"THE HELIOSPHERE - LOVE IT OR LEAVE IT"
Twenty five years ago two Voyager spacecraft were launched
to explore Jupiter, Saturn, Uranus, Neptune, and beyond. They revealed
surprising worlds with distinctive atmospheres, moons, rings, and magnetospheres.
They continue their journeys as the first interstellar probes, searching
for the outer boundary of the heliospheric bubble surrounding the Sun.
The next milestone in the journey is the termination shock where the supersonic
solar wind abruptly slows as it approaches the boundary. The size
of the heliosphere varies over the 11-year solar cycle, and estimates suggest
that the shock is now at its minimum distance of 90 to 100 AU. Voyager
1 at 86 AU is in a race to reach the termination shock before the heliosphere
begins expanding again with the onset of increased solar wind pressure
expected in the next several years.