Measurements of Low Energy Electrons and Spacecraft Potentials Near Comet p/ Halley

Details Measurements of Low Energy Electrons and Spacecraft Potentials Near Comet p/ Halley Measurements of Low Energy Electrons and Spacecraft Potentials Near Comet p/ Halley

Nov 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987a%26a...187..297p&link_type=abstract

Astronomy and Astrophysics, Vol.187, NO. 1+2/NOV, P. 297, 1987

Astronomy and Astrophysics

Astrophysics

14

Scientific paper

Data collected with the Langmuir probes and the electric field sensors on Vega-1 and Vega-2 show that the spacecraft potentials were a few volts positive in the outer coma and less positive near the closest approach. This leads to the conclusion that the energy of the secondary electrons generated by gas and dust impacts was lower than assumed in previous model work. The electron density in the outer coma were of the order 50 cm-3 for Vega-1 and 25 cm-3 for Vega-2 with wavelike fluctuations over a time interval of 10 min, or a distance of 500,000 km. Steep increases of the electron density were observed at a distance of 150,000 km from the nucleus, in the vicinity of the cometopause. Langmuir probe data are judged to suffer little influence from gas and dust impacts at distances larger than 50,000 km where the electron densities for both flights were of the order of 103 cm-3. The electron mean kinetic energy was typically 0.5 eV for both flights, a slight increase was observed by Vega-1 within 150,000 km. Asymmetries between the potentials of two electric field probes, measured relative to the spacecraft, are thought to result from small dust impacts. Such asymmetries are characterized by a gradual increase (Vega-1) or a clear onset (Vega-2) at distances of about 80,000 km; a strong enhancement of this effect was also seen on Vega-2 at distances less than 10,000 km from the nucleus.

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