Noun
heliosheath (plural heliosheaths)
(astronomy) A zone between the termination shock and the heliopause, in the heliosphere, at the outer border of the Solar System, where the solar wind is dramatically slower than within the termination shock.
After entering into the heliosheath the spacecraft are in an area that is dominated by the Sun's magnetic field and solar wind particles. Source: Internet
The outer boundary of the heliosheath is called the heliopause which is where the spacecraft are headed now. Source: Internet
The thickness of the heliosheath is not known clearly so the time required to transverse this space is not quite clear. Source: Internet