To boldly go where no man has gone before
"We’ve entered a totally new region of space."
These words could have been uttered by captain James T. Kirk in the TV series Star Trek, but unlike Kirk, then man who actually said this is not a fictional character, but a real scientist of flesh and blood. His name is Ed Stone and he is a scientist on the Voyager project (and also former director of the Jet Propulsion Laboratory), and he is talking about the space probe Voyager 1, which is our scout in deep space. No space probe has reached as far out in space as Voyager 1. It left earth on September 5, 1977, at which time I was in diapers. Almost thirty years later, it has now reached what may be called the final frontier: the heliosheath.
The heliosheath is where the solar wind slows down and becomes turbulent, effectively forming a shell which envelopes the entrire solar system by a large margin. This is a region of space with potentially lots of interesting physics which has never been accessible to measurements before. The main goal of the Voyager missions was to visit the four gas giants in our planetary system (Jupiter, Saturn, Uranus and Neptune), but the most important result of the missions will be to fulfil the old Star Trek headline: "To boldly go where no man has gone before", to take mankind outside the solar system, not by manned missions, but also not only in spirit. Voyager 1 is now providing us with actual in situ measurements from places that have so far only belonged to the realm of telescopes. The heritage of the Voyager missions, I think, will be what stories Voyager will tell us about the outskirts of the solar system, about regions of space truely foreign to us. I believe our grandchildren will remember Voyager for being our first reach outside the solar system.
And it has proved to be an interesting place indeed:
- The magnetic field is like a dirt road after winter, with sudden jumps in magnetic field strength. Sometimes the field strength drops to almost nothing, from the normal 0.1 nT (nano-Tesla) to 0.01 nT or less, sometimes jumping to twice its normal value.
- The solare wind does not slow down as expected, is slows down much more than it should. The measured solar-wind speed is only about one tenth of the theoretically predicted value.
- While the heliosheath protects the solar system from energetic galactic cosmic rays, it is also the source of cosmic rays. This radiation is called anomalous cosmic rays and is the result of a shockwave at the inner boundary of the heliosheath, which accelerates sub-atomic particels towars the solar system. Or so researchers thought. But Voyager 1 passed the inner boundary of the heliotsheath in 2004 without any change in cosmic ray counts. Now, however, almost two years later, the intensity is increasing.
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