Simple models of error spectra for planetary gravitational potentials as obtained from a variety of measurement configurations

Bills, B. G.; Ermakov, A.

doi:10.1016/j.pss.2019.104744

Cited by 8 publications

(3 citation statements)

References 20 publications

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“…To access the accuracy of admittance recovery, two items are needed. First, one needs to estimate the accuracy of the gravity coefficients determination, which can be done either with a simplified approach of Bills & Ermakov (2019) or with a full mission simulation using covariance analysis. Second, a global shape model or, at least, an estimate of the shape power spectrum is required.…”

Section: Sensitivity Of Future Gravity and Shape Data To The Icy Shel...mentioning

confidence: 99%

Probing the Icy Shell Structure of Ocean Worlds with Gravity–Topography Admittance

2022

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The structure of the icy shells of ocean worlds is important for understanding the stability of their underlying oceans as it controls the rate at which heat can be transported outward and radiated to space. Future spacecraft exploration of the ocean worlds (e.g., by NASA’s Europa Clipper mission) will allow for higher-resolution measurements of gravity and shape than currently available. In this paper, we study the sensitivity of gravity–topography admittance to the structure of icy shells in preparation for future data analysis. An analytical viscous relaxation model is used to predict admittance spectra given different shell structures determined by the temperature-dependent viscosity of a tidally heated, conductive shell. We apply these methods to the ocean worlds of Europa and Enceladus. We find that admittance is sensitive to the mechanisms of topography support at different wavelengths and estimate the required gravity performance to resolve transitions between these mechanisms. We find that measuring admittance would be complementary to ice-penetrating radar in constraining shell thickness as it would cover the cases for which a direct ice–ocean interface detection is less favorable with radar, i.e., for warmer and thicker shells. Finally, we find that admittance may be used to constrain the tidal dissipation within the icy shell, which would be complementary to a more demanding measurement of the tidal phase lag.

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Section: Sensitivity Of Future Gravity and Shape Data To The Icy Shel...mentioning

confidence: 99%

Probing the Icy Shell Structure of Ocean Worlds with Gravity–Topography Admittance

2022

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“…The superiority of gradiometry over RS in recovering the finer harmonics was hypothesised in [70], who derive analytical expressions to compare the error spectra of both methods. These rest on a number of simplifying assumptions, yet they serve to illustrate the scaling of formal errors as a function of harmonic degree n:…”

Section: Gradiometrymentioning

confidence: 99%

Cold Atom Interferometry for Enhancing the Radio Science Gravity Experiment: A Phobos Case Study

Plumaris

Dirkx²,

Siemes³

et al. 2022

Remote Sensing

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Interplanetary missions have typically relied on Radio Science (RS) to recover gravity fields by detecting their signatures on the spacecraft trajectory. The weak gravitational fields of small bodies, coupled with the prominent influence of confounding accelerations, hinder the efficacy of this method. Meanwhile, quantum sensors based on Cold Atom Interferometry (CAI) have demonstrated absolute measurements with inherent stability and repeatability, reaching the utmost accuracy in microgravity. This work addresses the potential of CAI-based Gradiometry (CG) as a means to strengthen the RS gravity experiment for small-body missions. Phobos represents an ideal science case as astronomic observations and recent flybys have conferred enough information to define a robust orbiting strategy, whilst promoting studies linking its geodetic observables to its origin. A covariance analysis was adopted to evaluate the contribution of RS and CG in the gravity field solution, for a coupled Phobos-spacecraft state estimation incorporating one week of data. The favourable observational geometry and the small characteristic period of the gravity signal add to the competitiveness of Doppler observables. Provided that empirical accelerations can be modelled below the nm/s2 level, RS is able to infer the 6 × 6 spherical harmonic spectrum to an accuracy of 0.1–1% with respect to the homogeneous interior values. If this correlates to a density anomaly beneath the Stickney crater, RS would suffice to constrain Phobos’ origin. Yet, in event of a rubble pile or icy moon interior (or a combination thereof) CG remains imperative, enabling an accuracy below 0.1% for most of the 10 × 10 spectrum. Nevertheless, technological advancements will be needed to alleviate the current logistical challenges associated with CG operation. This work also reflects on the sensitivity of the candidate orbits with regard to dynamical model uncertainties, which are common in small-body environments. This brings confidence in the applicability of the identified geodetic estimation strategy for missions targeting other moons, particularly those of the giant planets, which are targets for robotic exploration in the coming decades.

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“…To access the accuracy of admittance recovery two items are needed. First, one needs to estimate the accuracy of gravity coefficients determination, which can be done either with a simplified approach of Bills & Ermakov (2019) or with a full mission simulation using covariance analysis. Second, a global shape model or, at least, an estimate of the shape power spectrum is required.…”

Section: Sensitivity Of Future Gravity and Shape Data To The Icy Shel...mentioning

confidence: 99%

Probing the icy shell structure of ocean worlds with gravity-topography admittance

Akiba,

Ermakov,

Militzer

2021

Preprint

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The structure of the icy shells of ocean worlds is important for understanding the stability of their underlying oceans as it controls the rate at which heat can be transported outward and radiated to space. Future spacecraft exploration of the ocean worlds (e.g., by NASA's Europa Clipper mission) will allow for higher-resolution measurements of gravity and shape than currently available.In this paper, we study the sensitivity of gravity-topography admittance to the structure of icy shells in preparation for future data analysis. An analytical viscous relaxation model is used to predict admittance spectra given different shell structures determined by the temperature-dependent viscosity of a tidally heated, conductive shell. We apply these methods to the ocean worlds of Europa and Enceladus. We find that admittance is sensitive to the mechanisms of topography support at different wavelengths and estimate the required gravity performance to resolve transitions between these mechanisms. We find that the Airy isostatic model is unable to accurately describe admittance universally across all wavelengths when the shell thickness is a significant fraction of body's radius. Our models suggest that measurements of admittance at low spherical harmonic degrees are more sensitive to thick shells with high tidal dissipation, and may complement ice-penetrating radar measurements in constraining shell thickness. Finally, we find that admittance may be used to constrain the tidal dissipation within the icy shell, which would be complementary to a more demanding measurement of the tidal phase lag.

show abstract

Simple models of error spectra for planetary gravitational potentials as obtained from a variety of measurement configurations

Cited by 8 publications

References 20 publications

Probing the Icy Shell Structure of Ocean Worlds with Gravity–Topography Admittance

Probing the Icy Shell Structure of Ocean Worlds with Gravity–Topography Admittance

Cold Atom Interferometry for Enhancing the Radio Science Gravity Experiment: A Phobos Case Study

Probing the icy shell structure of ocean worlds with gravity-topography admittance

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