Pair Of Satellites Research Articles

Towards a theory for the uranian rings

Interparticle collisions, radiation drag and differential precession all tend to disrupt the rings of Uranus. The first two effects lead to radial spreading which would disrupt a free ring in ≲ 10^8 yr. We propose that the rings are confined in radius by gravitational torques from a series of small satellites that orbit within the ring system. Differential precession tends to destroy the apse alignment of the elliptical e ring. We suggest that apse alignment is maintained by the self-gravity of the ring. The resulting mass of the e ring is ~5 × 10^(18) g. Its radial confinement requires (for example) a pair of satellites of mass ~10^(19) g, in circular orbits roughly 500 km away on either side of the ring.

Theories of Resonant Satellite Pairs in Saturn's System

Upcoming missions to the outer planets have made evident the need for better theories of their satellites. We have been involved in an effort to provide better satellite theories through new observations (Abbot, Mulholland and Shelus 1975; Mulholland, Shelus and Abbot 1976; Mulholland and Shelus 1977; and Benedict, Shelus and Mulholland 1978), and new analytical theories (Jefferys and Ries 1975; Jefferys 1976. Hereinafter these are denoted Paper I and Paper II, respectively). In this paper we report on our incorporation of new and old observations into our theories, and on our progress on the theoretical front.

Multiple‐satellite studies of magnetospheric substorms: Plasma sheet recovery and the poleward leap of auroral zone activity

Particle observations from pairs of satellites (Ogo 5 and Vela 4A and 5A) during 28 plasma sheet thickening events are examined. These data indicate that thickening of the nighttime plasma sheet during substorms occurs in two main stages, one early stage of single or multiple expansions of the near‐earth (geocentric distances r ≲15 RE) plasma sheet at the onset of substorm expansions (Pi 2 bursts) on the ground and another later stage of plasma sheet recovery that starts near the time of maximum auroral zone bay activity and is characterized by a large‐scale thickening toward higher latitudes that occurs over a broad azimuthal scale and from ionospheric heights to beyond the Vela orbit (r ∼18 RE). A detailed analysis of two‐satellite observations during eight plasma sheet recoveries is presented, showing events that occurred within 5 min in widely separated locations at small (<4 RE) distances from the tail's midplane and events that occurred concurrently in the Vela orbit and at high latitudes in the near‐earth region. Some events were accompanied by clear signatures of a poleward leap (to >71° magnetic latitude) of electron precipitation and the westward electrojet that probably corresponded to an expansion poleward of the ionospheric projection of the recovering plasma sheet. The eight plasma sheet recoveries occurred 10–30 min after a Pi 2 burst on the ground, and mid‐latitude magnetograms showed no indications of a near‐coincident formation of a substorm current wedge in the local time sector of the spacecraft; this indicates that the plasma sheet recoveries and the poleward leaps were not caused directly by a late high‐latitude substorm expansion. Instead, these phenomena seem to represent a transition phase between a substorm expansion sequence and a substorm recovery.

Resonance orbits and the rings of Uranus

SOON after the discovery of the rings of Uranus1–3 it was suggested4 that the ring system might be determined by the perturbations of the satellite pairs Ariel–Titania and Ariel–Oberon. Aksnes5, and Goldreich and Nicholson6 have questioned this hypothesis; the latter showing that the strongest perturbations on the ring system can be expected to arise from the satellite pair Miranda-Ariel and the 4 : 1 resonance of Miranda. Goldreich and Nicholson also pointed out that the differences in the ring radii α–β, γ–δ and e1–e2 are known to a high degree of accuracy (typically ∼±15 km) which is considerably better than the absolute ring radii. My calculations of the separations of these ring pairs reported here suggest that the radii of the α and γ rings, and perhaps the e1 and e2 components as reported by Elliott et al.1, are governed by the resonances of Miranda and Ariel, with consistent further application of resonance theory to the location of the β and δ rings requiring the presence of an additional hypothetical satellite moving around Uranus. Without this hypothesis the observed ring system seems to be outside the scope of resonance theory alone.

New Orbits for Enceladus and Dione Based on the Photographic Observations

AbstractA program is underway at the McDonald Observatory to extend the series of photographic observations of the satellites of the outer planets (Abbot, Mulholland and Shelus, A.J. 80, 1975), and concurrent theoretical studies have led to a new orbital theory for the resonant pair of satellites, Enceladus and Dione (Jefferys and Ries, A.J. 80, 1975). The construction of the new theory, using the computer software system TRIGMAN, has provided Fortran subroutines for the computation of the planetocentric coordinates of the two satellites, as well as partial derivatives for the orbit elements and certain other physical parameters of the orbit problem, including some of the harmonics of the gravitational field of Saturn. The available photographic observations for these two objects are currently being discussed with the new theory, and improved values of the orbital parameters are expected in the near future.

Quantitative analysis of the Dermott–Gold theory for Uranus's rings

A summary is presented of an investigation which supplements the largely qualitative analysis conducted by Dermott and Gold (1977). Dermott and Gold have attempted to explain the locations of Uranus's rings in terms of resonances between ring particles and pairs of satellites. An equation of motion, analogous to that of a pendulum, is derived, taking into account a study by Wilkens (1933) of possible three-body resonances involving one minor and two major planets. Dermott and Gold had concluded that the observed pattern is probably due primarily to the effect of Ariel-Titania and Ariel-Oberon pairs. However, on the basis of the values derived in the reported investigation it is seen that Miranda plays the key role rather than Ariel, in spite of the small mass of the former. It is concluded that a decisive test of the Dermott-Gold theory has to await further observational details concerning the Uranus's rings.

Revenge of tiny Miranda

DERMOTT and Gold have proposed a resonance model for the rings of Uranus. They assume the rings are, in fact, arcs composed of small particles librating about stable resonances determined by pairs of satellites, either Ariel and Titania or Ariel and Oberon. Dermott and Gold dismiss as insignificant resonances involving tiny Miranda. We report here that, by a wide margin, the strongest resonances are all associated with Miranda. Furthermore, we show that the hypothesis that the rings are made up of librating particles, while original and ingenious, is incorrect.

Application of spin-orbit theory to a class of orbit-orbit resonances: The case of Titan-Hyperion

The orbit-orbit interaction of two satellites of greatly unequal mass is studied under the condition that the more massive satellite moves in a circular (unperturbed) orbit that lies entirely inside the orbit of the smaller (perturbed) body. It is shown that this system is equivalent in every respect to a special case ofspin-orbit coupling. On this basis, conditions for resonance are derived, as well as libration periods and bandwidths. Application is made to Saturn's resonant pair of satellites, Titan and Hyperion, which approximate the conditions of this problem. The calculated libration period of 646 days is in reasonably good agreement with the observed 640-day period.

Nuclear quadrupole resonance in the interaction representation

Using the interaction representation, the transient pulsed response of an ensemble of nuclei with spin I=3/2 experiencing electric quadrupole couplings is calculated, both in zero field and in the presence of a weak, applied static field. It is found that, in this representation, the evolution of the density operator depends, to a good approximation, on a time-independent effective hamiltonian. For the response to a solitary, resonant 90° pulse, the prediction is made of the existence of two transient decay signals, 90° out of phase with each other, one being determined by the even moments of the absorption line (as in the ordinary N.M.R. case) and the other being determined by the odd moments. This second signal will be present in the N.Q.R. case, since here the effect of dipole-dipole couplings seems to be, in general, to broaden the resonance line at ω0 asymmetrically, and while the first moment can be proved to be always zero, this is not, in general, true of the higher odd moments. Expressions are derived from which, in principle, any even or odd moment may be calculated. As another example of the use of the interaction representation in N.Q.R., the effect of a weak applied static magnetic field is considered and it is shown that the response to a single 90° pulse is modulated by two frequencies associated with the known splitting of the c.w. absorption line into two pairs of satellites. Using the interaction representation formalism, the response of the ensemble to the Slichter-Holton and Lee-Goldburg pulse sequences (considered previously by the author) is also investigated. Lastly, it is shown how a two-pulse sequence, identical to that previously used by other investigators for the same purpose in N.M.R., may be used to overcome the ‘dead-time’ problem associated with pulsed work and enable one, to a good approximation, to observe the N.Q.R. free induction decay from an effective time zero.

The nucleolar cycle in man.

Tissue cultures of human embryonal kidney and ovary were examined. In the nuclei of both tissues, one to ten nucleoli have been found. The maximum number of nucleoli is connected with the gene expression of rDNA of the 10 nucleolus organizers of chromosome pairs Nos. 13, 14, 15, 21 and 22, which have secondary constrictions and are the satellite chromosomes in man. The small percentage of cells with 10, 9 and 8 nucleoli is attributed to the rapid association of 3 of the homologous acrocentrics (perhaps of group D). Two of the satellite (SAT) pairs probably associate later after mitosis. The process of fusion is dynamic, resulting in one interphase nucleous--a manifestation of the association of all SAT chromosomes. Dissociation of the nucleolus occurs upon entering prophase, due to the condensation of the chromosomes and retreat of rDNA to the respective secondary constrictions. As a result, the nucleolar number increases again. The pattern of the nucleolar kinetics within the course of one mitotic division is described.

Orbital Resonances in the Solar System

Orbital resonances are defined as any system of two or more satellites (including planets) orbiting the same primary and whose orbital mean motions are in a ratio of small whole numbers. Known orbital resonances in the solar system are identified, including those involving Jupiter's satellites Io, Europa, and Ganymede; Saturn's satellites Mimas and Tethys, Enceladus and Dione, and Titan and Hyperion; Saturn's ring gaps and Mimas; various asteroids and Jupiter; and the planets Neptune and Pluto. The stability of orbital resonances is examined, the origin of orbital commensurabilities is investigated, and a simple model of the simplest kind of eccentricity-type resonance is outlined. A method is described by which tides carry a noncommensurate pair of satellites into a stable libration, and current ideas concerning the formation of the gaps in Saturn's rings and the asteroid belt are discussed. Various approaches to the analysis of orbital resonances are laid out and illustrated. Three two-body commensurabilities in Saturn's satellite system are analyzed numerically.

Mutual phenomena of the Galilean satellites in 1973. III - Final results from 91 light curves

This paper presents an analysis of photoelectric light curves of 91 mutual eclipses and occultations of the Galilean satellites that occurred from June to December 1973. From the deepest curves, radii and standard errors are deduced for J2, J3, and J4. It is shown that the substantial differences between the depths and midtimes observed and those predicted by Sampson's theory can be used in a clear and definite way to revise the orbital constants of that theory. The present analysis, which reduces all the data provided by these mutual events in one body, diminishes the latitude and longitude residuals of the unrevised theory by as much as a factor of about 10. The resulting overall consistency and the demonstrated inadequacy of an explanation based solely on surface-brightness variations argue that these corrections do represent the dominant effects required to account for the light curves. In order that these mutual events can be used with other astrometric data, the separations between a satellite pair at midevent are given. A small systematic (with solar phase angle) and unexplained difference in the longitude corrections is found for Io and Europa as obtained from nearly simultaneous pairs of occultations and eclipses.

Multiple propagation paths between satellites situated in the ionosphere below the f-layer peak

Theoretical results which show that up to six different propagation paths are possible at the same frequency between a pair of satellites at an equal height below the peak of a biparabolic concentric model ionosphere are presented. The path changes that arise for different satellite separations are discussed.

Location of nucleolar organizing regions on the chromosomes of the Syrian hamster <i>(Mesocricetus auratus</i>) and the Djungarian hamster <i>(Phodopus sungorus</i><i>)</i>

Terminal chromosome associations ("satellite associations") in ASG-banded preparations have been used to determine the number and location of staellites in the Syrian hamster (Mesocricetus auratus) and the Djungarian hamster (Phodopus sungorus). Five pairs of satellites are found in the former and four in the latter. Nucleolar organizing regions (NORs) were visualized with the Ag-AS silver precipitation technique, and their number and position corresponded exactly with the number and position of satellites in Phodopus, where positive chromosome identification can be made in the absence of banding. Numerical agreement is exact in Mesocricetus as well, and the morphology of the silver-tagged NOR-bearing chromosomes strongly suggests that corrrespondence also occurs in this species.

Establishment and evolution of satellite-satellite resonances

Recent papers by Greenberg and Sinclair have lent support to Goldreich's tidal hypothesis which provides an explanation for the existence of several orbit-orbit resonances among the satellites of Saturn and Jupiter. In this paper I show that near resonance the two-body interaction appropriate to the three resonances observed in Saturn's system can be adequately described by a one dimensional Hamiltonian. A slow variation in the semimajor axes is then introduced to provide the evolution. First I determine the specific relationship between the initial inclination/eccentricity and the masses, etc., which separate direct capture (a la Greenberg) from a probabilistic capture (a la Sinclair). Once a resonance is established, I show that the action integral can be used to analytically follow the evolution of the libration amplitude as a function of the change in the semimajor axes, as was first done by Allan for the Mimas-Tethys case. The secular changes in the semimajor axes suggested by the presently observed libration amplitude are compared with their maximum tidal change using Goldreich's value forQ. I find that the tidal mechanism is insufficient only in the Titan-Hyperion case. I discuss the possibitility that satellite accretion may have produced the requisite evolution in Titan's orbit. Finally I show that both the stability and capture mechanisms for the three-body resonance among Jupiter's inner satellites depend on the observed near commensurability of the inner and outer pairs of satellites.

Signal to noise ratio in a satellite gravitational wave experiment

A system for detection of gravitational radiation is proposed which consists of a widely-separated pair of drag-free satellites. Variations in their relative velocity induced by gravitational waves would be detected by a Doppler-ranging system. It is shown that the sensitivity of such a system can be sufficient to allow detection of gravitational radiation from high-density star clusters near the galactic center.

Mathematical Models for the Combination of Terrestrial and Satellite Networks

This paper reviews and analyzes some existing mathematical models used for the combination of terrestrial and satellite networks. They all contain three rotations, three translations and a scale factor, but differ in the choice of the point at which the rotations are made. Also, an alternative model is developed. It contains the above seven parameters and an additional set of rotations to account for systematic errors in the networks. An estimation technique is proposed for the separation of system and network rotations. Finally, an adjustment technique for the combination of pairs of satellite and terrestrial networks to yield a solution from all possible data is outlined.

Methansulfono-bis(methylimid)-methylamidostannane: ein neuer molekültyp mit fluktuierenden bindungen : Synthese und 1H-NMR-spektroskopische untersuchungen

Methanesulfonobis(methylimide)methylamidostannanes of the general composition Me n Sn[MeS(NMe) 2NMe] 4- n ( n = 0, 1, 2 or 3) were prepared by transamination of stannylamines Me n Sn(NMe 2) 4- n ( n = 0, 1, 2 or 3) with methanesulfonobis)methylimide)methylamide, MeS(NMe) 2NHMe. The proton resonance spectra of these compounds show in the temperature range from -60° to +110° only a single signal for the methyl protons linked to nitrogen, and two satellite pairs belonging to the 1HCN 117/119Sn-coupling. Their intensities relative to the main signal are in accord with the natural concentration of the tin isotopes 117Sn and 119Sn. The spectroscopic data suggest intramolecular exchange phenomena similar to the observation made with cyclopentadienyl derivatives of the heavy elements in Group IVB.

Reply [to “Comment on ‘The direct mapping of gravity anomalies using Doppler tracking between a satellite pair’ by Gary C. Comfort”

Reply [to “Comment on ‘The direct mapping of gravity anomalies using Doppler tracking between a satellite pair’ by Gary C. Comfort”

Comment [on “The direct mapping of gravity anomalies using Doppler tracking between a satellite pair” by Gary C. Comfort

Comment [on “The direct mapping of gravity anomalies using Doppler tracking between a satellite pair” by Gary C. Comfort