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  • 1
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    Orbital stability of the unseen solar companion linked to periodic extinction events (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Evidence from three-dimensional numerical modelling is presented that only cometary orbits with a limited range in inclination with respect to the galactic plane are formally stable for the length of time required to cause periodic extinction events. The calculations were done using Cowell's method employing a fourth-order Runge-Kutta integration scheme in an inertial reference frame in orbit about the Galaxy. Tidal perturbations in the radial direction due to the Galaxy and the Coriolis forces are included. The vertical component of the gravitational field of the galactic disk is superimposed on these forces. The results indicate that orbits for Nemesis that are inclined at more than 30 deg to the galactic plane are not allowed and suggests that the search for Nemesis should be concentrated toward the plane of the Galaxy. Perturbations by passing stars or molecular clouds may make even the low-inclination orbits unstable.
    Keywords: ASTRONOMY
    Type: Nature (ISSN 0028-0836); 311; 641
    Format: text
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  • 2
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    Continuing investigation of sweeping Jovian resonances - The 7:3 amd 3:2 resonances with further discussion of the 2:1 resonance (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The formation of the solar system from an accretion disk around the protosun can have a significant impact on the celestial mechanics of the early solar system. The solids in the disk settled to the midplane and formed a planetesimal swarm while an early-formed Jupiter was present. The gravity of the disk makes the radial force law become non-Keplerian, causing the commensurability resonances of the early-formed Jupiter to be displaced from where they would otherwise be. An analysis similar to that previously applied to the 2:1, 3:1 and 5:2 resonances is presently undertaken for the 7:3 and 3:2 resonances, and a Kirkwood-like gap is obtained for a sweeping 7:3 resonance. An accumulation of objects is obtained near the 3:2 resonance which, with the ejection of objects on either side of the resonance, would resemble the Hilda group of asteroids. Agreement between the exact commensurability location and the gap center is discussed for the 2:1 resonance.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 127; 2
    Format: text
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  • 3
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    The boundary of the solar system (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The shape of the boundary of the solar system, defined as the surface within which the gravitational attraction of the sun rather than that of the rest of the Galaxy controls the orbital motion of planets and comets, has been determined. Outside of this surface, the dominant factors are the radial tides due to the galactic center and the vertical tides caused by the galactic disk. Orbits which are direct with respect to the galactic plane have a boundary which differs from that for retrograde orbits, both being 10-20 percent oblate and both larger than the present Oort cloud. The surface may have been the boundary of the early cloud of comets which was later reduced by the passages of stars and molecular clouds.
    Keywords: ASTRONOMY
    Type: Nature (ISSN 0028-0836); 311; 38
    Format: text
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  • 4
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    The out-of-plane distribution of zodiacal dust near the earth (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: Analysis of IRAS data of the thermal zodiacal emission reveals an out-of-plane dust distribution near the Earth which is well-represented by a Lorentzian function. We suggest a possible explanation for the similarity as near-Earth gravitational perturbations of dust grains. Such perturbations are expected to be chaotic and will randomize any residual band structure near the Earth.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 105; 3; p. 976-979.
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