Pickup Ions at Comet 67P/Churyumov-Gerasimenko Measured from the Rosetta Spacecraft
Abstract
One of the most important plasma phenomena at a comet is the ion pickup process, involving the interaction of gas originating from the comet nucleus and the solar wind plasma and magnetic field. Although the pickup process can occur throughout the plasma universe, a comet allows an in situ measurement of details of the process. The comet ions are produced primarily by solar ultraviolet photoionization of the neutral molecules emitted by the comet's nucleus as it approaches the Sun. In the case of comet 67P/Churyumov-Gerasimenko these molecules were measured to have velocities <1 km/s ( 0.1 eV for water ions) when emitted. Such ions produced near the spacecraft can be attracted to a negatively charged surface and be detected. In fact, both the Ion and Electron Sensor (IES) and the Ion Composition Analyzer (ICA) on board Rosetta did measure these very low energy ions. However, if the ionization takes place after the molecule has traveled some distance, the newborn ion will feel the qv x B force of the IMF and begin gyrating about this field, having been "picked up" by the motion of the solar wind (SW) and IMF. Depending on the initial angle between the ion and SW direction, the ion could increase its velocity to a maximum of twice the SW speed, to 800 km/s typically, or an energy of 60 keV for a water ion. In addition to measuring very low energy ions, IES also measured 17 keV ions we believe are pickup heavy ions produced far away from the comet, and brought back to the comet by the SW. We present details of the ion pickup process as measured by IES and ICA during the 2 years Rosetta was near comet 67P.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSH12B..07G
- Keywords:
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- 2124 Heliopause and solar wind termination;
- INTERPLANETARY PHYSICSDE: 2126 Heliosphere/interstellar medium interactions;
- INTERPLANETARY PHYSICSDE: 2152 Pickup ions;
- INTERPLANETARY PHYSICSDE: 7845 Particle acceleration;
- SPACE PLASMA PHYSICS