Hostname: page-component-cd9895bd7-8ctnn Total loading time: 0 Render date: 2024-12-23T15:44:20.374Z Has data issue: false hasContentIssue false
  • English
  • Français

The formation and dynamical survival of the comet cloud

Published online by Cambridge University Press:  12 April 2016

Julio A. Fernández
Julio A. Fernández*
Affiliation:
Observatório do Valongo, U.F.R.J., Ladeira do Pedro Antonio, 43, 20.080 Rio de Janeiro, Brazil

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The theory of a huge reservoir of comets (the “comet cloud”) extending to almost interstellar distances is analyzed, paying special attention to its dynamical stability, formation process and orbital properties of the incoming cloud comets. The perturbing influence of passing stars and giant molecular clouds is considered. Giant molecular clouds may be an important perturbing element of the comet cloud, although they do not seem to change drastically former studies including only stellar perturbations. The more tightly bound inner portions of the comet cloud, say within 104 AU, would have withstood the disrupting forces over the age of the solar system. The theory of a primordial comet origin in the outer planetary region close to Neptune’s orbit is specially analyzed. A primordial comet origin is consistent with the cosmogonic view that a large amount of residual material was ejected during the last stage in the formation of the Jovian planets. The smooth diffusion in the energy space of bodies scattered by Neptune guarantees that most of them will fall in the narrow range of energies close to zero (near-parabolic orbits) where passing stars and GMCs can act effectively on them. The long time scales of ~109 yr required for bodies scattered by Neptune to reach near-parabolic orbits would indicate that the buildup of the comet cloud was an event that took place long after the planets formed. Depending on the field of perturbing galactic objects, it is possible to conceive that most scattered comets were stored in rather tightly bound orbits (a ~l04 AU), favoring the concept of their dynamical survival over several billion yr. Alternative theories of comet cloud formation, e.g. in-situ origin or interstellar capture, are also discussed. The main difficulty of the in-situ theory is to explain how comets could accumulate at large heliocentric distances where the density of the nebular material was presumably very low. The interstellar capture theory also meets severe dynamical objections as, for instance, the lack of observed comets with original strongly hyperbolic orbits and the extremely low probability of capture under most plausible conditions. Since our knowledge of the structure of giant molecular clouds and their frequency of encounters with the solar system is still very uncertain, the concept of capture of transient comet clouds during such encounters can be advanced very little beyond the speculative stage. Some other dynamical properties of relevance to theories of origin and structure of the comet cloud are also reviewed. We mention, for instance, the distribution of perihelion points on the celestial sphere. There seems to be here a well established deviation from randomness, although the debate on whether or not there is a preference of the perihelion clustering for the vicinity of the apex of the solar motion is still unsettled. The alleged correlation with the solar apex may be biased by the preference of comet discoveries in the northern hemisphere. Deviations from randomness might be caused by very close stellar passages in the recent past. The excess of retrograde orbits among the observed “new” and young comets - mainly those with q ≳ 2 AU - is another well known dynamical feature. Such an excess may probably be accounted for by the combined action of planetary and stellar perturbations. Because of the decreasing action of planetary perturbations with increasing heliocentric distances, a significant increase in the rate of passages of long-period comets is predicted for the outer planetary region.

Type
Section II. The Oort Cloud of Comets
Information
International Astronomical Union Colloquium , Volume 83: Dynamics of Comets: Their Origin and Evolution , 1985 , pp. 45 - 70
Copyright
Copyright © Cambridge University Press 1985

References

Abt, H.A., and Levy, S.G. 1976. ‘Multiplicity among solar-type stars’. Astrophys. J. Suppl. 30, 273–306.CrossRefGoogle Scholar
Bailey, M.E. 1983a. ‘The structure and evolution of the Solar System comet cloud’. Mon. Not. Roy. Astron. Soo. 204, 603–633.CrossRefGoogle Scholar
Bailey, M.E. 1983b. ‘Theories of cometary origin and the brightness of the infrared sky’. Mon. Not. Roy. Astron. Soc. 205, 47p–52p.CrossRefGoogle Scholar
Bailey, M.E., McBreen, B., and Ray, T.P. 1984. ‘Constraints on cometary origins from isotropy of the microwave background and other measurements’. Mon. Not. Roy. Astron. Soc. 209, 881–888.CrossRefGoogle Scholar
Biermann, L. 1978. ‘Dense interstellar clouds and comets’. Symp. on Important Advances in 20th Century Astronomy, Copenhagen.Google Scholar
Biermann, L., and Michel, K.W. 1978. ‘On the origin of cometary nuclei in the presolar nebula’. Moon Planets 18, 447–464.CrossRefGoogle Scholar
Bogart, R.S., and Noerdlinger, P.D. 1982. ‘On the distribution of orbits among long-period comets’. Astron. J. 87, 911–917.CrossRefGoogle Scholar
Byl, J. 1983. ‘Galactic perturbations on near-parabolic cometary orbits’. Moon Planets 29, 121–137.CrossRefGoogle Scholar
Cameron, A.G.W. 1973 ‘Accumulation processes in the primitive solar nebula’. Icarus 18, 407–450.CrossRefGoogle Scholar
Chebotarev, G.A. 1966. ‘Cometary motion in the outer solar system’. Soviet Astron. - AJ 10, 341–344.Google Scholar
Clube, S.V.M., and Napier, W.M. 1984. ‘Comet capture from molecular clouds: a dynamical constraint on star and planet formation’. Mon. Not. Roy. Astron. Soc. 208, 575–588.Google Scholar
Davis, M., Hut, P., and Muller, R.A. 1984. ‘Extinction of species byperiodic comet showers’. Nature 308, 715–717.CrossRefGoogle Scholar
Everhart, E. 1968. ‘Change in total energy of comets passing through the solar system’. Astron. J. 73, 1039–1052.CrossRefGoogle Scholar
Everhart, E. 1976. ‘The evolution of comet orbits’. In The Study of Comets. IAU Coll. No. 25 (Donn, B., Mumma, M., Jackson, W., A’Hearn, M., and Harrington, R., eds.) pp. 445–464, NASA SP-393.Google Scholar
Everhart, E., and Marsden, B.G. 1983. ‘New original and future cometary orbits’. Astron. J. 88, 135–137.CrossRefGoogle Scholar
Fernández, J.A. 1980. ‘Evolution of comet orbits under the perturbing influence of the giant planets and nearby stars’. Icarus 42, 406–421.CrossRefGoogle Scholar
Fernández, J.A. 1981a. ‘New and evolved comets in the solar system’. Astron. Astrphys. 96, 26–35.Google Scholar
Fernández, J.A. 1981b. ‘On the observed excess of retrograde orbits among long-period comets’. Mon. Not. Roy. Astron. Soc. 197, 265–273.CrossRefGoogle Scholar
Fernández, J.A. 1982. ‘Dynamical aspects of the origin of comets’. Astron. J. 87, 1318–1332.CrossRefGoogle Scholar
Fernández, J.A., and Ip, W.-H. 1981. ‘Dynamical evolution of a cometary swarm in the outer planetary region’. Icarus 47, 470–479.CrossRefGoogle Scholar
Fernández, J.A., and Ip, W.-H. 1983. ‘On the time evolution of the come tary influx in the region of the terrestrial planets’. Icarus 54, 377–387.CrossRefGoogle Scholar
Fernández, J.A., and Ip, W.-H. 1984. ‘Some dynamical aspects of the accretion of Uranus and Neptune: The exchange of orbital angular momentum with planetesimals’. Iearus 58, 109–120.Google Scholar
Fernández, J.A., and Jockers, K. 1983. ‘Nature and origin of comets’. Rep. Prog. Rhys. 46, 665–772.CrossRefGoogle Scholar
Gordon, M.A., and Burton, W.B. 1980. ‘The distribution and size of giant molecular clouds in the galaxy’ In Giant Molecular Clouds in the Galaxy. Third Gregynog Astrophys. Workshop (Solomon, P.M. and Edmuns, M.G., eds.) pp.25–39, Pergamon Press, Oxford.CrossRefGoogle Scholar
Hills, J.G 1982. ‘The formation of comets by radiation pressure in the outer protosun’. Astron. J. 87, 906–910.CrossRefGoogle Scholar
Hurnik, H. 1959. ‘The distribution of the directions of perihelia and the orbital poles of non-periodic comets’. Acta Astron. 9 207–221.Google Scholar
Ip, W.-W. 1977. ‘On the early scattering processes of the outer planets’. In Comets - Asteroids - Meteorites: Interrelations, Evolution and Origin (Delsemme, A.H., ed.) pp.485–490, Univ. of Toledo Press, Toledo, Ohio.Google Scholar
Joss, P.C. 1973. ‘On the origin of short-period comets’. Astron. Astrophys. 25, 271–273.Google Scholar
Kerr, R.H. 1961. ‘Perturbations of cometary orbits’. Proa. 4th Berkeley Symp. of Mathematical Statistics and Probability. Vol.3, pp.149–164, Univ. of California Press, Berkeley.Google Scholar
Kirk, J. 1978. ‘On companions and comets’. Nature 274, 667–669.CrossRefGoogle Scholar
Kuiper, G.P. 1951. ‘On the origin of the solar system’. In Astrophysics (Hynek, J.A., ed.) pp.357–427, McGraw-Hill.Google Scholar
Lyttleton, R.A. 1974. ‘The non-existence of the Oort cometary shell’. Astrophys. Space Sci. 31, 385–401.CrossRefGoogle Scholar
Marsden, B.G. 1982. Catalogue of Cometary Orbits. Fourth Ed.Google Scholar
Marsden, B.G., and Sekanina, Z. 1973. ‘On the distribution of “original” orbits of comets of large perihelion distance’. Astron. J. 78, 1118–1124.CrossRefGoogle Scholar
Marsden, B.G., Sekanina, Z., and Everhart, E. 1978. ‘New osculating orbits for 110 comets and analysis of original orbits’. Astron. J. 83. 64–71.CrossRefGoogle Scholar
Napier, W.M., and Clube, S.V.M. 1979. ‘A theory of terrestrial catastro phism’. Nature 282, 455–459.CrossRefGoogle Scholar
Napier, W.M., and Staniucha, M. 1982. ‘Interstellar planetesimals - I. Dissipation of a primordial cloud of comets by tidal encounters with massive nebulae’. Mon. Not. Roy. Astron. Soc. 198, 723–735.CrossRefGoogle Scholar
Oja, H. 1975. ‘Perihelion distribution of near-parabolic comets’. Astron. Astrophys. 43, 317–319.Google Scholar
Oort, J.H., 1950. ‘The structure of the cloud of comets surrounding the solar system and a hypothesis concerning its origin’. Bull. Astron. Inst. Neth. 11, 91–110.Google Scholar
Öpik, E.J. 1932. ‘Note on stellar perturbations on nearly parabolic orbits’. Proc. Am. Acad. Arts Sci. 67 169–183.CrossRefGoogle Scholar
Öpik, E.J. 1973. ‘Comets and the formation of planets’. Astrophys. Space Sci. 21, 307–398.CrossRefGoogle Scholar
Radzievskii, V.V., and Tomanov, V.P., 1977. ‘On the capture of comets by the Laplace scheme’. Soviet Astron. - AJ 21, 218–223.Google Scholar
Rampino, M.R., and Stothers, R.B., 1984. ‘Terrestrial mass extinctions, cometary impacts and the Sun’s motion perpendicular to the galactic plane’. Nature 308, 709–712.CrossRefGoogle Scholar
Rickman, H. 1976. ‘Stellar perturbations of orbits of long-period comets and their significance for cometary capture’. Bull. Astron. Inst. Czech. 27, 92–105.Google Scholar
Safronov, V.S., 1969. Evolution of the Protoplanetary Cloud and Formation of the Earth and the Planets (Translated from Russian(1972) by the Israel Program for Scientific Translations, Jerusalem).Google Scholar
Safronov, V.S., 1972. ‘Ejection of bodies from the solar system in the course of the accumulation of the giant planets and the cometary cloud’. In The Motion, Evolution of Orbits, and Origin of Comets (Chebotarev, G.A., Kazimirchak-Polonskaya, E.I., and Marsden, B.G., eds.) pp.329–334, IAU Symp. No. 45.CrossRefGoogle Scholar
Sanders, D.B., Solomon, P.M., and Scoville, N.Z., 1984. ‘Giant molecular clouds in the Galaxy. I. The axisymmetric distribution of H2’. Astrophys. J. 276, 182–203.CrossRefGoogle Scholar
Sekanina, Z. 1968. ‘On the perturbation of comets by near-by stars: Encounters of comets with fast moving stars’. Bull. Astron. Inst. Czech. 19, 291–301.Google Scholar
Solomon, P.M., and Sanders, D.B., 1980. ‘Giant molecular clouds as the dominant component of interstellar matter in the Galaxy’. In Giant Molecular Clouds in the Galaxy. Third Gregynog Astrophys. Workshop (Solomon, P.M., and Edmuns, M.G., eds.) pp.47–73, Pergamon, Oxford.Google Scholar
Tyror, J.G., 1957. ‘The distribution of the directions of perihelia of long-period comets’. Mon. Not. Roy. Astron. Soc. 117, 369–379.Google Scholar
Valtonen, M.J., 1983. ‘On the capture of comets into the solar system’. Observatory 103, 1–4.Google Scholar
Valtonen, M.J., and Innanen, K.A., 1982. ‘The capture of interstellar comets’. Astrophys. J. 255, 307–315.CrossRefGoogle Scholar
Weidenschilling, S.J., 1975. ‘Close encounters of small bodies and planets’. Astron. J. 80, 145–153.CrossRefGoogle Scholar
Weissman, P.R., 1980. ‘Stellar perturbations of the cometary cloud’ Nature 288, 242–243.CrossRefGoogle Scholar
Weissman, P.R., 1982. ‘Dynamical history of the Oort cloud’. In Comets (Wilkening, L.L., ed.) pp.637–658, Univ. of Arizona Press, Tucson.CrossRefGoogle Scholar
Weissman, P.R., 1983. ‘The mass of the Oort cloud’. Astron. Astrophys. 118, 90–94.Google Scholar
Wetherill, G.W., 1975. ‘Late heavy bombardment of the Moon and terrestrial planets’. Proc. Sixth Lunar Sci. Conf. 2, 1539–1561.Google Scholar
Whitmire, D.P., and Jackson, A.A., 1984. ‘Are periodic mass extinctions driven by a distant solar companion?’. Nature 308, 713–715.CrossRefGoogle Scholar
Yabushita, S. 1972. ‘Planetary perturbation of orbits of long-period comets with large perihelion distances’. Astron. Astrophys. 16, 471–477.Google Scholar
Yabushita, S. 1979. ‘A statistical study of the evolution of the orbits of long-period comets’. Mon. Not. Roy. Astron. SOG. 187, 445–462.CrossRefGoogle Scholar
Zimbelman, J.R., 1984. ‘Planetary impact probabilities for long-period comets’. Iacrus 57, 48–54.Google Scholar