The Termination of the Supersonic Solar Wind

Joe Giacalone

Recently the two Voyager spacecraft crossed the first 
major heliospheric boundary, the solar wind termination 
shock.  Voyager 2, which has an operational plasma 
instrument, observed the fine-scale details associated
with the transition across the shock.  One interesting 
observation is that the solar wind remains supersonic 
in the post-shock region, known as the heliosheath.  
This is, of course, not possible since a shock wave 
is a transition from supersonic to subsonic flow.  The 
answer to this puzzle comes from recognizing the fact 
that the Voyager plasma instrument is incapable of 
measuring an important constituent of the plasma in 
the outer heliosphere, ionized interstellar atoms.  
This physics of the structure of the termination shock, 
and how it accelerates charged particles that ultimately 
become cosmic rays will be discussed in this talk.