Going and going and going... forever

Voyager 2 just crossed the edges of the Solar System on its way to interstellar space. Its twin ship, Voyager 1, did that a while back:

The Voyager 2 spacecraft has crossed an important space frontier called the termination shock, and in a few years may become the first object made by humans to travel outside the solar system.

NASA's two Voyager spacecraft were launched in 1977 to tour the outer solar system. They are now far beyond the orbits of the outermost planets and heading towards interstellar space.

In 2004, the faster of the two spacecraft, Voyager 1, became the first human-made object to reach a boundary called the termination shock. There, the solar wind – made of charged particles from the Sun – suddenly falters as it feels pressure from gas in the interstellar medium lying outside the solar system.

But scientists missed observing the crucial moment because the sensitive radio dishes on Earth needed to hear the spacecraft's transmissions did not happen to be listening at the time.

That's because the dishes are in high demand for other missions, such as Cassini, and therefore cannot listen to the Voyagers around the clock. The Voyagers cannot store their observations onboard, so they are lost forever if they are not relayed to Earth as they are made.

Now, Voyager 2 has crossed the same boundary, and this time scientists were lucky enough to be listening when it happened.
[...]
Voyager 1 and 2 are now both in a region of slower solar wind lying past the termination shock called the heliosheath. That region ends at the heliopause, which is where the solar wind ends and interstellar space begins.

One or the other of the spacecraft will become the first probe to reach interstellar space after a travel period Stone estimates to be about 7 to 10 years long. It is not clear which spacecraft will be first, even though Voyager 1 is about 20 AU farther from the Sun than its sister spacecraft.

Now, scientists know that the termination shock is 84 AU from the Sun in the direction Voyager 2 has traveled – 10 AU closer than in Voyager 1's direction. This confirms earlier measurements that suggested the solar system's boundaries are squashed in one direction because of the influence of the interstellar magnetic field. Depending on how squashed the heliopause is, Voyager 2 could leave the solar system first.

Fascinating. Too bad scientists missed Voyager 1's passage, but at least they didn't lose Voyager 2's transmission. It's such a pity that all that data got lost forever.