Advertisement

Irradiation Effects on Comets and Cometary Debris

  • G. Strazzulla
  • R. E. Johnson
Part of the Astrophysics and Space Science Library book series (ASSL, volume 167)

Abstract

For the last 10 years, many experimental results have been obtained on the chemical and physical changes induced by ion and electron irradiation of materials relevant to comets. Those results are reviewed here, together with their physical interpretation and their relevance for cometary astrophysics. Cometary material is, from the time of its origin, altered by the large amount of energy deposited by energetic ions. Four phases of the irradiation history are considered: the pre-cometary phase, during which interstellar dust is bombarded by cosmic-ray ions; the accretion phase, during which comets are built up, possibly in an environment rich in fast ions (T-Tau phase); the cometary phase, during which the outer layers of the comets are irradiated by galactic ions in the Oort cloud; and the post-cometary phase, during which dust, lost from the comet, is bombarded by solar ions.

The relevant applications of laboratory results are reviewed. In particular, the ability of ion irradiation of simple carbon-containing ices to produce complex refractory organic materials is discussed. In the Oort cloud, this process can occur several meters into the surface, so that the buildup of a stable organic crust may occur. A comparison of ion irradiation at various stages is also made with other models for the production of organics.

Keywords

Solar Wind Solar System Cometary Nucleus Interstellar Dust Oort Cloud 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Allen, D.A., and Wickramasinghe, D.T. (1987). ‘Discovery of organic grains in comet Wilson’. Nature 329, 615–616.ADSCrossRefGoogle Scholar
  2. Andersen, H.H., and Bay, H.L. (1981). ‘Sputtering yield measurements’. In Sputtering by Particle Bombardment I, R. Behrisch (ed.), Springer-Verlag, Berlin, pp. 145–218.CrossRefGoogle Scholar
  3. Andronico, G., Baratta, G.A., Spinella, F., and Strazzulla, G. (1987). ‘Optical evolution of laboratory-produced organics: Applications to Phoebe, Iapetus, outer belt asteroids and cometary nuclei’. Astron. Astrophys. 184, 333–336.ADSGoogle Scholar
  4. Baas, F., Geballe, T.R., and Walther, D.M. (1986). ‘Spectroscopy of the 3.4 micron emission feature in comet Halley’. Astrophys. J. Lett. 311, L97–L101.ADSCrossRefGoogle Scholar
  5. Betz, G., and Wehner, G.K. (1983). ‘Sputtering of multicomponent materials’. In Sputtering by Particle Bombardment II, R. Behrisch (ed.), Springer-Verlag, Berlin, pp. 11–90.CrossRefGoogle Scholar
  6. Boring, J.W., Nansheng, Z., Chrisey, D.B., O’Shaughnessey, D.J., Phipps, J.A., and Johnson, R.E. (1985). ‘The production of S2 by keV ion bombardment’. In Asteroids, Comets and Meteors II, C.I. Lagerkvist, B.A. Lindblad, H. Lundstedt, and H. Rickman (eds.), University of Uppsala Press, Uppsala, pp. 229–234.Google Scholar
  7. Bradley, J.P., Brownlee, D.E., and Fraundorf, P. (1984). ‘Discovery of nuclear tracks in interplanetary dust’. Science 226, 1432–1434.ADSCrossRefGoogle Scholar
  8. Bregman, J.D., et al. (1987). ‘Airborne and ground based spectrophotometry of comet P/Halley from 5–13 micrometers’. Astron. Astrophys, 187, 616–620.ADSGoogle Scholar
  9. Brown, W.L., and Johnson, R.E. (1986). ‘Sputtering of ices: A review’. Nucl. Instr. and Meth. B13, 295–303.ADSGoogle Scholar
  10. Brown, W.L., Augustyniak, W.M., Lanzerotti, L.J., Johnson, R.E., and Evatt, R. (1980). ‘Linear and non linear processes in the erosion of H2O ice by fast light ions’. Phys. Rev. Lett. 45, 1632–1635.ADSCrossRefGoogle Scholar
  11. Brown, W.L., Lanzerotti, L.J., and Johnson, R.E. (1982a). ‘Fast ion bombardment of ices and its astrophysical implications’. Science 218, 525–531.ADSCrossRefGoogle Scholar
  12. Brown, W.L., Augustyniak, W.M., Simmons, E., Marcantonio, K.J., Lanzerotti, L.J., Johnson, R.E., Boring, J.W., Reimann, C.T., Foti, G., and Pirronello, V. (1982b). ‘Erosion and molecular formation in condensed gas films by electronic energy loss of fast ions’. Nucl. Instr. Methods 198, 1–8.Google Scholar
  13. Brown, W.L., Foti, G., Lanzerotti, L.J., Bower, J.E., and Johnson R.E. (1987). ‘Delayed emission of hydrogen from ion bombardment of solid methane’. Nucl. Instr. Methods B19/20, 899–902.Google Scholar
  14. Chrisey, D.B., Boring, J.W., Johnson, R.E., and Phipps, J.A. (1988). ‘Molecular ejection from low temperature sulfur by keV ions’. Surf. Sci. 195, 594–618.ADSCrossRefGoogle Scholar
  15. Chrisey, D.B., Brown, W.L., and Boring J.W. (1989). ‘Electronic excitation of condensed CO: Sputtering and chemical change’. Surf. Sci., in press.Google Scholar
  16. Chyba, C., and Sagan, C. (1987). ‘Infrared emission by organic grains in the coma of comet Halley’. Nature 330, 350–353.ADSCrossRefGoogle Scholar
  17. Chyba, C., and Sagan, C. (1988). ‘Cometary organic matter still a contentious issue’. Nature 332, 592.ADSCrossRefGoogle Scholar
  18. Combes, M., et al. (1986). ‘Infrared sounding of comet Halley from Vega 1’. Nature 321, 266–268.ADSCrossRefGoogle Scholar
  19. Combi, M.R. (1987). ‘Sources of cometary radicals and their jets: Gases or grains’. Icarus 71, 178–191.ADSCrossRefGoogle Scholar
  20. Cosmovici, C., and Ortolani, S. (1984). ‘Detection of new molecules in the visible spectrum of comet IRAS-Araki-Alcock (1984)’. Nature 310, 122–124.ADSCrossRefGoogle Scholar
  21. de Jong, T., and Kamijo F., (1973). ‘Growth and destruction of interstellar grains in the presence of low-energy cosmic rays’. Astron. Astrophys. 25, 363–370.ADSGoogle Scholar
  22. Donn, B. (1976). ‘The nucleus: Panel discussion’. In The Study of Comets, B. Donn et al. (eds.), NASA SP-393, pp. 611–621.Google Scholar
  23. Donn, B., and Hughes, D. (1986). ‘A fractal model of a cometary nucleus formed by random accretion’. ESA SP-250, vol. III, pp. 523–524.Google Scholar
  24. Draganic, I.G., Draganic, Z.D., and Vujosevic, S.I. (1984). ‘Some radiation-chemical aspects of chemistry in cometary nuclei’. Icarus 60, 464–475.ADSCrossRefGoogle Scholar
  25. Fechtig, H., and Mukai, T. (1985). ‘Dust of variable porosities (densities) in the Solar System’. In Ices in the Solar System, J. Klinger et al. (eds.), D. Reidel Publ. Co., Dordrecht, pp. 251–259.CrossRefGoogle Scholar
  26. Feigelson, E.D. (1982). ‘X-ray emission from young stars and implications for the early Solar System’. Icarus 51, 155–163.ADSCrossRefGoogle Scholar
  27. Field, G.B., Goldsmith, D.W., and Habing, H.J. (1969). ‘Cosmic-ray heating of interstellar gas’. Astrophys. J. Lett. 155, L149–L154.ADSCrossRefGoogle Scholar
  28. Foti, G., Calcagno, L., Sheng, K.L., and Strazzulla, G. (1984). ‘Micrometre-sized polymer layers synthesized by MeV ions impinging on frozen methane’. Nature 310, 126–128.ADSCrossRefGoogle Scholar
  29. Foti, G., Calcagno, L., Zhu, F.Z., and Strazzulla, G. (1987). ‘Chemical evolution of solid methane by keV ion bombardment’. Nucl. Instr. Methods in Phys. Res. B24–25, 522–525.CrossRefGoogle Scholar
  30. Gombosi, T.I., and Houpis, H.L.F. (1986). ‘An icy-glue model of cometary nuclei’. Nature 324, 43–44.ADSCrossRefGoogle Scholar
  31. Greenberg, J.M. (1982). ‘What are comets made of? A model based on interstellar dust’. In Comets, L.L. Wilkening (ed.), University of Arizona Press, Tucson, pp. 131–163.Google Scholar
  32. Greenberg, J.M., and Zhao, N. (1988). ‘Cometary organics’. Nature 331, 124.ADSCrossRefGoogle Scholar
  33. Hanner, M.S., Knacke, R., Sekanina, Z., and Tokunaga, A.T. (1985). ‘Dark grains in comet Crommelin’. Astron. Astrophys. 152, 177–181.ADSGoogle Scholar
  34. Haring, R.A., Haring A., Klein, F.S., Kummel, A.C., and de Vries, A.E. (1983). ‘Reactive sputtering of simple condensed gases by keV heavy ion bombardment’. Nucl. Instrum. Methods 211, 529–538.CrossRefGoogle Scholar
  35. Harris, A.W. (1978). ‘Dynamics of planetesimals formation and planetary accretion’. In the Origin of the Solar System, S.F. Dermott (ed.), Wiley, New York, pp. 469–492.Google Scholar
  36. Hart, E.J., and Platzman, R.L. (1961). ‘Radiation chemistry’ In Physical Mechanisms in Radiation Biology 1, Academic Press, New York, pp. 93–120.Google Scholar
  37. Hoyle, F., and Wickramasinghe, N.C. (1985). Living Comets. University College Press, London.Google Scholar
  38. Hoyle, F., and Wickramasinghe, N.C. (1987). ‘Organic dust in comet Halley’. Nature 328, 117.ADSCrossRefGoogle Scholar
  39. Huebner, W.F. (1987). ‘First polymer in space identified in Comet Halley’. Science 237, 628–630.ADSCrossRefGoogle Scholar
  40. Jessberger, E.K., Cristoforidis, A., and Kissel, J. (1988). ‘Aspects of the major element composition of Halley’s dust’. Nature 332, 691–695.ADSCrossRefGoogle Scholar
  41. Johnson, R.E. (1985). ‘Comment on the evolution of interplanetary grains’. In Ices in the Solar System, J. Klinger et al. (eds.), D. Reidel Publ. Co., Dordrecht, pp. 337–339.CrossRefGoogle Scholar
  42. Johnson, R.E. (1989a). Energetic Charged-Particle Interactions With Atmospheres and Surfaces. Springer-Verlag, Berlin, in press.Google Scholar
  43. Johnson, R.E. (1989b). ‘Laboratory simulations: The primordial comet mantle’. In the NASA publication for the Comet Sample Return Conference, Milipitas, 1989, in press.Google Scholar
  44. Johnson, R.E., and Lanzerotti, L.J. (1986). ‘Ion bombardment of interplanetary dust’. Icarus 66, 619–624.ADSCrossRefGoogle Scholar
  45. Johnson, R.E., Lanzerotti, L.J., Brown, W.L., Augustyniak, W.M., and Mussil, C. (1983). ‘Charged particle erosion of frozen volatiles in ice grains and comets’. Astron. Astrophys. 123, 343–346.ADSGoogle Scholar
  46. Johnson, R.E., Lanzerotti, L.J., and Brown, W.L. (1984). ‘Sputtering processes: Erosion and chemical change’. Adv. Space Res. 4, 41–51.ADSCrossRefGoogle Scholar
  47. Johnson, R.E., Barton, L.A., Boring, J.W., Jesser, W.A., Brown, W.L., and Lanzerotti, L.J. (1985). ‘Charged particle modification of ices in the Jovian and Saturnian systems’. In Ices in the Solar System, J. Klinger et al. (eds.), D. Reidel Publ. Co., Dordrecht, pp. 301–316.CrossRefGoogle Scholar
  48. Johnson, R.E., Cooper, J.F., Lanzerotti, L.J., and Strazzulla, G. (1987). ‘Radiation formation of a non-volatile comet crust’. Astron. Astrophys. 187, 889–892.ADSGoogle Scholar
  49. Jull, A.J.T., Wilson, G.C., Long, J.V.P., Reed, S.J.B., and Pillinger, C.T. (1980). ‘Sputtering rates of minerals and implications for abundances of solar elements in lunar samples’. Nucl. Instr. Methods 168, 357–365.CrossRefGoogle Scholar
  50. Khare, B.N., Sagan, C., Arakawa, E.T., Suits, F., Calcott, T.A., and Williams, M.W. (1984). ‘Optical constants of organic tholins produced in a simulated Titanian atmosphere from X-ray to microwave frequencies’. Icarus 60, 127–137.ADSCrossRefGoogle Scholar
  51. Kissel, J., and Krueger, F.R. (1987a). ‘The organic component in dust from comet Halley as measured by the PUMA mass spectrometer on board Vega 1’. Nature 326, 755–760.ADSCrossRefGoogle Scholar
  52. Kissel, J., and Krueger, F.R. (1987b). ‘Organic dust in comet Halley’. Nature 328, 117.ADSCrossRefGoogle Scholar
  53. Kissel, J., et al. (1986a). ‘Composition of comet Halley dust particles from Vega observations’. Nature 321, 280–282.ADSCrossRefGoogle Scholar
  54. Kissel, J., et al. (1986b). ‘Composition of comet Halley dust particles from Giotto observations’. Nature 321, 336–337ADSCrossRefGoogle Scholar
  55. Knacke, R.F., Brooke, T.Y., and Joyce, R.R. (1987). ‘The 3.2–3.6 µm emission features in comet P/Halley: Spectral identification and similarities’. Astron. Astrophys. 187, 625–628.ADSGoogle Scholar
  56. Lanzerotti, L.J., Brown, W.L., Poate, C.M., and Augustyniak, W.M. (1978). ‘Low energy cosmic ray erosion of ice grains in interplanetary and interstellar media’. Nature 272, 431–433.ADSCrossRefGoogle Scholar
  57. Lanzerotti, L.J., Brown, W.L., and Johnson, R.E. (1985). ‘Laboratory studies of ion irradiation of water, sulfur dioxide, and methane ices’. In Ices in the Solar System, J. Klinger et al. (eds.), D. Reidel Publ. Co., Dordrecht, pp. 317–333.CrossRefGoogle Scholar
  58. Lanzerotti, L.J., Brown, W.L., and Marcantonio, K.J. (1987). ‘Experimental study of erosion of methane ice by energetic ions and some considerations for astrophysics’. Astrophys. J. 313, 910–922.ADSCrossRefGoogle Scholar
  59. Leger, A., Jura, M., and Amont, A. (1985). ‘Desorption from interstellar grains’. Astron. Astrophys. 144, 147–160.ADSGoogle Scholar
  60. Le Sergeant d’Hendecourt, L.B., and Lamy, Ph. L. (1980). ‘On the size distribution and physical properties of interplanetary dust grains’. Icarus 43, 350–372.ADSCrossRefGoogle Scholar
  61. Littmark, U., and Ziegler, J.F. (1980). Handbook of Range Distributions for Energetic Ions in All Elements. Pergamon, Elmsford, New York.Google Scholar
  62. Mazzoldi, P., and Arnold, G.W. (1987). Ion Beam Modification of Insulators. Elsevier, Amsterdam.Google Scholar
  63. Melcher, C.L., LePoire, D.J., Cooper, B.H., and Trombello, T.A. (1982). ‘Erosion of frozen sulfur dioxide by ion bombardment: Application to Io’. Geophys. Res. Lett. 9, 1151–1154.ADSCrossRefGoogle Scholar
  64. Mitchell, D.L. et al. (1987). ‘Evidence for chain molecules enriched in carbon, hydrogen and oxygen in comet Halley’. Science 237, 626–628.ADSCrossRefGoogle Scholar
  65. Moore, M.H. (1982). ‘Studies of proton-irradiated cometary-type ice mixtures’. Ph.D. thesis, University of Maryland, College Park, Maryland.Google Scholar
  66. Moore, M.H., and Donn, B. (1982). ‘The infrared spectrum of a laboratory synthesized residue: Implication for the 3.4 µm interstellar absorption feature’. Astrophys. J. 257, L47–L50.ADSCrossRefGoogle Scholar
  67. Moore, M.H., Donn, B., Khanna, R., and A’Hearn, M.F. (1983). ‘Studies of protonirradiated cometary-type ice mixtures’. Icarus 54, 388–405.ADSCrossRefGoogle Scholar
  68. Moroz, V.I., et al. (1987). ‘Detection of parent molecules in comet P/Halley from IKS-Vega experiment’. Astron. Astrophys. 187, 513–518.ADSGoogle Scholar
  69. Mukai, T., and Schwehm, G. (1981). ‘Interaction of grains with the solar energetic particles’. Astron. Astrophys. 95, 373–382.ADSGoogle Scholar
  70. Mumma, M.J., Blass, W.E., Weaver, H.A., and Larson, H.P. (1989). ‘Measurements of the ortho-para ratio and the nuclear spin temperatures of water vapour in comet Halley and Wilson (1986i) and the implication for their origin and evolution’. Submitted.Google Scholar
  71. O’Shaughnessy, D.J., Boring, J.W., Philipps, J.A., Johnson, R.E., and Brown, W.L. (1986). ‘Sputtering of rare gas solids by keV ions’. Nucl. Instr. and Meth. B13, 304–308.ADSGoogle Scholar
  72. Pirronello, V., and Lanzafame, G. (1989). ‘Molecules synthesized by cosmic rays in cometary nuclei: A tool to estimate their low energy spectrum’. Astrophys. J., in press.Google Scholar
  73. Pirronello, V., Brown, W.L., Lanzerotti, L.J., Marcantonio, K.J., and Simmons, E. (1982). ‘Formaldehyde formation in a H2O/CO2 ice mixture under irradiation by fast ions’. Astrophys. J. 262, 636–640.ADSCrossRefGoogle Scholar
  74. Pirronello, V., Strazzulla, G., Foti, G., Brown, W.L., and Lanzerotti, L.J. (1984). ‘Formaldehyde formation in cometary nuclei’. Astron. Astrophys. 134, 204–206.ADSGoogle Scholar
  75. Prialnik, D., and Bar-Nun, A. (1988). ‘The formation of a permanent dust mantle and its effect on cometary activity’. Icarus 74, 272–283.ADSCrossRefGoogle Scholar
  76. Reimann, C.T., Boring, J.W., Johnson, R.E., Garret, J.W., Farmer, K.R. and Brown, W.L. (1984). ‘Ion-induced molecular ejection from D2O ice’. Surf. Sci. 147, 227–240.ADSCrossRefGoogle Scholar
  77. Rickman, H. (1986). ‘Masses and densities of comets Halley and Kopff’. In The Comet Nucleus Sample Return Mission, ESA SP-249, pp. 195–205.Google Scholar
  78. Rickman, H. (1987). ‘Physical evolution of comets’. In Proc. 10th European Astronomy Meeting of the IAU, Prague 1987.Google Scholar
  79. Rickman, H., and Fernandez, J.A. (1986). ‘Formation and blowoff of a cometary dust mantle’. In The Comet Nucleus Sample Return Mission, ESA SP-249, pp. 185–195.Google Scholar
  80. Ryan, M.P., Jr., and Draganic, I.G. (1986). ‘An estimate of the contribution of high energy cosmic-ray protons to the absorbed dose inventory of a cometary nucleus’. Astrophys. Space. Sci. 125, 49–68.ADSCrossRefGoogle Scholar
  81. Sack, N., Schuster, R., Hoffman, A., and Schneider, H.J. (1988). ‘Production of amines by proton bombardment of simple condensed gases’. Icarus 76, 110–117.ADSCrossRefGoogle Scholar
  82. Sagdaeev, R.Z., Elyasberg, P.E., and Moroz, V.I. (1988). ‘Is the nucleus of comet Halley a low density body?’ Nature 331, 240–242.ADSCrossRefGoogle Scholar
  83. Stern, S.A. (1988). ‘Collisions in the Oort cloud’. Icarus 73, 499–507.ADSCrossRefGoogle Scholar
  84. Stern, S.A., and Shull, M.J. (1988). ‘The relevance of supernovas and passing stars on comets’. Nature 332, 407–411.ADSCrossRefGoogle Scholar
  85. Strazzulla, G. (1985). ‘Modifications of grains by particle bombardment in the early Solar System’. Icarus 61, 48–56.ADSCrossRefGoogle Scholar
  86. Strazzulla, G. (1986). ‘“Primitive” galactic dust in the Solar System?’ Icarus 67, 63–70.ADSCrossRefGoogle Scholar
  87. Strazzulla, G. (1988). ‘Ion bombardment: Techniques, materials and applications’. In Experiments on Cosmic Dust Analogues, E. Bussoletti et al. (eds.), Kluwer Acad. Publ., Dordrecht, pp. 103–113.CrossRefGoogle Scholar
  88. Strazzulla, G., Calcagno, L., and Foti, G. (1983a). ‘Polymerization induced on interstellar grains by low energy cosmic rays’. M.N.R.A.S. 204, 59p–62p.ADSGoogle Scholar
  89. Strazzulla, G., Pirronello, V., and Foti, G. (1983b). ‘Physical and chemical effects induced by energetic ions on comets’. Astron. Astrophys. 123, 93–97.ADSGoogle Scholar
  90. Strazzulla, G., Calcagno, L., and Foti, G. (1984). ‘Build up of carbonaceous material by fast protons on Pluto and Triton’. Astron. Astrophys. 140, 441–444.ADSGoogle Scholar
  91. Strazzulla, G., Calcagno, L., Foti, G., and Sheng, K.L. (1985). ‘Interaction between solar energetic particles and interplanetary grains’. In Ices in the Solar System, J. Klinger et al. (eds.), D. Reidel Publ. Co., Dordrecht, pp. 73–285.Google Scholar
  92. Strazzulla, G., Torrisi, L., and Foti, G. (1988). ‘Light scattering from ion irradiated frozen gases’. Europhys Lett. 7(5), 431–434.ADSCrossRefGoogle Scholar
  93. Tokunaga, A.T., Nagata, T., and Smith, R.G. (1987). ‘Detection of a new emission band at 2.8µm in comet P/Halley’. Astron. Astrophys. 187, 519–522.ADSGoogle Scholar
  94. Torrisi, L., Coffa, S., Foti, G., and Strazzulla, G. (1986). ‘Sulphur erosion by 1.0 MeV helium ions’. Radiation Eff. 100, 61–69CrossRefGoogle Scholar
  95. Torrisi, L., Coffa, S., Foti, G., Johnson, R.E., Chrisey, D.B., and Boring, J.W. (1988). ‘Threshold dependence in the electronic sputtering of condensed sulfur’. Phys. Rev. B 38, 1516–1519.ADSCrossRefGoogle Scholar
  96. Vanysek, M.K., and Wickramasinghe, N.C. (1975). ‘Formaldehyde polymers in comets’. Astrophys. Space Sci. 33, L19–L28.ADSGoogle Scholar
  97. Watson, W.D. (1975). ‘Physical processes for the formation and destruction of interstellar molecules’. In Atomic and Molecular Physics and the Interstellar Matter, R. Balian et al. (eds.), North Holland Publ. Co., Amsterdam, pp. 177–271.Google Scholar
  98. Weissman, P.R. (1986). ‘Are cometary nuclei primordial rubble piles?’ Nature 320, 242–244.ADSCrossRefGoogle Scholar
  99. Whipple, F.L. (1950). ‘A comet model: The acceleration of comet Encke’. Astrophys. J. 111, 375–394.ADSCrossRefGoogle Scholar
  100. Whipple, F.L. (1972). ‘The origin of comets’. In The Motion, Evolution of Orbits and Origin of Comets, IAU Symp. 45, D. Reidel Publ. Co., Dordrecht, pp. 401–408.CrossRefGoogle Scholar
  101. Whipple, F.L. (1977). ‘The constitution of cometary nuclei’. In Comets, Asteroids, Meteorites: Interrelations, Evolution and Origins, A.H. Delsemme (ed.), University of Toledo, Toledo, Ohio, pp. 25–32.Google Scholar
  102. Wickramasinghe, D.T., and Allen, D.A. (1986). ‘Discovery of organic grains in comet Halley’. Nature 323, 44–46.ADSCrossRefGoogle Scholar
  103. Wood, J.A. (1986). ‘Comet nucleus models: A review’. In The Comet Nucleus Sample Return Mission, ESA SP-249, pp. 123–131.Google Scholar
  104. Worden, S.P., Schneeberger, T.J., Kuhn, J.R., and Africano, J.L. (1981). ‘Flare activity of T Tauri stars’. Astrophys. J. 244, 520–527.ADSCrossRefGoogle Scholar
  105. Yamamoto, T., Nakagawa, N., and Fukui, Y. (1983). ‘The chemical composition and thermal history of the ice of a cometary nucleus’. Astron. Astrophys. 122, 171–176.ADSGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 1991

Authors and Affiliations

  • G. Strazzulla
    • 1
  • R. E. Johnson
    • 2
  1. 1.Istituto di AstronomiaCitta’ UniversitariaCataniaItaly
  2. 2.Dept. of Engineering and Engineering PhysicsUniversity of VirginiaCharlottesvilleUSA

Personalised recommendations