Posted on 11/27/2007 8:04:05 PM PST by Excuse_My_Bellicosity
RIVERSIDE, Calif. - Using a computer model simulation, Haruichi Washimi, a physicist at UC Riverside, has predicted when the interplanetary spacecraft Voyager 2 will cross the "termination shock," the spherical shell around the solar system that marks where the solar wind slows down to subsonic speed.
According to Washimi's simulations, the spacecraft is set to cross the termination shock in late 2007-early 2008. To make this forecast, Washimi and his colleagues used data from Voyager 2 and performed a global "magneto-hydrodynamic simulation" - a method that allows for precise and quantitative predictions of geomagnetic disturbances caused by solar activities.
Because Voyager 2's crossing of the shock is expected to be an abrupt and relatively brief event, scientists are working to ensure that the most is made of the opportunity. With an idea of when the spacecraft will cross the shock, they are better able to maximize coverage of the crossing.
Study results appear in the Dec. 1 issue of The Astrophysical Journal.
"Washimi's model has predicted the location of a boundary that is approximately 90 times farther from the sun than is the Earth, to within a few percent," said Gary Zank, the director of the Institute of Geophysics and Planetary Physics and one of the coauthors of the research paper. "This is truly remarkable given the enormous complexity of the physics involved, the temporal and spatial scales involved, and the variability of the solar wind conditions."
The solar wind - a stream of charged particles ejected by the sun in all directions - travels at supersonic speeds when it leaves the sun, until it eventually encounters the interstellar medium made up of plasma, neutral gas and dust.
At the termination shock, located at 7-8.5 billion miles from the sun, the solar wind is decelerated to less than the speed of sound. The boundary of the termination shock is not fixed, however, but wobbly, fluctuating in both time and distance from the sun, depending on solar activity.
"This is the first time the termination-shock position has been forecast in this way," said Washimi, the lead author of the research paper and a scientist at the Institute of Geophysics and Planetary Physics. "After it crosses this boundary, Voyager 2 will be in the outer heliosphere beyond which lies the interstellar medium and galactic space. Our simulations also show that the spacecraft will cross the termination shock again in the middle of 2008. This will happen because of the back and forth movement of the termination-shock boundary. This means Voyager 2 will experience multiple crossings of the termination shock. These crossings will come to an end after the spacecraft escapes into galactic space."
Voyager 2 was launched Aug. 20, 1977. It visited four planets and their moons in the course of its journey into space. Its sister spacecraft Voyager 1, which was launched Sept. 5, 1977, crossed the termination shock in December 2004 - earlier than Voyager 2 because of a shorter trajectory. Both spacecraft are currently operational, but power sources have degraded and some of the instrumentation no longer works optimally. In the future, the spacecraft will encounter their next milestone in space: the heliopause, which is the boundary where the interstellar medium brings the solar wind to a halt.
I find it downright amazing that they still work.
Must be Energizer Batteries :>)
Voyager 2 was launched before Voyager 1?
Did you ever see the movie Starman? I love the scene where the Voyager is playing “Satisfaction” as it enters the atmosphere of the alien planet.
Ditto. I’m also amazed that they haven’t sent an ion propulsion probe on a track out of the solar system yet. It would be able to pass both voyagers out in 10 years or so.
Wow, 30 years to get to the outreaches of our solar system — which is just a tiny point in the Milky Way galaxy, which is such a tiny part of the entire known universe......
Ping
And just exactly what is the speed of sound, up there, in space?
so, how does one decelerate from zero to say, zero?
This link has the spacecrafts distance and location:
http://www.heavens-above.com/solar-escape.asp?/lat=0&ing=0&loc=Unspecified&alt=o&tz=CET
Much better link than mine. Thanks. Should have remembered Heavens Above, a very good site and I use it frequently.
So, instead of sails, they’ll have to use outboard engines?
That was my thought too - what does the speed of sound (compression waves in a gas) have to do with charged particles in a vacuum? Is it just a velocity? Or does it just happen that the sudden deceleration of the charged particles happens to fall across the nominal speed of sound?
Shhh, this hypothesized phenomena has go to be good for a few hundred thousand in grant money for Mr. Washimi.
proly mean the speed of light, cause sound speed is not too terribly fast up there in all that space. It would take a few billion years for the charges particles to get to the spot in question going at 1100 ft/sec, provided there was enought molecules close enough to each other to do a 1100ft /sec wave.
Roughly 100km/sec in the interstellar mediun.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.