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The region in the heliosphere between the termination shock and the heliopause.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
References in periodicals archive ?
Now, as Voyager 2 punches the heliosheath to join Voyager 1 in interstellar space, these hoary spacecraft are nearing the end of their scientific lifetimes.
Eventually, it reaches pressure balance with the local interstellar medium at a boundary called the heliopause; the transition region between these boundaries is called the inner heliosheath. The region beyond the heliopause, where the interstellar medium is affected by the presence of the heliosphere, is called the outer heliosheath.
The spacecraft has now cantered off into a new role where it studies the point in space where the influence of our yellow sun ends, and the solar wind and the sun's magnetic field interact with the neighboring interstellar wind - the heliosheath. 
"Instead of a prolonged, comet-like tail, this rough bubble-shape of the heliosphere is due to the strong interstellar magnetic field-much stronger than what was anticipated in the past-combined with the fact that the ratio between particle pressure and magnetic pressure inside the heliosheath is high," said Kostas Dialynas, a space scientist at the Academy of Athens in Greece and lead author on the study.
2012 - Our Voyager 2 probe enters the "heliosheath"— the outermost layer of the heliosphere.
Voyager II is past what we used to think of as the solar system, but it is still in the heliosheath, approaching the (theoretical) edge of the Oort cloud.
These materials interact at the heliosphere's edge to create a region known as the inner heliosheath, bounded on the inside by the termination shock -- which is more than twice as far from us as the orbit of Pluto -- and on the outside by the heliopause, the boundary between the solar wind and the comparatively dense interstellar medium.
It has spent recent years studying the heliosheath, which surrounds the outer edge of the solar system, where the sun's influence wanes.
(138) The heliosheath is a bubble of charged particles where the Sun's solar wind that meets the solar wind from interstellar space that forms a bubble of charged particles at the edge of our solar system.
(2012) No meridional plasma flow in the heliosheath transition region.
Since December 2004 when Voyager 1 crossed a point in space called the termination shock, the spacecraft has been exploring the heliosphere's outer layer, called the heliosheath. In this region, the stream of charged particles from the Sun known as the solar wind abruptly slowed down from supersonic speeds and became turbulent.