Voyager Spacecraft Will Reach Major Milestone in Late 2007 or Early 2008

[freeztar]

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.

lefthttp://hypography.com/gallery/files/2/5/2/6/1720_0hi_thumb.jpg[/img]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.

 

Washimi and Zank were joined in the research by UCR's Qiang Hu; Takashi Tanaka of Kyushu University, Japan; and Kazuoki Munakata of Shinshu University, Japan. The research was funded by grants from the National Science Foundation and the National Aeronautics and Space Administration.

 

Source: University of California Riverside

[Buffy]

Sooooooo....

 

...as we all know, the speed of sound is variable and is a function of the temperature of the gas it is traveling through, so Mach 1 at high altitude where its really cold is much lower than it is at sea level (where it would produce a very pretty rooster tail! :rolleyes: )...

 

But its gotta be *really* cold out at that heliopause, like near [math]0^{\circ} K[/math]!

 

So how fast *is* the speed of sound way out there?

 

"Dateline: Pasadena, CA - Little Old Lady Breaks Sound Barrier In Volkswagen," :cheer:

Buffy

[freeztar]

Sooooooo....

 

...as we all know, the speed of sound is variable and is a function of the temperature of the gas it is traveling through, so Mach 1 at high altitude where its really cold is much lower than it is at sea level (where it would produce a very pretty rooster tail! :rolleyes: )...

 

But its gotta be *really* cold out at that heliopause, like near [math]0^{\circ} K[/math]!

 

So how fast *is* the speed of sound way out there?

 

Wouldn't it also depend on the type of gas(es) and how dense it is (they are) as well?

[Buffy]

Wouldn't it also depend on the type of gas(es) and how dense it is (they are) as well?

Nope! Check out the wiki page on the speed of sound...

 

The charms of a passing woman are usually in direct relation to the speed of her passing, :doh: :hihi:

Buffy

[freeztar]

Nope! Check out the wiki page on the speed of sound...

 

In fact, assuming an ideal gas, the speed of sound c depends on temperature only, not on the pressure or density (since these change in lockstep for a given temperature and cancel out).

 

Emphasis mine...:)

 

Btw, the wiki article gives the general equation for the speed of sound, which has density as a variable.

 

Also from the wiki:

All other things being equal, sound will travel more slowly in denser materials, and faster in stiffer ones. For instance, sound will travel faster in iron than uranium, and faster in hydrogen than nitrogen, due to the lower density of the first material of each set.

 

Let's go flying at the speed of sound, show you where it all began ;)

[DougF]

First Measurements Of The Solar Wind Termination Shock By Voyager 2 Spacecraft

 

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ScienceDaily (July 3, 2008) — Two University of Iowa space physicists report that the Voyager 2 spacecraft, which has been traveling outward from the Sun for 31 years, has made the first direct observations of the solar wind termination shock, according to a paper published in the July 3 issue of the journal Nature.

 

 

At the termination shock the solar wind, which continuously expands outward from the sun at over a million miles per hour, is abruptly slowed to a subsonic speed by the interstellar gas. Don Gurnett, professor of physics in the College of Liberal Arts and Sciences and principal investigator for the plasma wave instrument on Voyager 2, and Bill Kurth, UI research scientist and Voyager co-investigator, said that the shock crossing was marked by an intense burst of plasma wave turbulence detected by the UI instrument, as well as by various effects detected by other instruments on the spacecraft.

 

At the time of the shock crossing, August 31, 2007, Voyager 2 was at a distance of 83.7 astronomical units (AU), roughly twice the distance between the Sun and Pluto. At this great distance, it took 11.2 hours for the radio signal from the spacecraft to reach Earth.

 

First Measurements Of The Solar Wind Termination Shock By Voyager 2 Spacecraft