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Rosetta Observations of Plasma and Dust at Comet 67P [Elektronisk resurs]

Johansson, Fredrik Leffe, 1988- (författare)
Eriksson, Anders (preses)
Wahlund, Jan-Erik (preses)
André, Nicolas (opponent)
Uppsala universitet Teknisk-naturvetenskapliga vetenskapsområdet (utgivare)
Uppsala universitet Teknisk-naturvetenskapliga vetenskapsområdet (utgivare)
Publicerad: Uppsala : Acta Universitatis Upsaliensis, 2020
Engelska 35
Serie: Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, 1651-6214 1651-6214 ; 1989
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  • E-bokAvhandling(Diss. (sammanfattning) Uppsala : Uppsala universitet, 2020)
Sammanfattning Ämnesord
  • In-situ observations of cometary plasma are not made because they are easy. The historic ESA Rosetta mission was launched in 2004 and traversed space for ten years before arriving at comet 67P/Churyumov-Gerasimenko, which it studied in unprecedented detail for two years. For the Rosetta Dual Langmuir Probe Experiment (LAP), the challenge was increased by the sensors being situated on short booms near a significantly negatively charged spacecraft, which deflects low-energy charged particles away from our instrument. To disentangle the cometary plasma signature in our signal, we create a charging model for the particular design of the Rosetta spacecraft through 3D Particle-in-Cell/hybrid spacecraft-plasma interaction simulations, which also can be applicable to similarly designed spacecraft in cold plasma environments. By virtue of this model, we find a way to cross-calibrate (with the Mutual Impedance probe, MIP) the LAP spacecraft potential to a plasma density estimate with increased temporal resolution and dynamic range than any single plasma instrument alone. To characterise and disentangle the Sun-driven photoelectric current from the positive cometary ion current signal, using three different methods (where we believe one is novel), we find a signature of an attenuation of the Extreme Ultraviolet (EUV) radiation from the Sun that follows the cometary out-gassing activity. We discuss possible reasons for this, where the scattering and absorption of radiation by ~20 nm sized dust grains created by the disintegration of far larger cometary dust grains far from the nucleus appears most likely. By cross-calibrating also our current measurements to MIP, we find a cometary ion speed estimate, which, when applied to a simple comet ionosphere model using the LAP photoemission as a photoionisation proxy, predicts the measured comet plasma densities near perihelion, when comet activity was highest. This demonstrates that the LAP cross-calibration estimates are self-consistent, but also strongly suggests that the EUV attenuation we reported is apparent also in the comet ionosphere, as less plasma is ionised by EUV radiation. The ion speed estimates from LAP are consistent with recent results of cometary water ion velocities from the Ion Composition Analyser (ICA), and much elevated above the comet neutral speed, often by a factor of 5. This verifies that the cometary ions are not collisionally coupled to the neutrals, and instead rapidly accelerated by some electric field, such as an ambipolar electric field or from plasma wave activity. 


Natural Sciences  (hsv)
Physical Sciences  (hsv)
Fusion, Plasma and Space Physics  (hsv)
Naturvetenskap  (hsv)
Fysik  (hsv)
Fusion, plasma och rymdfysik  (hsv)
Fysik med inriktning mot rymd- och plasmafysik  (uu)
Physics with specialization in Space and Plasma Physics  (uu)


government publication  (marcgt)

Indexterm och SAB-rubrik

Langmuir Probes
Spacecraft-plasma interaction
Electrostatic Probes
rymdfarkost-plasma växelverkan
Inställningar Hjälp

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