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  • Eriksson, Anders I.Uppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen (author)

Cold and warm electrons at comet 67P/Churyumov-Gerasimenko

  • Article/chapterEnglish2017

Publisher, publication year, extent ...

  • 2017-05-24
  • EDP SCIENCES S A,2017
  • printrdacarrier

Numbers

  • LIBRIS-ID:oai:DiVA.org:kth-217060
  • https://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-217060URI
  • https://doi.org/10.1051/0004-6361/201630159DOI
  • https://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-337755URI

Supplementary language notes

  • Language:English
  • Summary in:English

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  • Subject category:ref swepub-contenttype
  • Subject category:art swepub-publicationtype

Notes

  • QC 20171123
  • Funding: The results presented here are only possible thanks to the combined efforts over 20 yr by many groups and individuals involved in Rosetta, including but not restricted to the ESA project teams at ESTEC, ESOC and ESAC and all people involved in designing, building, testing and operating RPC and LAP. We thank Kathrin Altwegg for discussions of the pulses in LAP and COPS. Rosetta is a European Space Agency (ESA) mission with contributions from its member states and the National Aeronautics and Space Administration (NASA). The work on RPC-LAP data was funded by the Swedish National Space Board under contracts 109/12, 171/12, 135/13, 166/14 and 168/15, and by Vetenskapsradet under contract 621-2013-4191. This work has made use of the AMDA and RPC Quicklook database, provided by a collaboration between the Centre de Donnees de la Physique des Plasmas CDPP (supported by CNRS, CNES, Observatoire de Paris and Universite Paul Sabatier, Toulouse), and Imperial College London (supported by the UK Science and Technology Facilities Council).
  • Context. Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce. Aims. Our aim is to demonstrate the existence of cold electrons in the inner coma of comet 67P/Churyumov-Gerasimenko and show filamentation of this plasma. Methods. In situ measurements of plasma density, electron temperature and spacecraft potential were carried out by the Rosetta Langmuir probe instrument, LAP. We also performed analytical modelling of the expanding two-temperature electron gas. Results. LAP data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5-10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order -10 V. Conclusions. The warm (5-10 eV) electron population observed throughout the mission is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming filaments that we observe as pulses.

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  • Engelhardt, Ilka. A. D.Uppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen,Institutionen för fysik och astronomi(Swepub:uu)ilken598 (author)
  • André, MatsUppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen(Swepub:uu)maand125 (author)
  • Boström, RolfUppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen(Swepub:uu)rolfbost (author)
  • Edberg, Niklas J. T.Uppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen(Swepub:uu)niked861 (author)
  • Johansson, Fredrik L.Uppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen,Institutionen för fysik och astronomi(Swepub:uu)frejo741 (author)
  • Odelstad, EliasUppsala universitet,KTH,Rymd- och plasmafysik,Institutionen för fysik och astronomi,Institutet för rymdfysik, Uppsalaavdelningen(Swepub:uu)eliod143 (author)
  • Vigren, ErikUppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen(Swepub:uu)erivi300 (author)
  • Wahlund, Jan-ErikUppsala universitet,Institutet för rymdfysik, Uppsalaavdelningen(Swepub:uu)janewahl (author)
  • Henri, P.LPC2E, Lab Phys & Chim Environm & Espace (author)
  • Lebreton, J. -PLPC2E, Lab Phys & Chim Environm & Espace (author)
  • Miloch, W. J.Univ Oslo, Dept Phys (author)
  • Paulsson, J. J. P.Univ Oslo, Dept Phys (author)
  • Wedlund, C. SimonUniv Oslo, Dept Phys (author)
  • Yang, L.Univ Oslo, Dept Phys (author)
  • Karlsson, Tomas,1964-KTH,Alfvénlaboratoriet,Rymd- och plasmafysik,Royal Inst Technol, Alfvén Lab(Swepub:kth)u154ti5p (author)
  • Jarvinen, R.Finnish Meteorol Inst, Helsinki 00560 (author)
  • Broiles, T.Southwest Res Inst, San Antonio (author)
  • Mandt, K.Southwest Res Inst, San Antonio; Univ Texas San Antonio, Dept Phys & Astron (author)
  • Carr, C. M.Imperial Coll London, Dept Phys (author)
  • Galand, M.Imperial Coll London, Dept Phys (author)
  • Nilsson, H.Swedish Inst Space Phys, S-98128 Kiruna (author)
  • Norberg, C.Swedish Inst Space Phys, S-98128 Kiruna (author)
  • Uppsala universitetInstitutet för rymdfysik, Uppsalaavdelningen (creator_code:org_t)

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  • In:Astronomy and Astrophysics: EDP SCIENCES S A6050004-63611432-0746

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