Postcards from the Edge
There are no signs to announce the edge of the solar system, but when the venerable Voyager 2 spacecraft approached this final frontier last Aug. 31 it was in for quite a shock. So were the scientists who analyzed the data that the craft radioed back to Earth, along with related observations by NASA’s twin Earth-orbiting STEREO spacecraft.
The signals reveal that at a distance of 83.7 astronomical units (1 AU is the average Earth-sun separation), Voyager 2 had at least five encounters with a turbulent region known as the termination shock. That’s the place where the solar wind — the sun’s hot supersonic wind of protons and other charged particles, which carves the heliosphere, a bubble in space extending well beyond the orbit of Pluto — slams into cold interstellar space and abruptly slows…
Researchers had expected that Voyager 2 would have only one encounter with the shock. The multiple crossings indicate that “the shock is not the steady structure that is predicted by the simplest theory,” says Len Burlaga of NASA’s Goddard Space Flight Center. “It is like a wave approaching a beach, that grows, breaks, dissipates, and then re-forms closer to shore…”
“Over the past few years, the stream of in situ and remote data from the outer reaches of the heliosphere has revolutionized our view of how the sun interacts with the galaxy,” comments J.R. Jokipii. More is to come, he adds, as the two Voyager craft continue their journeys past the termination shock, to the very edge of the solar system during the coming decade.
It’s a positive comment on the class of construction in these early Voyagers that they’re still chugging along, sending messages back home.
Cripes, we have cellphones with more computing power than these critters, nowadays. But, they’re still providing valuable information about the world around us. And beyond.