape (

Ā_{20}

) are identical for a rotation period of 8.46 h. The moment of inertia of such hydrostatic equilibrium model is smaller ( λ ≈0.353) than for the shape or gravity solutions given the present rotation rate implying stronger differentiation.…”

Section: Resultsmentioning

confidence: 99%

“…Mao and McKinnon () state that the faster rotation hydrostatic solution is applicable for modeling Ceres' internal structure if the fossil bulge is frozen in. In other words, Ceres' shape coefficient

Ā_{20}

and gravity coefficient

{\overset{J}{true}}_{2}

should not have appreciably changed since the despinning event, which likely happened early in cerean history.…”

Section: Resultsmentioning

confidence: 99%

“…Two regions with larger crustal thicknesses are centered near the equator at 45 ∘ E and 135 ∘ W. The magnitude of the crustal thickening in the two regions is different (Figure 10b) due to the nonzero COM-COF offset. Mao and McKinnon (2018) propose that the {n = 2, m = 0} anomaly (i.e., the difference between the gravity and shape hydrostatic solutions, see Figure 8) could be coupled to the {n = 2, m = 2} anomaly. Mao and McKinnon (2018) argue that a combination of despinning and a deep-seated density anomaly due to low order convection or upwelling can explain the observed degree 2 in gravity and topography.…”

Section: Degree 2 Anomalymentioning

confidence: 99%

“…Mao and McKinnon (2018) propose that the {n = 2, m = 0} anomaly (i.e., the difference between the gravity and shape hydrostatic solutions, see Figure 8) could be coupled to the {n = 2, m = 2} anomaly. Mao and McKinnon (2018) argue that a combination of despinning and a deep-seated density anomaly due to low order convection or upwelling can explain the observed degree 2 in gravity and topography. Figure 14 shows an isostatic anomaly from n = 3 to n = 16 for four regions of interest.…”

Section: Degree 2 Anomalymentioning

confidence: 99%

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Constraints on Ceres' Internal Structure and Evolution From Its Shape and Gravity Measured by the Dawn Spacecraft

et al. 2017

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Ceres is the largest body in the asteroid belt with a radius of approximately 470 km. In part due to its large mass, Ceres more closely approaches hydrostatic equilibrium than major asteroids. Pre‐Dawn mission shape observations of Ceres revealed a shape consistent with a hydrostatic ellipsoid of revolution. The Dawn spacecraft Framing Camera has been imaging Ceres since March 2015, which has led to high‐resolution shape models of the dwarf planet, while the gravity field has been globally determined to a spherical harmonic degree 14 (equivalent to a spatial wavelength of 211 km) and locally to 18 (a wavelength of 164 km). We use these shape and gravity models to constrain Ceres' internal structure. We find a negative correlation and admittance between topography and gravity at degree 2 and order 2. Low admittances between spherical harmonic degrees 3 and 16 are well explained by Airy isostatic compensation mechanism. Different models of isostasy give crustal densities between 1,200 and 1,400 kg/m3 with our preferred model giving a crustal density of 1,287+70−87 kg/m3. The mantle density is constrained to be 2,434+5−8 kg/m3. We compute isostatic gravity anomaly and find evidence for mascon‐like structures in the two biggest basins. The topographic power spectrum of Ceres and its latitude dependence suggest that viscous relaxation occurred at the long wavelengths (>246 km). Our density constraints combined with finite element modeling of viscous relaxation suggests that the rheology and density of the shallow surface are most consistent with a rock, ice, salt and clathrate mixture.

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{\overset{J}{true}}_{2}

) and shape (

Ā_{20}

Section: Resultsmentioning

confidence: 99%

Ā_{20}

and gravity coefficient

{\overset{J}{true}}_{2}

should not have appreciably changed since the despinning event, which likely happened early in cerean history.…”

Section: Resultsmentioning

confidence: 99%

Section: Degree 2 Anomalymentioning

confidence: 99%

Section: Degree 2 Anomalymentioning

confidence: 99%

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Constraints on Ceres' Internal Structure and Evolution From Its Shape and Gravity Measured by the Dawn Spacecraft

et al. 2017

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“…In figure 20, we see the diffusion for the precession constants computed with a rotation rate that is 7% higher (Mao & McKinnon 2018), as discussed in section 3.2.4. If the early Ceres were in hydrostatic equilibrium, as supposed by Mao & McKinnon (2018), it could be in resonance with the frequencies s 1 ≈ −5.61 /yr, s C + 2(g C − g 6 ) + (g 5 − g 7 ) ≈ −6.07 /yr and s C + (3g C − 4g 6 + g 7 ) ≈ −6.39 /yr, which have weak effects on the obliquity as seen in figure 20 and the amplitudes of the oscillations of the obliquity would be similar. The events or phenomena, which would have changed its rotation rate, would not In (c) the rectangle A represents the precession constants for C ∈ [0.380 : 0.406] with a vertical red line for C = 0.393.…”

Section: Ceresmentioning

confidence: 80%

Long-term orbital and rotational motions of Ceres and Vesta

Vaillant

Laskar

Rambaux

2019

A&A

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Context. The dwarf planet Ceres and the asteroid Vesta have been studied by the Dawn space mission. They are the two heaviest bodies of the main asteroid belt and have different characteristics. Notably, Vesta appears to be dry and inactive with two large basins at its south pole. Ceres is an ice-rich body with signs of cryovolcanic activity. Aims. The aim of this paper is to determine the obliquity variations of Ceres and Vesta and to study their rotational stability. Methods. The orbital and rotational motions have been integrated by symplectic integration. The rotational stability has been studied by integrating secular equations and by computing the diffusion of the precession frequency.Results. The obliquity variations of Ceres over [−20 : 0] Myr are between 2 and 20 • and the obliquity variations of Vesta are between 21 and 45 • . The two giant impacts suffered by Vesta modified the precession constant and could have put Vesta closer to the resonance with the orbital frequency 2s 6 − s V . Given the uncertainty on the polar moment of inertia, the present Vesta could be in this resonance where the obliquity variations can vary between 17 and 48 • . Conclusions. Although Ceres and Vesta have precession frequencies close to the secular orbital frequencies of the inner planets, their long-term rotations are relatively stable. The perturbations of Jupiter and Saturn dominate the secular orbital dynamics of Ceres and Vesta and the perturbations of the inner planets are much weaker. The secular resonances with the inner planets also have smaller widths and do not overlap, contrary to the case of the inner planets.

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Compositions and Interior Structures of the Large Moons of Uranus and Implications for Future Spacecraft Observations

Castillo‐Rogez

Weiss

Beddingfield

et al. 2022

Preprint

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The five large moons of Uranus are important targets for future spacecraft missions. To motivate and inform the exploration of these moons, we model their internal evolution, present-day physical structures, and geochemical and geophysical signatures that may be measured by spacecraft. We predict that if the moons preserved liquid until present, it is likely in the form of residual oceans less than 30 km thick in Ariel, Umbriel, Titania, and Oberon. The preservation of liquid strongly depends on material properties and, potentially, on dynamical circumstances that are unknown. Miranda is unlikely to preserve liquid until present unless it experienced tidal heating a few tens of million years ago. The triaxial shapes estimated from Voyager 2 data for Miranda and Ariel further support the prospect that these moons are internally differentiated with a rocky core and icy shell. We find that since the thin residual layers may be hypersaline, their induced magnetic fields could be detectable by future spacecraft-based magnetometers. However, if the ocean is maintained primarily by ammonia, and thus well below the water freezing point, then its electrical conductivity may be too small to be detectable by spacecraft. Lastly, our calculated tidal Love number (k 2 ) and dissipation factor (Q) are consistent with the Q/k 2 values previously inferred from dynamical evolution models. In particular, we find that the low Q/k 2 estimated for Titania supports the hypothesis that Titania currently holds an ocean.

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Faster paleospin and deep-seated uncompensated mass as possible explanations for Ceres’ present-day shape and gravity

Cited by 21 publications

References 32 publications

Constraints on Ceres' Internal Structure and Evolution From Its Shape and Gravity Measured by the Dawn Spacecraft

Constraints on Ceres' Internal Structure and Evolution From Its Shape and Gravity Measured by the Dawn Spacecraft

Long-term orbital and rotational motions of Ceres and Vesta

Compositions and Interior Structures of the Large Moons of Uranus and Implications for Future Spacecraft Observations

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