Vertical structures induced by embedded moonlets in Saturn’s rings

Hoffmann, H.; Seiß, M.; Salo, H.; Spahn, F.

doi:10.1016/j.icarus.2015.02.003

Cited by 33 publications

(9 citation statements)

References 46 publications

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“…Once every half Saturn year the ring plane aligns with the center of the Sun, and for a brief time the northern and southern sides of the rings receive essentially no sunlight. During equinox in August 2009, when the Sun was edge-on to the rings, vertically extended objects cast shadows across the rings (17). During this period, Cassini observed shadows up to 2.5 km long (Fig.…”

Section: Ringsmentioning

confidence: 96%

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Cassini-Huygens’ exploration of the Saturn system: 13 years of discovery

Spilker

2019

Science

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The Cassini-Huygens mission to Saturn provided a close-up study of the gas giant planet, as well as its rings, moons, and magnetosphere. The Cassini spacecraft arrived at Saturn in 2004, dropped the Huygens probe to study the atmosphere and surface of Saturn’s planet-sized moon Titan, and orbited Saturn for the next 13 years. In 2017, when it was running low on fuel, Cassini was intentionally vaporized in Saturn’s atmosphere to protect the ocean moons, Enceladus and Titan, where it had discovered habitats potentially suitable for life. Mission findings include Enceladus’ south polar geysers, the source of Saturn’s E ring; Titan’s methane cycle, including rain that creates hydrocarbon lakes; dynamic rings containing ice, silicates, and organics; and Saturn’s differential rotation. This Review discusses highlights of Cassini’s investigations, including the mission’s final year.

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Section: Ringsmentioning

confidence: 96%

“…Other findings include three-dimensional structures in the planet's dynamic rings (17), a giant Saturn storm that completely encircled a northern latitude band for almost a year (18), a longlived hexagonal jet stream encircling the north pole (19), and evidence that the captured moon Phoebe may have originated in the outer Solar System's Kuiper Belt (20).…”

mentioning

confidence: 99%

Cassini-Huygens’ exploration of the Saturn system: 13 years of discovery

Spilker

2019

Science

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“…Therefore, the inner gap -due to the higher angular speed of the ring material -overtakes the embedded moonlet while the outer one falls behind. Viscous diffusion of the ring material counteracts this gravitational scattering process and thus results in a closing of the opened gap with growing azimuthal distance to the embedded moonlet (Spahn and Sremčević 2000;Sremčević et al 2002;Seiß et al 2005;Hoffmann et al 2015). For moonlets larger than a critical radius, its gravity compensates the viscous diffusion along the whole circumference of the orbit and thus the gap is kept open.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic Simulations of Asymmetric Propeller Structures in Saturn's Rings

Seiler

Seiß

Hoffmann

et al. 2019

ApJS

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The observation of the non-Keplerian behavior of propeller structures in Saturn's outer A ring (Tiscareno et al. 2010;Seiler et al. 2017;Spahn et al. 2018) raises the question, how the propeller responds to the wandering of the central embedded moonlet. Here, we study numerically how the induced propeller is changing for a librating moonlet. It turns out, that the libration of the moonlet induces an asymmetry in the structural imprint of the propeller, where the asymmetry is depending on the moonlet's libration period and amplitude. Further, we study the dependence of the asymmetry on the libration period and amplitude for a moonlet with 400 m Hill radius, which is located in the outer A ring. In this way, we are able to apply our findings to the largest found propeller structures -such as Blériot -which are expected to be of similar size. For Blériot, we can conclude that, supposed the moonlet is librating with the largest observed period of 11.1 years and an azimuthal amplitude of about 1845 km Spahn et al. 2018), a small assymetry should be measurable but depends on the moonlet's libration phase at the observation time. The excess motions of the other giant propellers -such as Santos Dumont and Earhart -have similar amplitudes as Blériot and thus might allow the observation of larger asymmetries due to their smaller azimuthal extent. This would permit to scan the whole gap structure for asymmetries.Although the librational model of the moonlet is a simplification, our results are a first step towards the development of a consistent model for the description of the formation of asymmetric propellers caused by a freely moving moonlet.

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“…Sremčević et al (2002) presented an analytical solution for the gap density profile. An extension of the model to the vertical degree of freedom was developed by Hoffmann et al (2013Hoffmann et al ( , 2015, which explained the shape of the shadow cast by the propeller Earhart on the rings in Cassini ISS images taken close to Saturn's vernal equinox in August 2009. Seiß et al (2005) were the first to employ N-body simulations in order to investigate a moonlet-induced propeller structure.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic Simulations of Moonlet-induced Propellers in Saturn’s Rings: Application to Blériot

Seiß

Albers

Sremčević

et al. 2018

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One of the biggest successes of the Cassini mission is the detection of small moons (moonlets) embedded in Saturns rings which cause S-shaped density structures in their close vicinity, called propellers (Spahn & Sremčević 2000;Tiscareno et al. 2006;Sremčević et al. 2007). Here, we present isothermal hydrodynamic simulations of moonlet-induced propellers in Saturn's A ring which denote a further development of the original model (Spahn & Sremčević 2000). We find excellent agreement between these new hydrodynamic and corresponding N-body simulations. Furthermore, the hydrodynamic simulations confirm the predicted scaling laws (Spahn & Sremčević 2000) and the analytical solution for the density in the propeller gaps (Sremčević et al. 2002). Finally, this mean field approach allows us to simulate the pattern of the giant propeller Blériot, which is too large to be modeled by direct N-body simulations. Our results are compared to two stellar occultation observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS), that intersect the propeller Blériot. Best fits to the UVIS optical depth profiles are achieved for a Hill radius of 590 m, which implies a moonlet diameter of about 860 m. Furthermore, the model favours a kinematic shear viscosity of the surrounding ring material of ν 0 = 340 cm 2 s −1 , a dispersion velocity in the range of 0.3 cm s −1 < c 0 < 1.5 cm s −1 , and a fairly high bulk viscosity 7 < ξ 0 /ν 0 < 17. These large transport values might be overestimated by our isothermal ring model and should be reviewed by an extended model including thermal fluctuations.

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Vertical structures induced by embedded moonlets in Saturn’s rings

Cited by 33 publications

References 46 publications

Cassini-Huygens’ exploration of the Saturn system: 13 years of discovery

Cassini-Huygens’ exploration of the Saturn system: 13 years of discovery

Hydrodynamic Simulations of Asymmetric Propeller Structures in Saturn's Rings

Hydrodynamic Simulations of Moonlet-induced Propellers in Saturn’s Rings: Application to Blériot

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