Thirty years after launch but earlier than expected, Voyager 2 has left the cozy realm of our solar system, where the stream of particles from the sun dominates space. You might think that space billions of miles from the sun is a placid, empty domain. In fact, Voyager 2 has been heading outward in the same direction as the solar wind, charged particles streaming from the sun, but things started to get a lot more complicated on August 30, when the spacecraft was 7.8 billion miles from the sun.

There, the spacecraft passed into a new region, where the solar wind suddenly slams into the prevailing breeze and magnetic field left from a series of massive supernovas from 20 million to 30 million years ago, said Voyager project scientist Edward Stone of the California Institute of Technology during a news conference at the American Geophysical Union conference here Monday.

In this area, called the termination shock, the speed of the solar wind drops abruptly from about 250 miles per second to about 60, said John Richardson, a Massachusetts Institute of Technology researcher who’s the principal investigator for the Voyager’s plasma science work.

Voyager 1, which is traveling faster than Voyager 2 and in a different direction, already crossed the termination shock boundary in December 2004, though some of its elderly instruments are defunct and it crossed during a gap when data wasn’t recorded. But Voyager 2 crossed the boundary while significantly closer to the sun, indicating that this region where the solar wind dominates, called the heliosphere, is not in fact a sphere but rather is squashed.

“The termination shock is 1 billion miles closer to the sun in the southern hemisphere than in the northern hemisphere,” Stone said, referring to regions of space on either side of plane in which the planets orbit the sun. “There’s something outside pushing in on the field of the heliosphere. We believe it’s a magnetic field distorting an otherwise spherical surface.”

It’ll be a while–probably 7 to 10 years–before the Voyager spacecraft leave the solar system altogether and cross into interstellar space itself, Stone said. The researchers hope that will be before the Voyagers’ radioactively powered batteries are estimated to run out of juice–sometime between 2020 and 2025, he added. [news.com]