Characterizing cometary electrons with kappa distributions
File(s)
Author(s)
Type
Journal Article
Abstract
The Rosetta spacecraft has escorted comet 67P/Churyumov-Gerasimenko since 6 August 2014
and has offered an unprecedented opportunity to study plasma physics in the coma. We have used
this opportunity to make the
fi
rst characterization of cometary electrons with kappa distributions. Two
three-dimensional kappa functions were
fi
t to the observations, which we interpret as two populations of
dense and warm (density=10cm
3
, temperature=2×10
5
K, invariant kappa index=10
>
1000), and
rare
fi
ed and hot (density=0.005cm
3
, temperature=5×10
5
K, invariant kappa index=1
–
10) electrons. We
fi
t the observations on 30 October 2014 when Rosetta was 20km from 67P, and 3AU from the Sun. We
repeated the analysis on 15 August 2015 when Rosetta was 300km from the comet and 1.3AU from the Sun.
Comparing the measurements on both days gives the
fi
rst comparison of the cometary electron environment
between a nearly inactive comet far from the Sun and an active comet near perihelion. We
fi
nd that the warm
population density increased by a factor of 3, while the temperature cooled by a factor of 2, and the invariant
kappa index was unaffected. We
fi
nd that the hot population density increased by a factor of 10, while
the temperature and invariant kappa index were unchanged. We conclude that the hot population is
likely the solar wind halo electrons in the coma. The warm population is likely of cometary origin, but its
mechanism for production is not known.
and has offered an unprecedented opportunity to study plasma physics in the coma. We have used
this opportunity to make the
fi
rst characterization of cometary electrons with kappa distributions. Two
three-dimensional kappa functions were
fi
t to the observations, which we interpret as two populations of
dense and warm (density=10cm
3
, temperature=2×10
5
K, invariant kappa index=10
>
1000), and
rare
fi
ed and hot (density=0.005cm
3
, temperature=5×10
5
K, invariant kappa index=1
–
10) electrons. We
fi
t the observations on 30 October 2014 when Rosetta was 20km from 67P, and 3AU from the Sun. We
repeated the analysis on 15 August 2015 when Rosetta was 300km from the comet and 1.3AU from the Sun.
Comparing the measurements on both days gives the
fi
rst comparison of the cometary electron environment
between a nearly inactive comet far from the Sun and an active comet near perihelion. We
fi
nd that the warm
population density increased by a factor of 3, while the temperature cooled by a factor of 2, and the invariant
kappa index was unaffected. We
fi
nd that the hot population density increased by a factor of 10, while
the temperature and invariant kappa index were unchanged. We conclude that the hot population is
likely the solar wind halo electrons in the coma. The warm population is likely of cometary origin, but its
mechanism for production is not known.
Date Issued
2016-08-12
Date Acceptance
2016-07-21
Citation
Journal of Geophysical Research. Solid Earth, 2016, 121 (8), pp.7407-7422
ISSN
2169-9356
Publisher
American Geophysical Union (AGU)
Start Page
7407
End Page
7422
Journal / Book Title
Journal of Geophysical Research. Solid Earth
Volume
121
Issue
8
Copyright Statement
© 2016. American Geophysical Union.
All Rights Reserved.
All Rights Reserved.
Sponsor
Science and Technology Facilities Council (STFC)
The Leverhulme Trust
Identifier
http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000385811500006&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=1ba7043ffcc86c417c072aa74d649202
Grant Number
ST/K001051/1
RF-2015-188
Subjects
Science & Technology
Physical Sciences
Astronomy & Astrophysics
GIACOBINI-ZINNER
SOLAR-WIND
SPACE PLASMAS
BOW SHOCK
ROSETTA
67P/CHURYUMOV-GERASIMENKO
COMA
ION
HALLEY
SENSOR
Publication Status
Published