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  • 1
    Electronic Resource
    Electronic Resource
    Gravitationally unbound comets move in predominantly retrograde orbits (1991)
    [s.l.] : Nature Publishing Group
    Nature 352 (1991), S. 506-508 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The orbit of a comet may be bound (elliptic) or unbound (hyperbolic). Its dimensions are characterized by the semimajor axis, a, and the orbital energy is proportional to —I/a. For the Earth, a = 1 AU 1.5 x 108 km. Oort concluded from the evidence of 19 well-determined ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/352506a0
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  • 2
    Electronic Resource
    Electronic Resource
    Why we study the geological record for evidence of the solar oscillation about the galactic midplane (1996)
    Springer
    Earth, moon and planets 72 (1996), S. 7-12 
    Details
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Solar System oscillates about the plane defined by the disk of matter in our Galaxy. This oscillatory motion gives rise to a substantial modulation in the tidally induced flux of Oort cloud comets. An observational determination of the quasi-periodicity of this motion carries with it significant information about the population, distributions, dynamics and origins of short-period and long-period comets. An additional incentive for emphasizing such a study is the information about dark disk matter that a period can yield. If dark disk matter is completely negligible, the amplitude of the solar motion will be sufficiently large that the peak-to-trough flux ratio will be ≈ 2.5 and the plane-crossing period will exceed 40 Myr. Dark disk matter comparable in mass to bright disk matter and distributed in any manner is inconsistent with K-dwarf distributions and can be rejected as a working hypothesis. But if a modest fraction of the disk matter is dark and distributed like the interstellar medium, as is consistent with limits deduced from K-giant and K-dwarf velocity distributions, the peak-to-trough flux ratio can increase to a factor of 4 even though the solar z amplitude is decreased. In that case the period can be as little as 30 Myr and the implied Oort population is smaller by a factor of 3. We should carefully reconsider the geological record as a potential discriminator of these options.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00117495
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  • 3
    Electronic Resource
    Electronic Resource
    Periodic comet showers and planet X (1985)
    [s.l.] : Nature Publishing Group
    Nature 313 (1985), S. 36-38 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] During the lifetime of the Solar System, planet X will have swept out a gap in the comet disk of width determined by its perihelion and aphelion distances4. Assuming the planet's orbit has modest eccentricity and inclination to the planetary plane, then the perihelion (aphelion) will pass close to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/313036a0
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  • 4
    Electronic Resource
    Electronic Resource
    Periodic comet showers and planet X (1985)
    [s.l.] : Nature Publishing Group
    Nature 313 (1985), S. 744-744 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - In our recent Nature paper we discussed a model in which periodic comet showers are triggered by the passage of the perihelion of planet X through the edge of a trans-Neptune comet disk (Nature 313, 36-38; 1985). It was assumed that all scattered comets with perihelia less than Neptune's ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/313744a0
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  • 5
    Electronic Resource
    Electronic Resource
    Supermassive binaries in active galactic nuclei (1981)
    [s.l.] : Nature Publishing Group
    Nature 293 (1981), S. 722-724 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Jet precession and evolutionary considerations led Begelman, Blandford and Rees7 to propose a binary model containing two MBHs in which the observed jet motion is identified with the geodetic precession of the more massive component (Mi 108M). Although this model can account for the inversion- ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/293722a0
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  • 6
    Electronic Resource
    Electronic Resource
    Generalized Lagrangian orbital elements for central force problems (1985)
    Springer
    Celestial mechanics and dynamical astronomy 36 (1985), S. 71-82 
    Details
    ISSN: 1572-9478
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider the definitions and resulting equations of motion for the Lagrangian orbital elements associated with conventional osculating orbit theory for central forces. The analysis indicates that the definitions themselves lead to difficulties which are most apparent in the circular limit. An alternate set of defining relations is presented which eliminates the problems associated with osculating elements. The remaining equation of motion based on these new definitions is reduced to quadratures. This solution completely expresses the orbits for central force problems with no restriction on the eccentricity. Both bounded and open orbits are considered. A generalized Laplace-Runge-Lenz vector is developed and a number of example solutions are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01241043
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  • 7
    Electronic Resource
    Electronic Resource
    A model of the galactic tidal interaction with the oort comet cloud (1992)
    Springer
    Celestial mechanics and dynamical astronomy 54 (1992), S. 13-35 
    Details
    ISSN: 1572-9478
    Keywords: Hamiltonian mechanics ; Oort comet cloud ; galactic tidal torque
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider a model of the in situ Oort cloud which is isotropic with a random distrihution of perihelia directions and angular momenta. The energy distribution adopted has a continuous range of values appropriate for long-period (〉200 yr) comets. Only the tidal torque of the Galaxy is included as a perturbation of comet orbits and it is approximated to be that due to a quasi-steady state distribution of matter with disk-like symmetry. The time evolution of all orbital elements can be analytically obtained for this case. In particular, the change in the perihelion distance per orbit and its dependence on other orbital elements is readily found. We further make the assumption that a comet whose perihelion distance was beyond 15 AU during its last passage through the Solar System would have orbit parameters that are essentially unchanged by planetary perturbations. Conversely, if the prior passage was inside 15 AU we assume that planetary perturbations would have removed the comet from the in situ energy distribution accessible by the galactic tide. Comets which had their perihelia changed from beyond 15 AU to within 5 AU in a single orbit are taken to be observable. We are able to track the evolution of 106 comets as they are made observable by the galactic tidal touque. Detailed results are obtained for the predicted distribution of new (0 〈 1/α 〈 10−4 AU−1) comets. Further, correlations between orbital elements can be studied. We present predictions of observed distributions and compare them with the random in situ results as well as with the actual observed distributions of class I comets. The predictions are in reasonable agreement with actual observations and, in many cases, are significantly different from random when perihelia directions are separated into galactic northern and southern hemispheres. However the well-known asymmetry in the north-south populations of perihelia remains to be explained. Such an asymmetry is consistent with the dominance of tidal torques today if a major stochastic event produced it in the past since tidal torques are unable to cause the migration of perihelia across the latitude barriers ±26°.6 in the disk model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00049541
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  • 8
    Electronic Resource
    Electronic Resource
    Oort Cloud Comet Perihelion Asymmetries: Galactic Tide, Shower or Observational Bias? (1997)
    Springer
    Celestial mechanics and dynamical astronomy 69 (1997), S. 77-87 
    Details
    ISSN: 1572-9478
    Keywords: Oort comet cloud ; galactic tide ; comet showers ; observational selection effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We investigate the distribution of Oort cloud comet perihelia. The data considered includes comets having orbital elements of the two highest quality classes with original energies designated as new or young. Perihelion directions are determined in galactic, ecliptic and geocentric equatorial coordinates. Asymmetries are detected in the scatter and are studied statistically for evidence of adiabatic galactic tidal dynamics, an impulse-induced shower and observational bias. The only bias detected is the well-known deficiency of observations with perihelion distances q 〉 2.5 AU. There is no significant evidence of a seasonal dependence. Nor is there a substantive hemispherical bias in either ecliptic or equatorial coordinates. There is evidence for a weak stellar shower previously detected by Biermann which accounts for ≈ 10% of the total observations. Both the q bias and the Biermann star track serve to weaken the evidence for a galactic tidal imprint. Nevertheless, statistically significant asymmetries in galactic latitude and longitude of perihelia remain. A latitude asymmetry is produced by a dominant tidal component perpendicular to the galactic disk. The longitude signal implies that ≈ 20% of new comets need an additional dynamical mechanism. Known disk non-uniformities and an hypothetical bound perturber are discussed as potential explanations. We conclude that the detected dynamical signature of the galactic tide is real and is not an artifact of observational bias, impulsive showers or poor data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008370131320
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  • 9
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    Why we study the geological record for evidence of the solar oscillation about the galactic midplane (1996)
    Springer
    Details
    Publication Date: 1996-02-01
    Print ISSN: 0167-9295
    Electronic ISSN: 1573-0794
    Topics: Geosciences , Physics
    Published by Springer
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  • 10
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    A Widebinary Solar Companion as a Possible Origin of Sedna-like Objects (2006)
    Springer
    Details
    Publication Date: 2006-08-13
    Print ISSN: 0167-9295
    Electronic ISSN: 1573-0794
    Topics: Geosciences , Physics
    Published by Springer
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