OUR SOLAR SYSTEM sits like a bubble in space, its edges delineated by the solar wind - the energetic particles from the sun that flow out in all directions. But ours is a lop-sided bubble and one that has a serious dent - caused by an as yet unknown magnetic source.
Much of what we know about the edges of our solar bubble come from two satellites that are well-placed to tell us about the cross-over point, the so-called "termination shock" where the solar system ends and outer space begins. Voyager 1and Voyager 2have both crossed through the termination shock and are now the two most distant objects ever launched into space.
Today's edition of the journal Naturecelebrates the Voyagerpair. It includes no less than five research papers interpreting data from the satellites and a "news and views" report that explains the importance of the Voyagersand describes what they have told us about conditions outside of our solar system. The single most remarkable thing about the Voyagersis they have been beaming back data on a daily basis for more than 30 years. Launched in 1977, they initially did fly-bys of the outer giant planets Jupiter, Saturn, Uranus and Neptune. They sent back thousands of images and also toured 48 of the moons circling these planets.
All of this was achieved using what we would view as the "antique computers" available in 1977, when calculators were advanced technology and when an inferior version of today's cheapest laptops would have required enough hardware to fill up a typical sitting room. While the processing might be somewhat limited the Voyagersstill work, a testament to the durability of that old technology.
Voyager 1survived its transit of the termination shock four years ago and is now 15,795 million kilometres (m km) away. Its sister satellite has also crashed through and is now 12,750m km away. But while the first crossed at 14,100m km, the second hit the termination shock at only 12,600m km distant.
The sun's solar wind flows outward at up to 900,000km per hour, but slows dramatically to about 250,000km per hour at the termination shock. This crossover point varies however, as shown by the Voyagers in situ and also by newer satellites such as the Stereospacecraft and the soon to be launched Ibexsatellite, which will be able to "see" this point of intersection from earth orbit.
The Voyager 2crossing also confirmed information from Voyager 1that there is a dent in our bubble. It is pushed in on one side, with scientists speculating that a mystery magnetic field affects the bubble, but can't be seen.
The Voyagersare not finished yet. There is a transitional area where the solar wind dissipates into true outer space or the "interstellar plasma". Its inner edge is known as the "heliosheath", and it ends at the "heliopause".
Scientists remain unsure where the heliopause is, but believe Voyager 1is bound to reach it during the next decade or so. Assuming its nuclear batteries continue to work, it will have much to say when it arrives.
DICK AHLSTROM