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Voyager 2 Set to Reach Termination Shock 308

Posted by CmdrTaco
from the cool-stuff-you've-never-heard-of dept.
Invisible Pink Unicorn writes "A computer model simulation developed at UC Riverside has predicted that in late 2007 to early 2008, 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. 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. Because of this fluctuation, the spacecraft is also predicted to cross the boundary again in middle 2008. The article abstract is available from The Astrophysical Journal."
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Voyager 2 Set to Reach Termination Shock

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  • speed of sound (Score:2, Interesting)

    by AndyST (910890)
    speed of sound... wait a minute? In which medium? I don't think there is much atmosphere up there...
    • by qbwiz (87077) *
      The medium is, in fact, the solar wind.
      • No (Score:5, Informative)

        by InvisblePinkUnicorn (1126837) on Wednesday November 28, 2007 @12:42PM (#21506993)
        No, it is not. It is the interstellar medium. Read: termination shock [wikipedia.org].
        • Bingo (Score:2, Informative)

          by Prefader (1072814)
        • Re:No (Score:5, Informative)

          by E++99 (880734) on Wednesday November 28, 2007 @02:20PM (#21508229) Homepage

          No, it is not. It is the interstellar medium. Read: termination shock.

          No it's not. The Wikipedia article is wrong were it implies that, and right where it says "At the termination shock, a standing shock wave, the solar wind falls below its speed of sound and becomes subsonic." Read Hydrolic Jump [wikipedia.org] and Supercritical flow [wikipedia.org]. The termination shock happens when the solar wind transitions from supercritical to subcritical, which is dependent on its own density, and its own wave speed (speed of sound), not the wave speed of the interstellar medium, which is much further out. While the wave speed of the interstellar medium is given by the article as 100km/s, the density and wave speed of the solar wind can't be expressed as a constant, as it is a function of distance from the sun and heliolatitude.
          • Re: (Score:3, Insightful)

            by jtcm (452335)

            While the wave speed of the interstellar medium is given by the article as 100km/s

            I read that in Wikipedia too, but it doesn't seem right. How is it possible that sounds travels so quickly through such a sparse medium? Here on Earth, the speed of in air is about 340 m/s. In water, where the molecules are closer together and can collide in more rapid succession, the speed is about 1500 m/s. In steel it's about 5000 m/s.

            So how is it that compression waves travel almost 100 times faster through the sparse s

    • Re:speed of sound (Score:4, Interesting)

      by InvisblePinkUnicorn (1126837) on Wednesday November 28, 2007 @12:40PM (#21506951)
      The speed of sound in the interstellar medium is much higher than it is on earth. In case you didn't know, space is not empty. Vacuum is, but space isn't.
      • That's Garbage (Score:3, Insightful)

        by Crazy Taco (1083423)

        The speed of sound in the interstellar medium is much higher than it is on earth. In case you didn't know, space is not empty. Vacuum is, but space isn't.

        That's garbage. Space is not a total vacuum, it's true. However, the density of particles of matter in space is, for the most part, so low that space can be treated as a vacuum. It's like rounding 0.1xE-25 to just 0.

        And as for the whole thing about sound travelling faster in space, you just made that up. Light (and other electromagnetic phenomena) do t

        • 0.1xE-25

          I apologize but the nerd in me has to ask, why not 1.0E-26? Is it some kind of psychological thing that makes the number look significantly smaller, like pricing at (x-1).99 rather than x.00?

          To other readers, yes I know that (x-1).99 != x.00. Notice the word "significantly" and note the context of psychology of pricing.
          • I have heard that some stores use the cents part of the price to indicate a category of pricing. For example, $x.99 is regularly priced, $x.98 is sale priced, $x.97 is clearance priced, etc.
            • by Bob-taro (996889) on Wednesday November 28, 2007 @02:44PM (#21508515)

              I have heard that some stores use the cents part of the price to indicate a category of pricing. For example, $x.99 is regularly priced, $x.98 is sale priced, $x.97 is clearance priced, etc.

              Today only! Closeout prices! Everything in the store is 3 cents off! That's right, 3 cents off! That's lower than sale price! Even lower than clearance sale price! Don't miss this amazing opportunity!

        • Re:That's Garbage (Score:5, Informative)

          by kebes (861706) on Wednesday November 28, 2007 @01:45PM (#21507799) Journal
          You're making a few mistakes...

          Space is not a total vacuum, it's true. However, the density of particles of matter in space is, for the most part, so low that space can be treated as a vacuum. It's like rounding 0.1xE-25 to just 0.
          Rounding and approximations cannot be treated as glibly as you are doing. Approximating outer space as a perfect vacuum is a reasonable approximation for many calculations, but not all. For instance when calculating the properties of light traveling through outer space over short distances (e.g. less than a light year) saying it is a "perfect vacuum" is fine. But when doing calculations over long distances (billions of light years), the thin interstellar medium does indeed induce absorption and polarization effects that must be considered.

          So you cannot always assume that "near vacuum" and "perfect vacuum" are the same thing. In the case of solar wind interacting with the interstellar medium, you can't approximate either as having zero density: to do so would ignore some very real physics that occurs when the pressure of the high-velocity solar wind impinges on the nominally static interstellar medium.

          And as for the whole thing about sound travelling faster in space, you just made that up.
          Every material (even low-density materials like the interstellar medium) have a "speed of sound." The interstellar medium is no different. It has a "speed of sound" on the order of 10 km/s to 100 km/s (by comparison the speed of sound for air on Earth is 0.3 km/s).

          Sound travels faster and farther through more solid materials.
          You're being imprecise by saying that sound travels faster in more "solid" materials. The equation is [wikipedia.org]:
          v = sqrt( C/d )
          where v is the speed of sound, C is the coefficient of stiffness, and d is the density. So, actually, more dense materials have a lower speed of sound (all other things being equal). The reason that liquids and solids have higher speed of sound is not because they are dense, but rather because they have strong cohesive forces binding the constituent atoms/molecules together (that's why they are condensed into a solid or liquid, after all). These strong forces lead to a very high coefficient of stiffness, compared to a gas (more than enough to offset the higher density).

          For something like the interstellar medium, the stiffness is quite low, but the density is exceedingly low, which produces a correspondingly large speed of sound.

          Sound, however, is caused waves of physical compression. In other words, one particle bumps into the next, which bumps into the next, and so on.
          You're quite right. However nothing prevents compression waves from traveling in low-density materials. The atoms of the material are free to fly large distances, and they will indeed statistically bump into each other, transfer momentum, and so on. This collective motion will indeed be compression waves. Of course you will not be able to set up very large-amplitude compression waves using, e.g. your vocal cords in such a low-density medium... but the high-speed collision of the solar wind with the interstellar medium will most certainly lead to all kinds of expanding pressure waves, whose behavior is dependent on the local speed of sound.

          These pressure-wave effects are of course difficult to measure in such a low-density medium, but they are certainly real.
          • by glaswegian (803339) on Wednesday November 28, 2007 @03:00PM (#21508817)

            But when doing calculations over long distances (billions of light years), the thin interstellar medium does indeed induce absorption and polarization effects that must be considered.
            The effects happen on much smaller scales than this, and will depend on the density of matter that the light crosses. You can simply look at an optical image [sas.org.au] towards the centre of our Galaxy. It is only ~25000 light years away and has a huge concentration of stars. It should be a blazing ball of light but it is obscured by a dark "shadow".

            This is the effect of minute "dust" particles permeating space and absorbing/deflecting light. The effect is less for longer wavelengths which is why we can get a better view of the Galactic centre in the infrared [caltech.edu].

        • Re:That's Garbage (Score:5, Interesting)

          by AndersOSU (873247) on Wednesday November 28, 2007 @01:50PM (#21507875)
          It's not garbage. The density of matter in space is important, and speed of sound is applicable.

          Think of it this way, if your sitting in the next cubicle over and I whisper something and you are unable to hear it, does that mean that the speed of sound doesn't exist, or simply that the amplitude of the signal was too small? Similarly, in order to transmit sound in space I'd need some serious lungs. More to the point the speed of sound is a critical parameter when examining how two flows (such as the solar wind and the interstellar medium) interact. Simply put if the speed of sound in the interstellar medium were undefined it would not interact with the solar wind, and there wouldn't be a termination shock at all. Every particle of the solar wind would not interact with any particles of the interstellar medium.

          It's been a while since I've done any fluid dynamics, so some of the details may not be precisely right, and I am not knowledgeable enough on rarefied systems to comment on why the speed of sound is so high in the interstellar medium, but suffice to say that many things behave in counter-intuitive ways for rarefied systems.
  • by tompaulco (629533) on Wednesday November 28, 2007 @12:33PM (#21506829) Homepage Journal
    What exactly is the speed of sound in a vacuum?
    • There's still solar particles out there, however sparse.. normally they move too fast for devices on earth to measure... at this point the device will be going faster than solar particles... kind of cool that the device has "outrun" it's home star.
      • by inviolet (797804)

        There's still solar particles out there, however sparse.. normally they move too fast for devices on earth to measure... at this point the device will be going faster than solar particles... kind of cool that the device has "outrun" it's home star.

        If that is true, then the device will begin slowing down, ever so gradually, as it runs into random interstellar particles, and as it runs over the slower particles of the solar wind.

    • Re:Remind me again (Score:5, Informative)

      by Veinor (871770) <veinor&gmail,com> on Wednesday November 28, 2007 @12:43PM (#21507017)
      Space is not a vacuum. The speed of sound in space is about 100 km/s, according to Wikipedia. [wikipedia.org]
    • Re:Remind me again (Score:5, Informative)

      by kimvette (919543) on Wednesday November 28, 2007 @12:44PM (#21507027) Homepage Journal
      That's what I was wondering. How can there be a speed of sound in a "medium" which does not have enough mass to transmit sound waves? I mean, I know there are sparsely-distributed particles even in "empty" interstellar space, but is the medium thick enough that there can even be a "speed of sound" associated with it? Can sound transmission in such a medium ever even be measured? I was curious and googled on desity of matter in space and found this:

      http://library.thinkquest.org/C0126626/fate/fate%20of%20universe.fate%20of%20universe.mass%20density%20of%20the%20universe.htm [thinkquest.org]

      The most obvious technique for discriminating between an open and a closed universe is to measure the average density of matter. The Friedmann equation describes the competition between the attractive gravitational force and the expansion of the universe. The gravitational attraction exerted at the center of an arbitrary sphere cut out of the universe is proportional to the average density of matter. The measured value of the Hubble constant (H) yields the kinetic energy of the expansion of the sphere. If the present density is below the critical value at which the expansion and gravitational attraction balance, gravity cannot halt the expansion, and the universe must be open. The critical density for closure of the universe is



      d critical = 3H2/8G = 5×10-30 gram cm-3



      [sorry the equation got munched! -Kim]

      where G is Newton's constant of gravitation. Another way to express this critical density is in the number density of atoms, which amounts to 3 x 10-6 atoms per cubic centimeter (cm-3), or only 3 atoms per cubic meter.





      3 atoms per cubic meter is actually higher than I expected it would be given the immense (infinite? It certainly can't be definitively measured by any means we have, only theorised and later disproven) size of the Universe. Is 3 atoms per cubic meter enough to even have a "speed of sound" associated with it?
      • Re:Remind me again (Score:5, Informative)

        by cnettel (836611) on Wednesday November 28, 2007 @12:49PM (#21507105)
        That number of 3 atoms per cubic meter is the average density of the complete universe, inluding stars, planets and black holes, but also including the vast void between galaxies. Any place in the Milky Way, and especially in the relative vicinity of the Sun, is "much" denser.
      • A Few Things (Score:4, Informative)

        by BlackGriffen (521856) on Wednesday November 28, 2007 @01:24PM (#21507557)
        As another reply already noted, this is the interstellar medium, which should be a good deal dense than the space between galaxies and galaxy clusters.

        Next, how does sound transmit? Well, sound is a density/pressure wave, right? All I need is for the free particles to be interacting somehow to set one up. Turns out, the interstellar medium isn't a gas like you're used to thinking of, it's a plasma. The important point here being that because the electrons are not bound to the atoms, the effective "size" of the atoms goes up (that is, the disntance over which they interact with neighboring atoms). Thus you should be able to get sound waves more easily than you would suspect from a regular gas that is that sparse.
      • While it's not as DENSE, since sound is just energy, the atoms carry the energy (and the vacuum between transmits the energy) but there's not enough atoms to really stimulate your eardrum. That is, provided you could take your helmet off in the relative vacuum of space and survive, there's just simply not enough mass present to allow stimulation of our aural system.
      • by jbeaupre (752124)
        I got to wondering myself and did a bit of searching. Turns out that the speed of sound in space is not due to particle collisions as much as it due to magnetic interactions of the ionized atoms. It's the magnetic fields bouncing off one another. If you're curious to learn more, the place I started was http://www-istp.gsfc.nasa.gov/Education/wtermin.html [nasa.gov]. From that clue I came across http://en.wikipedia.org/wiki/Alfv%C3%A9n_wave [wikipedia.org], but I'm not about to do the math to confirm the speed of sound in space.
    • by gclef (96311)
      These guys [sciencedirect.com] seem to think it's 100km/sec.
    • Re: (Score:3, Informative)

      In space, it is much higher than the speed of sound on earth. Tens of kilometers per second, a couple orders of magnitude faster than on earth. See, space is not empty.
    • Re:Remind me again (Score:4, Informative)

      by Sockatume (732728) on Wednesday November 28, 2007 @12:52PM (#21507145)
      Neither the interstellar medium nor the stellar medium is a true vacuum though. The solar wind comes out of the sun faster than the speed of sound in the interstellar medium, in the same way that the expanding sphere of gases from an explosion moves faster than the speed of sound in the air around it. The breakneck expansion of the solar wind and the pressure of the interstellar medium (such as there is) eventually come into equilibrium once you get far enough from the sun. This boundary is your shock front, or in this specific case, the termination shock. What's interesting to me is that changes in the pressure of the solar wind should set up shock waves in the interstellar medium. Please note IANAAstronomer, just an interested postgrad with Google at hand.
    • by davidsyes (765062)
      Hoover Speed
      Bissel Speed
      Oreck Speed
      Haier Speed

      No, wait...

      Gemini Universal Speed....?

      Actually, I wonder what would happen TO a vacuum cleaner powered up and turned on in space. I wonder if it would suck to death. How long before the bag fills up?

      And would a Hepa Bag or unit collect much of value?

      How long would dust mites survive in space (say, not too hot, not too cold, but just in vacuum... they survive cold-water laundering...)
  • cool (Score:3, Interesting)

    by wwmedia (950346) on Wednesday November 28, 2007 @12:33PM (#21506833)
    but can someone describe in layman's term what will that mean for the probe (if anything), will it change course/direction? can this negatively affect the mission/spacecraft itself?
    • by calebt3 (1098475)
      Yes [slashdot.org]
    • Re:cool (Score:5, Insightful)

      by zippthorne (748122) on Wednesday November 28, 2007 @01:23PM (#21507531) Journal
      No. It will have very little effect on the actual spacecraft itself. However it will provide invaluable data (being only the second instrument ever to make in situ measurements there) to confirm and help update our models.

      No matter what happens, it can't negatively affect the mission, because it is the mission. (well part of the mission, anyway) As a useless analogy, if Space Aliens came down and ray-gunned all of SETI's equipment, you wouldn't say that SETI's mission would be negatively impacted, would you?
    • Re: (Score:3, Insightful)

      by quanticle (843097)

      can this negatively affect the mission/spacecraft itself?

      Technically, the mission was to study the outer planets, so its already been accomplished. NASA keeps listening to Voyager even though its mission is technically complete because its one of a select few probes on course to exit the solar system. In other words, its mission right now is to go to the edge of the solar system and report back what it sees. In this sense, Voyager is close to accomplishing its (2nd) mission.

  • Does it travel back in time/come out the other side/anything else cool, or is it just like hitting a bug on the windshield? News at 11.
    • by HTH NE1 (675604)
      Maybe it receives super ESP powers, creation of matter, exertion of force at a distance, every mental god-like power except for being able to correctly guess someone's middle initial.
  • by schwit1 (797399) on Wednesday November 28, 2007 @12:37PM (#21506905)
    Now that the tailwind has slowed down.
  • by jez9999 (618189) on Wednesday November 28, 2007 @12:38PM (#21506915) Homepage Journal
    There's a Voyager 2?! Oh God no; come back Enterprise, all is forgiven...
    • by VJ42 (860241) *
      Don't worry, that was Voyager 2, Voyager 1 was in the motion picture, remember (and then quickly erase it from your memory again).
  • by Anonymous Coward
    "The boundary of the termination shock is [...] wobbly, fluctuating in both time and distance from the sun"

    Are you SURE that it fluctuates in time from the sun, or do you actually mean that it fluctuates (only) in distance from the sun? Then there's this beautiful piece of prose:

    "... 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. At the termination shock [...] the solar wind is decelerated to less than the
    • I don't understand how this was moderated a troll. You are absolutely correct on every point. I wish my moderator points were active today, I'd at least try to get you back to 0.
    • by Kohath (38547)
      Surely, going from inside to outside, Voyager 2 will have to cross the boundary an odd number of times?

      I was going to ask this same question.

      I wonder what's wrong with the mods who moderated you down?
    • by Remus Shepherd (32833) <remus@panix.com> on Wednesday November 28, 2007 @02:00PM (#21507977) Homepage
      The writeup didn't bother me at all. But then, I *am* a scientist.

      Are you SURE that it fluctuates in time from the sun, or do you actually mean that it fluctuates (only) in distance from the sun?

      The termination shock fluctuates in distance because it's an interaction between the heliosphere of the sun and the interstellar medium. Parts will experience more drag due to magnetic fields, and thus be closer to the sun than other parts of the shock. It fluctuates in time because the sun's output fluctuates in time -- when the solar winds are stronger, the corresponding parts of the termination shock will be further away. So it fluctuates in both time and distance, and depends upon solar activity. Just as the writeup said.

      Ignoring the poor English, care to explain the logic behind this? Surely, going from inside to outside, Voyager 2 will have to cross the boundary an odd number of times?

      Nope. The solar winds overlap each other. A weak wind will create a shock terminator nearer to the sun, while a stronger wind will create one further away. And they hang out there for a long time after they were generated. Apparently the astronomers looked at solar activity and calculated that Voyager 2 will hit two shocks -- one from a weak, but earlier wind and one from a stronger but more recent wind. Makes perfect sense.

      And you have some sort of problem with them describing the terminator shock as the boundary where the solar wind decelerates to the 'speed of sound'? That's accurate. Remember that the solar wind is composed of charged ions, and that we're talking about the speed of sound in a plasma. When the particles go below the speed of sound, then random magnetic fields suddenly become a greater influence than the outward driving force of the sun. There will probably be lots of magnetic turbulence, although nobody really knows what to expect.

      The writeup was technical but accurate as far as I can tell. Sorry it if was too geeky for you.
  • Maybe... (Score:5, Interesting)

    by Dan East (318230) on Wednesday November 28, 2007 @12:40PM (#21506957) Homepage Journal
    Anyone else notice the related stories on the news site?
    Nov. 6, 2003: Voyager Spacecraft Approaches Solar System's Final Frontier
    Dec. 19, 2000: Most Distant Spacecraft May Reach Shock Zone Soon
    May 25, 2005: Voyager Spacecraft Enters Solar System's Final Frontier

    Besides the speculation, will we even know when the boundary is crossed? Do they expect data to indicate a transition, or do we even know if the instruments can detect such a thing?

    Dan East
    • Re:Maybe... (Score:5, Funny)

      by Galaga88 (148206) on Wednesday November 28, 2007 @12:46PM (#21507059)
      Much like killing Rasputin, leaving the Solar System is apparently an ongoing process marked by significant milestones.
    • by igotmybfg (525391)
      I didn't look up those articles, but it's plausible that some of them may be talking about Voyager I, which apparently passed termination shock in 2004. In any case, the termination shock's distance from the sun varies from 75 to 90 AU, depending on solar activity, which is why some are predicting that Voyager II will re-encounter the boundary in 2008 (and possibly beyond).
    • by rucs_hack (784150) on Wednesday November 28, 2007 @01:03PM (#21507297)
      Want to see the actual orbital trajectories of the Voyager probes for yourself in 3d type of thing? Because you can, if you use my nBody modeling software.

      If you go here:

      http://code.google.com/p/nmod/downloads/list [google.com]

      and get the windows installer or linux source for my nbody modeling kit, and then download this:

      http://www.politespider.com/nbo/time_series.zip [politespider.com]

      And unzip it to save you the bother of having to actually generate your own time series (3d time series model of the solar system), which can take a while. You can then watch both Voyager probes follow their orbits (with 24th august 2006 as their starting date), for 20,000 days of travel time.

      This isn't a program with a scrummy easy interface I'm afraid, the viewer is console opengl. But there are instructions here:

      http://code.google.com/p/nmod/wiki/nbview [google.com]

      And it's not too hard once you get the hang of it.

      The orbits do not take termination shock into account, this is pure Newtonian motion. The dataset for the solar system has taken months to put together. It's incomplete, It only has our moon (zoom in for ages with Earth centred and you'll see it), the others have been tricky to get right.
    • by Ruie (30480)

      Besides the speculation, will we even know when the boundary is crossed? Do they expect data to indicate a transition, or do we even know if the instruments can detect such a thing?

      Yes. They are still receiving telemetry from both spacecraft (Voyagers I and II) indicating plasma density, strength of magnetic fields and some other data that I forget.

    • by junglee_iitk (651040) on Wednesday November 28, 2007 @01:16PM (#21507443)
      What you are refering to is Voyager 1. TFA is about Voyager 2. They are two different vehicles.

      <wikipedia href="Heliosphere">
      Evidence presented at a meeting of the American Geophysical Union in May 2005 by Dr. Ed Stone suggests that the Voyager 1 spacecraft passed termination shock in December 2004, when it was about 94 AU from the sun, by virtue of the change in magnetic readings taken from the craft. In contrast, Voyager 2 began detecting returning particles when it was only 76 AU from the sun, in May 2006. This implies that the heliosphere may be irregularly shaped, bulging outwards in the sun's northern hemisphere and pushed inward in the south.
      </wikipedia>
    • Re:Maybe... (Score:5, Funny)

      by ghostlibrary (450718) on Wednesday November 28, 2007 @01:17PM (#21507449) Homepage Journal
      Yep, Voyager has approached the theoretical location of the termination shock often-- and each time, we get to revise our theories and have a better understanding of just how interesting our sun is. The joke among solar physicists is: "Where is the termination shock?" 'Just past Voyager.'
    • Re: (Score:2, Informative)

      by imnojezus (783734)
      Those articles all refer to Voyager 1. This one is about Voyager 2
    • Re:Maybe... (Score:4, Interesting)

      by Howitzer86 (964585) on Wednesday November 28, 2007 @02:53PM (#21508675)
      It would be pretty neat if Voyager 2 suddenly popped up on the opposite side of the solar system. Then we'd have a new barrier to obsess over.
  • I would expect that something called "Termination Shock" would have some dramatic effect on an object crossing it. Is this the case? It doesn't sound like it based on what I read. Sounds like a more appropriate name would be "Subsonic Solar Wind Boundary". But what fun is that?
    • The mechanics definition of a shock is a sudden acceleration/deceleration. It's the sudden stop that kills you in the end of a fall; it's the pressure in the nuclear explosion that bowls over everything. As for termination, I suppose substituting 'Solar wind' would make it a bit clearer. But, termination tends to indicate an end to things, and placed with 'shock' sounds to indicate a boundary of sudden deceleration, where as 'solar wind shock' sounds more ambiguous, in an ironic sort of way.
  • they will be used to get data from voyager 2 on conditions at the edge of the solar system

    however, a wobbly spacetime continuum means that voyager 2 must be running linux
    because the wobbly spacetime is an infinite loop, only linux can escape it in 5 seconds
    but time at the termination shock is slow enough that 5 seconds will be 2 years
  • This is pure, over the horizon, is the earth round or flat, kind of stuff. While no one is expecting anything extraordinary, you never really know until you go and look.
  • Once it gets there and crossing is a non-event, we will see that there is nothing of interest out there. Voyager 2 is just crossing into vast, bleak nothingness.
    • by gstoddart (321705)

      Once it gets there and crossing is a non-event, we will see that there is nothing of interest out there. Voyager 2 is just crossing into vast, bleak nothingness.

      Even if nothing cool or dramatic happens, this isn't a non-event.

      This will be the furthest we've ever flung an object from our planet. The milestone may be more symbolic than anything, but this is actually rather impressive.

      Cheers
      • by Suicyco (88284)
        Voyager 1 is the furthest human object.

        Here is a nice link and a graphic of what is still being explored: http://voyager.jpl.nasa.gov/mission/interstellar.html [nasa.gov]
        • by gstoddart (321705)

          Voyager 1 is the furthest human object.

          Here is a nice link and a graphic of what is still being explored

          Ah, thanks for the correction and the link. I was thinking V2 was going to cross the boundary first. As you say, V1 has already done so and is the furthest human object we've made.

          Cheers
  • hrm... (Score:3, Funny)

    by spottedkangaroo (451692) * on Wednesday November 28, 2007 @01:11PM (#21507391) Homepage
    What is the speed of sound in a vacuum? Kinda existential...
  • by infodude (48434) on Wednesday November 28, 2007 @01:12PM (#21507395) Journal
    It's going to reach the edge of the simulation, where it'll get rendered in lower resolution.
  • I am looking forward to the interstellar probe [nasa.gov] mission, which is specifically designed to explore the interstellar medium.

    Unfortunately it will probably not happen in my lifetime, unless we stop putting in charge of the budget people who think that a talk between a teacher in LEO and school-children on earth is more "inspiring" than fundamental research.
  • by Sebastopol (189276) on Wednesday November 28, 2007 @01:24PM (#21507541) Homepage
    ...it will land with a "kerPLUNK!" into a half full goblet of mead at the foot of Zeus.
  • We will soon be intergalactic litterbugs.
    • by 808140 (808140)
      You mean interstellar, right? Voyager 2 won't be intergalactic for a long, long time...
      • Re: (Score:3, Informative)

        by KiloByte (825081)
        Not ever, actually. It would need to go pretty fast -- the escape velocity needed to escape our galaxy from the vicinity of the Solar system is around 1000km/s.

        We have ever launched 5 spacecraft going fast enough to escape out of the Solar system, at mere 11-ish km/s at the Earth orbit ("-ish" because we cheat a bit using gravitational slingshots).
  • by serviscope_minor (664417) on Wednesday November 28, 2007 @01:51PM (#21507891) Journal
    A termination shock/shockwave/bore/hydraulic jump occurs when the bulk speed of a fluid drops below the wave propagation speed.

    Run a tap in to a flat sink (like a kitchen sink) and you see a circular pattern (if the sink is flat) some distance from around where the water hits the sink. The pattern should have shallow fast moving awater close to where the jst hist the sink, and deeper slower water on the other side of the circle.

    The "jump" where the water goes from fast to slow is the same kind of object as a termination shock. For extra fun, stick an object in the slow water, and see how waves propagate ahead of it (against the flow). Then see how it doesn't happen in the fast water.

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