The Gravity Field and Interior Structure of Enceladus

Science ◽  
2014 ◽  
Vol 344 (6179) ◽  
pp. 78-80 ◽  
Author(s):  
L. Iess ◽  
D. J. Stevenson ◽  
M. Parisi ◽  
D. Hemingway ◽  
R. A. Jacobson ◽  
...  
Keyword(s):  
Gravity Field ◽  
Polar Region ◽  
Hydrostatic Equilibrium ◽  
The Body ◽  
Interior Structure ◽  
Negative Mass ◽  
Cassini Mission ◽  
Doppler Data ◽  
The Moment ◽  
South Polar

The small and active Saturnian moon Enceladus is one of the primary targets of the Cassini mission. We determined the quadrupole gravity field of Enceladus and its hemispherical asymmetry using Doppler data from three spacecraft flybys. Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (106J2= 5435.2 ± 34.9, 106C22= 1549.8 ± 15.6, 1σ) and their ratio (J2/C22= 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR2, whereMis the mass andRis the radius, suggesting a differentiated body with a low-density core.

scholarly journals Phoebe’s differentiated interior from refined shape analysis

2020 ◽  
Vol 643 ◽  
pp. L10
Author(s):  
N. Rambaux ◽  
J. C. Castillo-Rogez
Keyword(s):  
Kuiper Belt ◽  
Hydrostatic Equilibrium ◽  
The Body ◽  
Giant Planets ◽  
Third Order ◽  
Global Shape ◽  
Low Degree ◽  
Cassini Mission ◽  
Clairaut Equation ◽  
Shape Characteristics

Context. Phoebe is an irregular satellite of Saturn, and its origin, from either between the orbits of the giant planets or the Kuiper Belt, is still uncertain. The extent of differentiation of its interior can potentially help inform its formation location because it is mainly determined by heat from 26-aluminum. The internal structure is reflected in the shape, assuming the body is relaxed to hydrostatic equilibrium. Although previous data analysis indicates Phoebe is close to hydrostatic equilibrium, its heavily cratered surface makes it difficult to tease out its low-order shape characteristics. Aims. This paper aims to extract Phoebe’s global shape from the observations returned by the Cassini mission for comparison with uniform and stratified interior models under the assumption of hydrostatic equilibrium. Methods. The global shape is derived from fitting spherical harmonics and keeping only the low-degree harmonics that represent the shape underneath the heavily cratered surface. The hydrostatic theoretical model for shape interpretation is based on the Clairaut equation developed to the third order (although the second order is sufficient in this case). Results. We show that Phoebe is differentiated with a mantle density between 1900 and 2400 kg m−3. The presence of a porous surface layer further restricts the fit with the observed shape. This result confirms the earlier suggestion that Phoebe accreted with sufficient 26-aluminium to drive at least partial differentiation, favoring an origin with C-type asteroids.

A peek into Jupiter’s normal modes from Juno gravity data

2021 ◽  
Author(s):  
Daniele Durante ◽  
Luciano Iess
Keyword(s):  
Gravity Field ◽  
Gravity Data ◽  
Normal Modes ◽  
Integration Time ◽  
Interior Structure ◽  
Axially Symmetric ◽  
Error Sources ◽  
Physical Constraints ◽  
Doppler Data ◽  
Very High

<p>As of April 2021, Juno is close to complete its nominal mission, awaiting to enter its extended mission. Thanks to the extremely accurate Doppler data (having an accuracy as low as 10 micron/s at an integration time of 60 s) acquired during close perijove passes in the last 4 years, Juno provided an unprecedented view of Jupiter’s gravity field, which is crucial to determine its interior structure. In order to recover the gravity field of the planet, the orbits of Juno have to be reconstructed to a very high accuracy. The latest gravity field reconstruction showed hints to a non-static and/or non-axially symmetric field, possibly related to several different phenomena, such as normal modes, localized atmospheric or deeply-rooted dynamics. These tiny phenomena produces a residual signal at a level of few tens of micron/s in Juno Doppler data. To confidently study these tiny unconventional phenomena, the dynamical model of Juno’s spacecraft have been accurately characterized and possible error sources investigated and ruled out.</p><p>The focus of this study is Jupiter’s normal modes. Our main goal is to assess whether the residuals signatures can be explained by the gravitational disturbances induced by normal modes inside the planet, assuming reasonable physical constraints. Ground-based observations of Jupiter’ normal modes can be used as a guide.</p>

Differenzierungen im Begriff, Gegenwart‘ bei Husserl und Merleau-Ponty

2017 ◽  
Vol 2017 (1) ◽  
pp. 39-54
Author(s):  
Jörg Zimmer
Keyword(s):  
Modern Philosophy ◽  
The Body ◽  
Fundamental Concept ◽  
Phenomenological Description ◽  
Philosophy Of Time ◽  
Phenomenology Of Perception ◽  
The World ◽  
Classical Philosophy ◽  
The Moment ◽  
Empty Time

In classical philosophy of time, present time mainly has been considered in its fleetingness: it is transition, in the Platonic meaning of the sudden or in the Aristotelian sense of discreet moment and isolated intensity that escapes possible perception. Through the idea of subjective constitution of time, Husserl’s phenomenology tries to spread the moment. He transcends the idea of linear and empty time in modern philosophy. Phenomenological description of time experience analyses the filled character of the moment that can be detained in the performance of consciousness. As a consequence of the temporality of consciousness, he nevertheless remains in the temporal conception of presence. The phenomenology of Merleau-Ponty, however, is able to grasp the spacial meaning of presence. In his perspective of a phenomenology of perception, presence can be understood as a space surrounding the body, as a field of present things given in perception. Merleau-Ponty recovers the ancient sense of ‘praesentia’ as a fundamental concept of being in the world.

scholarly journals Spinning rough disc moving in a rarefied medium

2010 ◽  
Vol 466 (2119) ◽  
pp. 2033-2055 ◽  
Author(s):  
Alexander Plakhov ◽  
Tatiana Tchemisova ◽  
Paulo Gouveia
Keyword(s):  
The Body ◽  
Two Dimensional ◽  
Zero Temperature ◽  
Optimal Mass Transport ◽  
Dense Gases ◽  
Magnus Effect ◽  
Inverse Effect ◽  
Transversal Force ◽  
The Moment ◽  
Complementary Mechanism

We study the Magnus effect: deflection of the trajectory of a spinning body moving in a gas. It is well known that in rarefied gases, the inverse Magnus effect takes place, which means that the transversal component of the force acting on the body has opposite signs in sparse and relatively dense gases. The existing works derive the inverse effect from non-elastic interaction of gas particles with the body. We propose another (complementary) mechanism of creating the transversal force owing to multiple collisions of particles in cavities of the body surface. We limit ourselves to the two-dimensional case of a rough disc moving through a zero-temperature medium on the plane, where reflections of the particles from the body are elastic and mutual interaction of the particles is neglected. We represent the force acting on the disc and the moment of this force as functionals depending on ‘shape of the roughness’, and determine the set of all admissible forces. The disc trajectory is determined for several simple cases. The study is made by means of billiard theory, Monge–Kantorovich optimal mass transport and by numerical methods.

Calling Time Out in Doha: The Seiko Block Camera and Image Ethics

2021 ◽  
pp. 019685992110408
Author(s):  
David Staton
Keyword(s):  
International Association ◽  
Ethics Of Care ◽  
The Body ◽  
Camera Angle ◽  
Time Out ◽  
Related Idea ◽  
The Moment

In an effort to put more eyeballs on television sets, and in an attempt to reinvigorate a sport long beleaguered by doping scandals, recent questions surrounding female sponsorships, and a vanishing audience, the International Association of Athletic Federations unveiled a new camera designed by Seiko during the September 2019 World Championships held in Doha, Quatar. The idea was to add to an immersive experience, offering unparalleled views of sprinters at the moment they exploded from the starting blocks. Like many things during the Doha meet, the effort became an ending to a bad joke. Rather than getting to the heart of the event, the camera’s focus was a bit lower; the Seiko angle became known derisively as the crotch shot. After objections by two female German sprinters the positioning of the camera angle (specifically what would be shown when) was reconsidered, reframed, and essentially retired. Control of the body, including how it is observed, and the closely related idea of the control of one’s image are bound by certain ethical dimensions, particularly when that control is violated or profited from by outside parties. This paper interrogates how those concerns may be ameliorated by embracing an ethics of care.

scholarly journals Reflexive Dressing: Rethinking Retro

2016 ◽  
Vol 22 (1) ◽  
Author(s):  
Stella North
Keyword(s):  
Subjective Experience ◽  
The Body ◽  
The Past ◽  
Present Experience ◽  
The Moment

This article undertakes a philosophical exploration of the act we know, or think we know, as ‘dressing’. Inhabiting, in thought, the moment in which we dress, I examine some of its constituent mechanisms, attending to the impulses by which dressing is generated out of subjective experience.  When those impulses are temporally marked, as they are in the case of retro dress, this generation is a two-pronged process, in which the holding of the body in time, and the holding of time in the body, recalibrate one another. The process of ‘dressing,’ in this understanding, has a reflexivity which is double; it entails the turning of the body, with dress as medium, towards itself, and the turning of present experience towards some felt notion of the past. Reflexively dressing, we are always becoming ourselves, and becoming other than ourselves, at once; a movement of circuitous internalisation and externalisation by which the ambiguation inherent in material experience is realised.  

Signature of Phobos’ interior structure in its gravity field and libration

Icarus ◽  
2019 ◽  
Vol 321 ◽  
pp. 272-290 ◽  
Author(s):  
S. Le Maistre ◽  
A. Rivoldini ◽  
P. Rosenblatt
Keyword(s):  
Gravity Field ◽  
Interior Structure

scholarly journals Analytical and Experimental Analysis of a Free Link in Contact with a Granular Medium

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Dan B. Marghitu ◽  
Seung Lee
Keyword(s):  
Granular Medium ◽  
Stopping Time ◽  
The Body ◽  
Resistance Force ◽  
Time Interval ◽  
The Moment ◽  
Static Resistance ◽  
The Impact ◽  
Resistance Forces ◽  
Empirical Approaches

In this study, the experimental and the simulation results for a planar free link impacting a granular medium are analyzed. The resistance force of the granular medium on the body from the moment of the impact until the body stops is very important. Horizontal and vertical static resistance forces developed by theoretical and empirical approaches are considered. The penetrating depth of the impacting end of the free link increases with the increase of the initial impacting velocity. We define the stopping time as the time interval from the moment of impact until the vertical velocity of the link end is zero. The stopping time of the end decreases as the initial velocity increases. The faster the end of the link impacts the surface of the granular medium, the sooner it will come to a stop. This phenomenon involves how rapidly a free link strikes the granular medium and how it slows down upon contact.

scholarly journals Embodied Intersubjectivity and the Vitality of Cultural Meaning: Narratives of Communicative Musicality in Learning and Teaching

2019 ◽  
Author(s):  
Stephen Malloch ◽  
Jonathan Delafield-Butt ◽  
Colwyn Trevarthen
Keyword(s):  
Human Nature ◽  
Technical Skills ◽  
Human Learning ◽  
The Body ◽  
Cultural Meaning ◽  
Learning And Teaching ◽  
The Moment ◽  
Structure Knowledge ◽  
Embodied Intersubjectivity ◽  
Motor Structure

Human learning is inspired with the purposes and feelings of individuals who seek conscious, in-the-moment cooperation. It is social and co-created through mutual attunement of the movements of body and mind. In school, the interested learner needs to be encouraged by a skilled teacher sensitive to the rhythms of the child’s friendly, open vitality. They co-create shared projects in play, with movement and language, developing meaning and learning in sympathetic collaboration. From infancy, projects of imagination are expressed by the body and voice with the creative forms of 'communicative musicality' – gestural narratives created in rhythms of movement, felt, seen and heard. They anticipate being responded to with love and care. Learning within these embodied narratives incorporates affective, energetic, and intentional components to produce schemas of engagement that structure knowledge, and become meaningful habits held in memory. The rituals of culture and technical skills develop from the psycho-motor structure of human nature, with its vital impulses of thought-in-action that express an integrated, imaginative, and sociable Self.

Sign in / Sign up

Export Citation Format

Share Document