Earth, Moon, and Planets

, Volume 60, Issue 1, pp 59–68 | Cite as

Representative abundances of a few positive ions in the innermost coma of comet Halley

  • P. P. Saxena
  • Alka Misra


The production rate of H2O molecules at a heliocentric distance of 1 AU for comet Halley and the abundance ratio with respect to water (H2O) of parent molecules at the cometary nucleus from the paper of Yamamoto (1987) have been used to compute the number densities of positive ions viz. H3O+, H3S+, H2CN+, H3CO+, CH3OH 2 + and NH 4 + at various cometocentric distances within 600 kms from the nucleus.

The role of proton transfer reactions in producing major ionic species is discussed. A major finding of the present investigation is that NH 4 + ion which may be produced through proton transfer reactions is the most abundant ion near the nucleus of a comet unless the abundance of NH3 as a parent is abnormally low. Using the quoted value of Q(NH3)/Q(H2O) for comet Halley and the life times of NH3 and H2O molecules, the abundance ratio N(NH3)/N(H2O) is found to be one-third of that used in the present paper. The consequent proportionate decrease in the NH 4 + ions does not, however, affect its superiority in number density over other ions near the nucleus.

The number density of the next most abundant ion viz. H3O+ is found to be 4 × 104 cm-3 at the nucleus of comet Halley and decreases by a factor of two only upto a distance of 600 K ms from the nucleus. The ionic mass peak recorded by VEGA and GIOTTO spacecrafts atm/q = 18 is most probably composite of the minor ionic species H2O+, as its number density = 102 cm-3 remains virtually constant in the inner coma and of NH 4 + , the number density of which at large cometocentric distances may add to the recorded peak atmlq = 18. The number densities of other major ions produced through proton transfer from H3O+ are also discussed in the region within 600 K ms from the nucleus of comet Halley.


Proton Transfer Ionic Species Mass Peak Heliocentric Distance Abundance Ratio 
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Copyright information

© Kluwer Academic Publishers 1993

Authors and Affiliations

  • P. P. Saxena
    • 1
  • Alka Misra
    • 1
  1. 1.Department of Mathematics and AstronomyLucknow UniversityLucknowIndia

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