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Cometary ion dynamics observed in the close vicinity of comet 67P/Churyumov-Gerasimenko during the intermediate activity period
Swedish Institute of Space Physics, Kiruna.
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Swedish Institute of Space Physics, Kiruna.
Swedish Institute of Space Physics, Kiruna.
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 613, p. 1-8Article in journal (Refereed) Published
Abstract [en]

Aims.Cometary ions are constantly produced in the coma, and once produced they are accelerated and eventually escape the coma.We describe and interpret the dynamics of the cometary ion flow, of an intermediate active comet, very close to the nucleus and in theterminator plane.Methods.We analysed in situ ion and magnetic field measurements, and characterise the velocity distribution functions (mostly usingplasma moments). We propose a statistical approach over a period of one month.Results.On average, two populations were observed, separated in phase space. The motion of the first is governed by its interactionwith the solar wind farther upstream, while the second one is accelerated in the inner coma and displays characteristics compatiblewith an ambipolar electric field. Both populations display a consistent anti-sunward velocity component.Conclusions.Cometary ions born in different regions of the coma are seen close to the nucleus of comet 67P/Churyumov–Gerasimenko with distinct motions governed in one case by the solar wind electric field and in the other case by the position relative tothe nucleus. A consistent anti-sunward component is observed for all cometary ions. An asymmetry is found in the average cometaryion density in a solar wind electric field reference frame, with higher density in the negative (south) electric field hemisphere. Thereis no corresponding signature in the average magnetic field strengt

Place, publisher, year, edition, pages
EDP Sciences, 2018. Vol. 613, p. 1-8
National Category
Fusion, Plasma and Space Physics Aerospace Engineering
Research subject
Atmospheric science
Identifiers
URN: urn:nbn:se:ltu:diva-68784DOI: 10.1051/0004-6361/201732082ISI: 000433880200003OAI: oai:DiVA.org:ltu-68784DiVA, id: diva2:1206754
Note

Validerad;2018;Nivå 2;2018-06-14 (andbra)

Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-06-21Bibliographically approved
In thesis
1. Solar Wind Dynamics within The Atmosphere of comet 67P/Churyumov-Gerasimenko
Open this publication in new window or tab >>Solar Wind Dynamics within The Atmosphere of comet 67P/Churyumov-Gerasimenko
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, we explore the dynamics of the solar wind as it perme-ates and flows through a tenuous cometary atmosphere, with a focuson the interaction observed at comet 67P/Churyumov–Gerasimenko.

Seven comets had already been visited by nine different probes when the European spacecraft Rosetta reached comet Churyumov–Gerasimenko in August 2014. The mission was however the first to orbit its host comet, which it did for a total duration of more than two years, corre-sponding to a large part of the comet’s orbit around the Sun. This en-abled to study how the dynamics of the plasma environment evolvedas the comet itself was transformed from one of the smallest obstaclesto the solar wind in the Solar System when far away from the Sun, toa well-established magnetosphere at perihelion.

Most of our efforts tackle the early part of this transformation, when the creation of new-born cometary ions starts to induce significant disturbances to the incident flow. During this stage, a kinetic descrip-tion of the interaction is necessary, as the system of interest cannot be reduced to a hydrodynamic problem. This contrasts with the situation closer to the Sun, where a fluid treatment can be used, at Churyumov–Gerasimenko as well as at previously visited comets.

Rosetta was not a mission dedicated to plasma studies, however. It directly translates into a limited spatial coverage of the cometary plasma environment, which by its nature extends over several spatial scales. An approach solely based on the analysis of in-situ data cannot properly address the major questions on the nature and physics of the plasma environment of Churyumov–Gerasimenko. This thesis there-fore largely exploits the experimental–analytical–numerical triad of approaches. In Chapters 3 and 4 we propose simple models of the ion dynamics and of the cometary plasma environment, and these are tested against experimental and numerical data. Used together,they give a global description of the solar wind ion dynamics through the cometary atmosphere, that we explore in the 2-dimensional and 3-dimensional cases (Chapter 5). In Chapter 6, we propose a view onthe interaction and its fluid aspects when closer to the Sun.

Abstract [sv]

I  denna  avhandling  undersöks  solvindens  dynamik  när  den  flödar genom  en  tunn  kometatmosfär,  med  fokus  på  den  interaktion  somobserverats vid kometen 67P/Churyumov-Gerasimenko.

När  Rosetta  nådde  from  till  komet  67P/Churyumov–Gerasimenko  i augusti 2014 hade redan sju olika rymdfarkoster besökt nio olika ko- meter.  Rosetta  var  dock  den  första  missionen  som  cirklade  runt  en komet och följde den sedan i dess bana i totalt mer än två år. Detta motsvarade en signifikant del av hela kometens bana runt solen. Det- ta gjorde det möjligt att studera plasmats dynamiska utveckling un- der en period när kometen utvecklades från ett av de minsta hindren solvinden möter i solsystemet, när kometen är långt från solen, till enfullt utvecklad magnetosfär nära perihelion.

Avhandlingen behandlar främst den tidiga delen av denna utveckling, när nyligen joniserade molekyler från kometatmosfären börjar ge en signifikant störning i solvindens flöde. Under dessa förhållanden är en kinetisk beskrivning av växelverkan mellan solvinden och kome- tatmosfären  nödvändig.  Systemet  vi  studerar  kan  inte  reduceras  till ett hydrodynamiskt problem. Detta till skillnad från situationen när kometen är närmare solen, då växelverkan kan beskrivas med fluid- teori, för både Churyumov–Gerasimenko och de tidigare undersöktakometerna.

Rosetta var inte en mission främst ägnad åt plasma-studier. Detta med- förde begränsad rumslig täckning av de plasma-processer som äger rum, vilka äger rum över flera olika rumsskalor. Att förstå solvindens växleverkan  med  kometatmosfären  enbart  med  enpunktsmätningar låter sig därför inte göras. I detta arbete används därför en kombina- tion av experimentella data, analytiska beskrivningar och numeriska beräkningar. I kapitel 3 och 4 föreslår vi enkla modeller för att beskri- va jondynamiken och kometens plasmamiljö. Dessa testas sedan mot observationer och numeriska modeller. Tillsammans ger de en global beskrivning  av  solvindens  dynamik  när  den  flödar  genom  kometat- mosfären,  vilket  utforskas  i  både  2 och  3 dimensioner  (kapitel  5).  I kapitel 6 utforskar vi interaktionen som sker när kometen är närmaresolen, och hur den nu i högre grad kan beskrivas som en fluid.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Fusion, Plasma and Space Physics Aerospace Engineering
Research subject
Space Technology
Identifiers
urn:nbn:se:ltu:diva-68785 (URN)978-91-7790-156-3 (ISBN)978-91-7790-157-0 (ISBN)
Public defence
2018-10-12, Aulan, IRF, Rymdcampus, Kiruna, 09:00 (English)
Opponent
Supervisors
Available from: 2018-05-21 Created: 2018-05-18 Last updated: 2018-10-10Bibliographically approved

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