| Autor: |
Moeslinger, A., Nilsson, H., Stenberg Wieser, G., Gunell, H., Goetz, C. |
| Předmět: |
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| Zdroj: |
Journal of Geophysical Research. Space Physics; Sep2023, Vol. 128 Issue 9, p1-15, 15p |
| Abstrakt: |
No spacecraft visiting a comet has been equipped with instruments to directly measure the static electric field. However, the electric field can occasionally be estimated indirectly by observing its effects on the ion velocity distribution. We present such observations made by the Rosetta spacecraft on 19 April 2016, 35 km from the nucleus. At this time comet 67P was at a low outgassing rate and the plasma environment was relatively stable. The ion velocity distributions show the cometary ions on the first half of their gyration. We estimate the bulk drift velocity and the gyration speed from the distributions. By using the local measured magnetic field and assuming an E × B drift of the gyrocentre, we get an estimate for the average electric field driving this ion motion. We analyze a period of 13 hr, during which the plasma environment does not change drastically. We find that the average strength of the perpendicular electric field component is 0.21 mV/m. The direction of the electric field is mostly anti‐sunward. This is in agreement with previous results based on different methods. Plain Language Summary: Measuring the static electric field in space plasmas is difficult. Most spacecraft do not have dedicated instruments for it, and the Rosetta mission to comet 67P is no exception. But the electric field is one of the main governing factors behind the motion of newly born cometary ions. In this study, we use measurements of the cometary ions to estimate the average electric field close to the nucleus. The observations are made on the 19 April 2016 by the Ion Composition Analyzer, which measures the energy and travel direction of the different plasma species. The specific shape of the observed velocity distribution of cometary ions—a partial ring—indicates that the fields accelerating the observed cometary ions are relatively homogeneous. The spatial scale this applies to is approximately one gyroradius, which we estimated to be around 340 km. The resulting electric field is 0.21 mV/m, which is significantly smaller than the expected field in the upstream solar wind, far away from the nucleus. Key Points: Rosetta observations show partial ring distributions of cometary ions at comet 67P close to the nucleusFrom the velocity distributions the plasma bulk velocity and gyration speed are determinedWe estimate the perpendicular electric field component from the bulk velocity and find a mostly anti‐sunward field of 0.21 mV/m [ABSTRACT FROM AUTHOR] |
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Complementary Index |
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