A Libration Model for Enceladus Based on Geodetic Control Point  Network Analysis

Nadezhdina, I.; Zubarev, A. E.; Brusnikin, E.S.; Oberst, J.

doi:10.5194/isprs-archives-xli-b4-459-2016

Cited by 7 publications

(10 citation statements)

References 6 publications

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“…Degree 2 gravity, however, predicts a thinner shell (in agreement with librations) if C 22 is 2𝜎 higher than its SOL1 central value, as suggested by the alternative gravity solution SOL2 (Table S2). Alternatively, the degree 2 shape could be responsible for the disagreement: while the new ellipsoidal shape of Thomas et al [2016] does not affect much the results (Table S6), the recent ellipsoidal shape of Nadezhdina et al [2016] predicts more degree 2 compensation and thus a thinner shell. Second, we did not allow for a lot of surface porosity in our three-layer model, but we can easily do it with a four-layer model.…”

Section: Discussionmentioning

confidence: 99%

“…TOPB is less flattened than TOPA and its coefficient H 22 follows the geoid (see Table S.4). The new ellipsoidal shape of Nadezhdina et al [2016] has a polar flattening (−3H 20 /2R) close to the one of TOPA but its equatorial flattening (6H 22 /R) is nearly hydrostatic (similarly to TOPB).…”

Section: S3 Shape Data (Tables S4 and S5)mentioning

confidence: 91%

“…The shape of the mid-size Saturnian satellites has been determined by fitting an ellipsoid [Thomas et al, 2007[Thomas et al, , 2016Nadezhdina et al, 2016] and by directly estimating the spherical harmonic components of the topography [Nimmo et al, 2011]. For Enceladus and Dione, we use the shape of Nimmo et al [2011] (denoted TOPA), which provides all harmonic coefficients of degree two and three.…”

Section: S3 Shape Data (Tables S4 and S5)mentioning

confidence: 99%

“…These data reveal the presence of a hydrated silicate core with a radius of about three fourths of the surface radius, but the crust-ocean partition of the outer H 2 O layer has remained controversial. The recent measurement of Enceladus's librations [Thomas et al, 2016;Nadezhdina et al, 2016] demonstrates that the crust is a thin ice shell floating on a global ocean.…”

Section: Introductionmentioning

confidence: 99%

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Enceladus's and Dione's floating ice shells supported by minimum stress isostasy

Beuthe

Rivoldini

Trinh

2016

Geophysical Research Letters

152

182

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Enceladus's gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean, in contradiction of the thin shell implied by librations. Here we propose a new isostatic model minimizing crustal deviatoric stress and demonstrate that gravity and shape data predict a 38 ± 4 km thick ocean beneath a 23 ± 4 km thick shell agreeing with—but independent of—libration data. Isostatic and tidal stresses are comparable in magnitude. South polar crust is only 7 ± 4 km thick, facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration. Enceladus's resonant companion, Dione, is in a similar state of minimum stress isostasy. Its gravity and shape can be explained in terms of a 99 ± 23 km thick isostatic shell overlying a 65 ± 30 km thick global ocean, thus providing the first clear evidence for a present‐day ocean within Dione.

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Section: Discussionmentioning

confidence: 99%

Section: S3 Shape Data (Tables S4 and S5)mentioning

confidence: 91%

Section: S3 Shape Data (Tables S4 and S5)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Enceladus's and Dione's floating ice shells supported by minimum stress isostasy

Beuthe

Rivoldini

Trinh

2016

Geophysical Research Letters

152

182

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show abstract

“…With the arrival of Cassini in the Saturn system, new global control networks (Oberst et al, 2017) and global mosaics were completed (Roatsch et al, 2008(Roatsch et al, , 2013Zubarev et al, 2014; and see global color products by P. Schenk, e.g., Planetary Photojournal, https://photojournal.jpl.nasa.gov/catalog/PIA18435). Cassini-based control networks have now also been extensively utilized to evaluate Enceladus' rotation, including its libration (Giese et al, 2011;Nadezhdina et al, 2016;Thomas et al, 2016) and obliquity (Giese, 2014).…”

Section: 1029/2018ea000399mentioning

confidence: 99%

A New Enceladus Global Control Network, Image Mosaic, and Updated Pointing Kernels From Cassini's 13‐Year Mission

Bland

Becker

Edmundson

et al. 2018

Earth and Space Science

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NASA's Cassini spacecraft spent 13 years exploring the Saturn system, including 23 targeted flybys of the small, geologically active moon Enceladus. These flybys provided a wealth of image data from Cassini's Imaging Science Subsystem. To improve the usability of the Enceladus data set, we created a new, global photogrammetric control network for Enceladus that enabled compilation of a versatile cartographic package to support geologic mapping and other investigations. The network used 586 images in four image filters with a pixel scale generally between 50 and 500 m per pixel and a phase angle less than 120° and consisted of 10,362 tie points and 173,704 individual image measures, averaging nearly 17 measures per tie point. Least squares bundle adjustment resulted in a root‐mean‐square residual of 0.45 pixel, corresponding to root‐mean‐square ground point uncertainties of 66, 51, and 46 m in latitude, longitude, and radius, respectively. Using our geodetic control network, we created new global image mosaics, coregistered flyby mosaics to support geologic mapping, and updated pointing kernels for every image used in the solution. These products, including the updated pointing kernels, are available to the community through NASA's Planetary Data System Imaging Annex. The bundle adjustment solution also yielded independently determined shape information, resulting in radii within the stated uncertainty of International Astronomical Union values. The challenges of the data set, and the technical methodology described here are applicable to bodies imaged during multiple flybys with variable viewing and illumination geometry, including other midsized satellites of Saturn, and the Europa Clipper mission.

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Effects of Transient Obliquity Tides Within Mimas' Warm, Icy Interior Preserved as a Frozen Fossil Figure

Gyalay,

Nimmo,

Downey

2024

JGR Planets

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Mimas has a high eccentricity and an anomalously high physical libration like its neighbor, Enceladus, but does not appear to have a geologically active surface. We investigate Mimas' interior with a technique that infers spatial variations in tidal heating from its global shape. To account for its hydrostatic shape, we find Mimas' normalized moment of inertia is 0.375 ± 0.0025, indicating a relatively undifferentiated world. Its remaining topography is consistent with a ∼30 km thick conductive ice shell in Airy isostasy atop a weakly convecting ∼30 km thick layer that itself mantles a ∼140 km radius ice‐rock interior. The convective shell's density must be closer to the interior density to satisfy our moment of inertia and provide a denser compensating layer for Airy isostasy. This ice‐rock interior is elongated along the Mimas‐Saturn axis, which can match Mimas' observed physical libration without appealing to an ocean. The inferred ice shell thickness variations indicate a high obliquity (≈1.7°). We suggest that the obliquity damped rapidly, after which topography froze in when internal heat was conducted out of Mimas quicker than isostatic ice shell thickness variations could relax. We speculate on several possible explanations for this transient high obliquity, including excitation by ring‐forming material following the recent tidal disruption of an eccentric satellite. We cannot rule out a young Mimantean ocean, but our inferred moment of inertia favors a Mimas that was solid when it experienced a period of high obliquity, did not significantly melt during a recent resonance with Enceladus, and is solid today.

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A Libration Model for Enceladus Based on Geodetic Control Point Network Analysis

Cited by 7 publications

References 6 publications

Enceladus's and Dione's floating ice shells supported by minimum stress isostasy

Enceladus's and Dione's floating ice shells supported by minimum stress isostasy

A New Enceladus Global Control Network, Image Mosaic, and Updated Pointing Kernels From Cassini's 13‐Year Mission

Effects of Transient Obliquity Tides Within Mimas' Warm, Icy Interior Preserved as a Frozen Fossil Figure

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