The activities of comets related to their aging and origin

  • Fred L. Whipple
Invited Papers

Abstract

Two indices have been developed for the purpose of comparing the natures of various classes of comets. The first is the Activity Index (AI), measuring the inherent magnitude increase in brightness from great solar distances to maximum near perihelion. The second, or Volatility Index (VI), measures the variation in magnitude near perihelion. Tentative determinations of these two indices are derived from observations by Max Beyer over more than 30 years for long-period (L-P) and short-period (S-P) comets near perihelion and from other homogeneous sources. AI determinations are made for 32 long-period (L-P) comets and for 14 short-period (S-P). The range of values of AI is of the order of 3 to 10 magnitudes with a median about 6. An expected strong correlation with perihelion distance q, is found to vary as ∼ q−2.3. Residuals from a least-square solution (ΔAI) are used for comparing comets of different orbital classes, the standard deviation of a single value of ΔAI is only ±1m.1 for L-P comets and ±1m.2 for S-P comets.

Among the L-P comets, 19 of period P larger than 104 years yield 〈ΔAI〉 = 0m.27 ± 0m.25 compared to 0m.39 ± 0m.26 for 13 of period between 102 years and 104 years. This denies any fading with aging among the L-P comets. Also no systematic change with period occurs for the VI index, leading to the same conclusions. Weak correlations are found with the Gas/Dust ratio of comets. No correlations are found between the two indices, nor of either index with near-perihelion magnitudes or orbital inclination.

The various data are consistent with a uniform origin for all types of comets, the nuclei being homogeneous on the large scale but quite diverse on a small scale (the order of a fraction of kilometer in extent). Small comets thus may sublimate away entirely, leaving no solid core, while huge comets may develop a less volatile core by radioactive heating and possibly become inactive like asteroids after many S-P revolutions about the Sun. When relatively new, huge comets may be quite active at great solar distances because of volatiles from the core that have refrozen in the outer layers.

Key words

Comets aging of comets activity of comets 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Bayer, M.: 1969, “Nachweis und Ergebnisse von Kometen-Beobachtungen aus den Jahren 1921–1968”, Astron. Nach., 291, 257–264.Google Scholar
  2. Beyer, M.: 1972, “Physische Beobachtungen von Kometen XVII”, Astron. Nach., 293, 241–257.Google Scholar
  3. Bobrovnikoff, N. T.: 1941, “Investigations of the Brightness of Comets, Part I”, Contr. of the Perkins Observatory, No. 15.Google Scholar
  4. Bobrovnikoff, N. T.: 1942, “Investigations of the Brightness of Comets, Part II”, Contr. of the Perkins observatory, No. 16.Google Scholar
  5. Bortle, J. E. 1991, “Post-perihelion Survival of Comets with Small q”, Inter. Comet Quart., 13, 89–91.Google Scholar
  6. Cochran, A. L. 1990, “Are all Comets Created Equal ?”, Asteroids, Comets, Meteors III, ed. C. I. Lagerkvist et al, Uppsala Univ., 281–284.Google Scholar
  7. Goldreich, P. and Ward, W. R.: 1973, “The Formation of Planetesimals”, Astrophys. J., 183, 1051–1061.Google Scholar
  8. Duncan, M., Quinn, T., and Tremaine, S.: 1987, “The Formation and Extent of the Solar System Comet Cloud”, Astrophys. J., 94, 1330–1338.Google Scholar
  9. Duncan, M., Quinn, T., and Tremaine, S.: 1988, “The Origin of Short-period Comets”, Astrophys. J., 328, L-69–73.Google Scholar
  10. Fernandez, J. A.: 1980, “On the Existence of a Comet Belt Beyond Neptune”, Mon. Not. Roy. Astr. Soc., 192, 481–491.Google Scholar
  11. Green, S. F., Meadows, A. J., and Davies, J. K.: 1985, “Infrared Observations of the Extinct cometary Candidate Minor Planet (3200) 1983TB”, Mon. Not. R. A. S., 214, 29p–36p.Google Scholar
  12. Halliday, I.: 1988, “Geminid Fireballs and the Peculiar Asteroid 3200 Phaethon”, Icarus, 76, 279–294.Google Scholar
  13. Hartmann, W. K., Tholen, D. J., and Cruikshank, D. P.: 1987, “The Relationship of Active Comets, ‘Extinct’ Comets, and Dark Asteroids”, Icarus,69, 33–50.Google Scholar
  14. Hills, J.G.: 1981, “Comet showers and the Steady-State Infall of Comets From the Oort Clouds”, Astron. J., 86, 1730–1740.Google Scholar
  15. Hills, J. G.: 1982, “The Formation of Comets by Radiation Pressure in the Outer Protosun”, Astron. J., 87, 906–910.Google Scholar
  16. Joss, P. C.: 1973, “On the origin of short-period Comets”, Astron. Astrophys., 25, 271–273.Google Scholar
  17. Kresák, L.: 1979, “Dynamical Interrelations Among Comets and Asteroids”, Asteroids, ed. T. Gehrels, Univ. Arizona Press, 289–309.Google Scholar
  18. Kuiper, G. P.: 1951, “On theOrigin of the Solar System”, Astrophysics, Ed. J. A. Hynek, McGraw-Hill, NY, 357–424.Google Scholar
  19. Meech, K. J. and Belton, M. J. S.: 1989, “(2060) Chiron”, Bur. Ast. Telegrams, IAU, No. 4770.Google Scholar
  20. Meech, K. J.: 1991, “Physical Aging in Comets”, Comets in The Post-Halley Era”, IA U colloquium 116, ed. R. L. Newburn, Jr., M. Neugebuer and J. Rahe, Kluwer Acad. Pub., 625.Google Scholar
  21. Oort, J.: 1950, “The Structure of the Cloud of Comets Surrounding the Solar System and a Hypothesis Concerning its Origin”, Bull. Astron. Netherlands, 11, 91.Google Scholar
  22. Opik, E. J.: 1963, “The Stray Bodies in the Solar System. Part 1. Survival of Cometary Nuclei and the Asteroids”, Advan. Astron. Astrophys., 2, 219–262.Google Scholar
  23. Rickman, H.: 1991, “The Thermal History and Structure of Cometary Nuclei”, Comets in to Post-Halley Era, Ed. R. L. Newburn, Jr., M. Neugebauer, J. Rahe, Kluwer Acad. Pub., 733–760.Google Scholar
  24. Sekanina, Z.: 1982, “The problem of split Comets in Review”, Comets, ed. L. L. Wilkening, Univ. Arizona, Tucson, 251–287.Google Scholar
  25. Sekanina, Z.: 1991. “Cometary Activity, Discrete Outgassing Areas, and Dust-Jet Formation”, Comets in the Post-Halley Era, Eds. R. L. Newburn, Jr., M. Neugebauer, J. Rahe, Kluwer Acad. Pub., 769–823.Google Scholar
  26. Strazzula, G. and Johnson, R. E.: 1991, “Irradiation Effects on Comets and Cometary Debris”, Comets in the Post-Halley Era, Ed. R. L. Newburn, Jr., M. Neugebauer, J. Rahe, Kluwer Acad. Pub., 243–275.Google Scholar
  27. Vsekhsvyatskii, S. K.: 1964, Physical Characteristics of Comets, Israel Prog. Sci. Translations”, Jerusalem, p20.Google Scholar
  28. Whipple, F. L.: 1950, “A comet Model. I. The Acceleration of comet Encke”, Astrophy. J., 111, 374–394.Google Scholar
  29. Whipple, F. L.: 1991, “A new Activity Index for Comets”, International Conference on Asteroids, Cornets, Meteors, in press.Google Scholar
  30. Whipple, F. L.: 1992, “A Volatility Index for Comets”, Icarus, submitted.Google Scholar
  31. Whipple, F. L. and Stefanik, R. P.: 1966, “On the Physics and Splitting of Cometary Nuclei”, Nature et Origine des Comètes, Soc. Royale des Sci. de Liege, Ser. 5, Vol. 5, 33–52.Google Scholar
  32. Yabushita, S. and Wada, K.: 1988, “Radioactive Heating and Layered Structure of Cometary Nuclei”, Earth, Moon, and Planets, 40, 303–313.Google Scholar
  33. Yamamoto, T. and Kozasa, T.: 1988, “The Cometary Nucleus as an Aggregate of Planetesimals”, Icarus, 75, 540–551.Google Scholar

Copyright information

© Kluwer Academic Publishers 1992

Authors and Affiliations

  • Fred L. Whipple
    • 1
  1. 1.Smithsonian Astrophysical ObservatoryCambridgeU.S.A.

Personalised recommendations