Estimates of the Size of the Ionosphere of Comet 67P/Churyumov–Gerasimenko During Its Perihelion Passage in 2014/2015 - Planetary Exploration and Science: Recent Results and Advances - page 269

Fig. 10.3 Comparisons of the size of the diamagnetic cavity ( R max ) and the location of the electron
temperature discontinuity ( R e ), respectively, at different heliocentric distances of comet 67P

10.3 Ion Pile-Up Region

The exact profile of the magnetic field ahead of the diamagnetic cavity is determined
by a number of factors. The spatial and temporal variations of the draped interplan-
etary magnetic field (IMF) could lead to the formation of thin current sheets and
probably flux ropes also. A case in point is the so-called ion tail disconnection
events. It was suggested that encounter of a cometary ionosphere with the sector
boundary of the IMF where the magnetic polarity reverses by 180 ı could lead to
magnetic reconnection and hence the detachment of the “old” ion tail from the
cometary coma (Niedner and Brandt 1978 ;Yietal. 1994 ).
Other mechanisms such as plasma instabilities generated by interaction with
solar wind events (i.e., CMEs) have also been investigated (Ip and Mendis 1978 ;
Wa n g 1991 ;Wegmann 2000 ;Voelzke 2005 ). Small-scale structures like the for-
mation of ion rays could also be related to solar wind disturbances (Bonev and
Jockers 1994 ). Based on the detection of an ion pile-up region at comet Halley by the
plasma instruments of the Giotto spacecraft (Balsiger et al. 1986 ) and its subsequent
interpretation as the signature of a sharp electron temperature discontinuity (from
T e 100 K to about 10 4 K) in the cometary ionosphere (Ip et al. 1987 ; Gan and
Cravens 1990 ), it has been proposed (Ip 1994 ) that expansion or contraction of the
boundary of the electron temperature discontinuity could also lead to the ion source