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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
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Cometary showers and unseen solar companions (reply) (1984)
    [s.l.] : Nature Publishing Group
    Nature 312 (1984), S. 381-381 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] WHITMIRE AND JACKSON REPLY-The contribution of shower cornets to the mean cratering rate need only be comparable to the (assumed) steady-state random contribution to produce a strong signal in the Fourier spectrum of dated craters. The number of terrestrial impacts resulting from a shower of 2 x ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/312381a0
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  • 5
    Electronic Resource
    Electronic Resource
    Are periodic mass extinctions driven by a distant solar companion? (1984)
    [s.l.] : Nature Publishing Group
    Nature 308 (1984), S. 713-715 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The putative extinction period, although uncertain by as much as 7 x 106 yr (ref. 1), places the companion roughly near aphelion at the present epoch. The aphelion distance is Q* = a* (\ +e*) ? 2a* ? 1.8 x 105 AU, which is near the outer boundary of the Oort comet cloud. Fossil ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/308713a0
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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Relativistic Precessions of Macroscopic Objects (1972)
    [s.l.] : Nature Publishing Group
    Nature 239 (1972), S. 207-207 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] If the gravitational field of a spinning disk is not neglected it is evident from the arguments concerning the Thomas rotation of a section of the disk1 that the above result holds for the analogous general relativistic rotations. If a small section of the disk (near the perimeter, say) was not ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/239207a0
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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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    Implication of our technological species being first and early: The anthropic selection effect of our technological youth (2018)
    Cambridge University Press
    Details
    Publication Date: 2018
    Description: 〈div data-abstract-type="normal"〉〈p〉In the previous paper (Whitmire 2017; hereafter Paper I) arguments were given which suggest that the 〈span〉typical〈/span〉 technological species is short-lived and that their demise coincides with the extinction of their planetary biosphere. This conclusion is based on two observations and one primary assumption. The observations are: (1) Our own technological species is the first such species to evolve on Earth and (2) we are early in the potential evolution of a technological species. The primary assumption is that we are a typical member (in age) of the reference class of 〈span〉all〈/span〉 extant technological species in the universe. In this Letter, I thoroughly discuss the anthropic selection effect that the predicted lifetime of the typical technological species would most likely first be made when a technological species is young, thus guaranteeing a predicted short lifetime, regardless of the actual typical lifetime. I argue here that this selection effect is equivalent to narrowly redefining the reference class to be 〈span〉only〈/span〉 early technological species and, although true, it is a logical tautology, correct by definition and does not invalidate the application of the Principle of Mediocrity assumption to the expanded reference class of 〈span〉all〈/span〉 technological species, as was done in Paper I. Several simple analogies are given to illustrate this point.〈/p〉〈/div〉
    Print ISSN: 1473-5504
    Electronic ISSN: 1574-3006
    Topics: Biology , Geosciences
    Published by Cambridge University Press
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  • 10
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    Implication of our technological species being first and early (2017)
    Cambridge University Press
    Details
    Publication Date: 2017
    Description: 〈div data-abstract-type="normal"〉〈p〉According to the Principle of Mediocrity, a cornerstone of modern cosmology, in the absence of any evidence to the contrary, we should believe that we are a typical member of an appropriately chosen reference class. If we assume that this principle applies to the reference class of all extant technological species, then it follows that other technological species will, like us, typically find that they are both the first such species to evolve on their planet and also that they are early in their potential technological evolution. Here we argue that this suggests that the typical technological species becomes extinct soon after attaining a modern technology and that this event results in the extinction of the planet's global biosphere.〈/p〉〈/div〉
    Print ISSN: 1473-5504
    Electronic ISSN: 1574-3006
    Topics: Biology , Geosciences
    Published by Cambridge University Press
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