Interesting Voyager 1 Article

[drwayne]

From here:<br />http://www.physorg.com/news6741.html<br /><br />"We have confirmed, for the first time, that Voyager 1 crossed the termination shock on Dec. 16, 2004," said Frank McDonald , a senior research scientist at the university's Institute for Physical Science and Technology, and a coauthor on two of four Voyager 1 papers published in the Sept. 23 issue of Science. The termination shock marks the beginning of a transition region at the edge of the solar system that is known as the heliosheath. <br /><br />"Until now there has been debate among scientists on whether Voyager 1 had crossed the termination shock as early as 2002 or not until December 16, 2004," said McDonald, who coauthored "Crossing the Termination Shock into the Heliosheath: Magnetic Fields," and "Voyager 1 Explores the Termination Shock Region and the Heliosheath Beyond." Matthew Hill, George Gloeckler and Douglas C. Hamilton, scientists in the University of Maryland's Space Physics Group were among the coauthors of a third article, "Voyager 1 in the Foreshock, Termination Shock and Heliosheath," which presents other new observations on the spacecraft's entrance into the heliosheath. Gloeckler and his Space Physics group built the Low Energy Charged Particle (LCEP) instrument, one of the five main instruments on Voyager. <br /><br />"The termination shock -- a shock wave in the solar wind, that marks the slowing of the supersonic solar wind to subsonic speed -- had been universally thought to be a prodigious accelerator of particles and our findings largely confirm that," said Hill, a research scientist in the department of physics. "This paper describes a remarkable increase in particle intensity with energetic characteristics unlike anything we have seen before. In addition, the LECP instrument indirectly determines that the solar wind speed in the heliosheath is clearly sub-sonic." <br /><br />However, Hill explained that one very sur <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vogon13]

Magellan, Sir Francis Drake, Lewis & Clark, Voyager 1...... <br /><br /><br />SALUTE!<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[CalliArcale]

Cool article! Next time I see my brother, I should ask him about this; he's into cosmic rays. If nothing else, he might be able to explain it to me in a way that I can understand. <img src="/images/icons/wink.gif" /> He's very good at that. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[spacefire]

<font color="yellow">"The termination shock -- a shock wave in the solar wind, that marks the slowing of the supersonic solar wind to subsonic speed -- had been universally thought to be a prodigious accelerator of particles and our findings largely confirm that," said Hill, a research scientist in the department of physics. "This paper describes a remarkable increase in particle intensity with energetic characteristics unlike anything we have seen before. In addition, the LECP instrument indirectly determines that the solar wind speed in the heliosheath is clearly sub-sonic." <br /></font><br /><br />this is a metaphor, right? because sound doesn't propagate in vacuum, and there is no such thing as the speed of sound of Vacuum-sqrt (gamma*R*T)-mainly because gamma doesn't exist for vacuum.<br /> <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[vogon13]

Mechanical disturbances amongst the rarefied particles does not seem to me to contravene any laws of physics.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[tap_sa]

And 'sound' (=pressure waves) <i>does</i> propagate through instellar space which isn't a pure vacuum. While back there was an article about pretty telescope picture of such waves from some pulsing phenomenon. You'd need a pretty high-end subwoofer to hear this sound though, the wavelength was measured in light years.

 

[vogon13]

The majority of time, an individual molecule of N2 in the room with me right now is experiencing a vacuum.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[spacefire]

what would the speed of sound be in such a rarefied environment? <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[vogon13]

Ambiguous.<br /><br />SOS declines as density decreases, but I'm not sure how it works in deep (really) deep space.<br /><br />(Magic 8 ball didn't work this time)<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[CalliArcale]

That's a really good question. I did some digging and found a webpage with some really good information about Voyager 1's crossing of the termination shock. It doesn't give a value for the local speed of sound out there, but it does have an interesting explanation of exactly what the termination shock is and why it's important. The Heliosphere<br /><br />I found another page which gave the speed of sound in the vicinity of Earth as 30-50 kilometers per hour. (The solar wind travels at 400-750 km/hr, so it's definitely supersonic in that environment.)<br /><br />On another page, Galactic Environment of the Sun, I found a good number for us. It gives 9.6 km/sec for the speed of sound in the local interstellar cloud, through which our solar system is travelling. That page estimates that the heliosphere should have a Mach 2.5 bow shock. That's an interesting page too. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[spacefire]

well, the problem seems to be twofold. First of all, we know that the speed of sound decreases with decreasing temperature-from its formula.<br />But what are the gamma and R of near vacuum?<br />what kind of a shockwave can occur in such environment? This termination shock seems to be sort of a normal shock-a pretty violent type of transition in air, which reduces the speed of the flow from supersonic to subsonic. <br />I just can't imagine that type of phenomenon going on in interstellar space <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[CalliArcale]

It's probably the sort of thing where for most purposes that we're used to here on Earth, it's negligible. I mean heck, it's not as if it's having a whole lot of effect on Voyager 1. But it does become significant on a very large scale (both in terms of space and time) with high precision, and in certain applications. For instance, if we're ever to exploit solar sails, this becomes important. Otherwise, I think it's mainly of academic importance right now. Then again, one of the links I read as I looked for the number said something about it affecting cosmic radiation, because particles are more likely to be ionized as they pass through this region, which affects whether or not they are influenced by magnetism. Since the solar wind is electrically charged, that can influence where these particles wind up. But still, pretty academic. <img src="/images/icons/wink.gif" /> A lot of astrophysics is all pure science. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[lampblack]

For some reason, this thread set me to trying to recall from deep memory the specifics of the old sci-fi reference, "In space, nobody can hear you scream."<br /><br />It actually set me to googling. But before I could uncover the reference, I stumbled across this interesting old space.com article on the scientific value of detecting sound waves in space:<br /><br />http://www.space.com/scienceastronomy/mystery_monday_030922.html <div class="Discussion_UserSignature"> <font color="#0000ff"><strong>Just tell the truth and let the chips fall...</strong></font> </div>

 

[CalliArcale]

Ah yes. That's the advertising tag-line from "Alien". <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[spacefire]

'Alien' and 'Aliens' are the best Sci-fi movies IMO <img src="/images/icons/smile.gif" /><br />but I digress....<br />The sound waves propagate faster in air because the particles are close together and the osciallation is transmitted from one to another.<br />In space, with the particles being so far apart, chances are the sound wave will hit you around the same time the original particle hits you, over short distances that is <img src="/images/icons/smile.gif" /> Over long distances you'd get something like a real wave.<br />hope this makes sense, I know we have some really smart people here. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[CalliArcale]

Yeah, that does make sense! Thanks! <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>