ON THE ELECTRON-TO-NEUTRAL NUMBER DENSITY RATIO IN THE COMA OF COMET 67P/CHURYUMOV–GERASIMENKO: GUIDING EXPRESSION AND SOURCES FOR DEVIATIONS

Journal Article · Sat Oct 10 00:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/812/1/54· OSTI ID:22518840

Vigren, E.; Eriksson, A. I.; Edberg, N. J. T.; Odelstad, E. ^[1]; Galand, M.

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1. Swedish Institute of Space Physics, Uppsala (Sweden)

We compute partial photoionization frequencies of H{sub 2}O, CO{sub 2}, and CO, the major molecules in the coma of comet 67P/Churyumov–Gerasimenko, the target comet of the ongoing ESA Rosetta mission. Values are computed from Thermosphere Ionosphere Mesosphere Energy and Dynamics/Solar EUV Experiment solar EUV spectra for 2014 August 1, 2015 March 1, and for perihelion (2015 August, as based on prediction). From the varying total photoionization frequency of H{sub 2}O, as computed from 2014 August 1 to 2015 May 20, we derive a simple analytical expression for the electron-to-neutral number density ratio as a function of cometocentric and heliocentric distance. The underlying model assumes radial movement of the coma constituents and does not account for chemical loss or the presence of electric fields. We discuss various effects/processes that can cause deviations between values from the analytical expression and actual electron-to-neutral number density ratios. The analytical expression is thus not strictly meant as predicting the actual electron-to-neutral number density ratio, but is useful in comparisons with observations as an indicator of processes at play in the cometary coma.

• OSTI ID: 22518840
• Journal Information: Astrophysical Journal, Vol. 812, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CARBON DIOXIDE
CARBON MONOXIDE
COMETS
COMPARATIVE EVALUATIONS
COSMIC ELECTRONS
ELECTRIC FIELDS
ELECTRON DENSITY
ESA
EXTREME ULTRAVIOLET RADIATION
EXTREME ULTRAVIOLET SPECTRA
IONOSPHERE
MESOSPHERE
MOLECULES
PHOTOIONIZATION
THERMOSPHERE
WATER