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Voyager 2 Set to Reach Termination Shock
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."
this is the kind of thing scientists predict all the time and observe in lab experiments... but this device is actually GOING to the edge of a solar system... it's someplace human made instruments haven't been. Science at it's very purest form, simply going and observing something nobody has actually seen before.
Why do you go on vacation to foreign places.. aren't postcards and Discovery channel good enough? It's a whole lot different to say "we were there" than guessing what it would be like from a long distance.
There's a Voyager 2?! Oh God no; come back Enterprise, all is forgiven...
== Jez ==
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It means Janeway's going to have to pretend to be thrown all over the place while bits of the ship fall off.
ccalam - acoustic versions of new songs.
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
Better known as 318230.
No, it is not. It is the interstellar medium. Read: termination shock.
Space is not a vacuum. The speed of sound in space is about 100 km/s, according to Wikipedia.
http://library.thinkquest.org/C0126626/fate/fate%20of%20universe.fate%20of%20universe.mass%20density%20of%20the%20universe.htm
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?
The Christian Right is Neither (Christian nor right). See: Matthew 23, Matthew 25, Ezekiel 16:48-50
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.
So, in space, they can hear you scream?
sudo eat my shorts
Why do you go on vacation to foreign places...
OMG, underage Taiwanese hookers...in space?I swear to God...I swear to God! That is NOT how you treat your human!
Four, just four small space probes.
Sorry dude, all the space ships you see on TV are just FX. We are not (yet) exploring the galaxy. Will we get any new data about "termination shock" or whatnot? Yeah! We may confirm that there exists this termination shock we expect to find there, or we may find our theories are wrong and there is not such "thing".
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
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
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
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.
See, space is not empty
It's full of stars...
Once to get outside the boundary, twice if the boundary expands and catches back up with it, and thrice to once again get outside the boundary.
Just a thought.
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It's going to reach the edge of the simulation, where it'll get rendered in lower resolution.
-- Only information exists, the rest is just smoke and mirrors.
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>
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?
Can you be Even More Awesome?!
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:
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.
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.
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.
SJW n. One who posts facts.
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.
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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.
Europeans in general don't understand this, and it's probably true for most of the rest of the world. From where I live I can make it to Mexico in about 12 hours of solid driving, or to Canada in about 20 hours, but in most places in the US it's a day or more of travel time to either country. In most of Europe you can be to another country in an hour or two. Now, I've lived in both Italy and Germany (for about a total of 5 years of my life), and when I'd be talking to people, they'd talk about wanting to travel to the US and all the places they'd like to see. Want to see LA, San Francisco, New York, New Orleans, Grand Canyon, Yosemite Valley, Yellowstone, etc., and expect they could manage this in about two weeks, which, by comparison, is like wanting to travel from Moscow to London and hit all the major points in between in that kind of time frame.
The reason why many Americans speak only one language or don't spend a lot of time in other countries is based in this. For a majority of Americans there is only one language besides English that is of any utility, and that is Spanish. I was once fluent in both German and Italian, but since I've been back in the US I have yet to run into a situation where I needed to speak either language. It's not like we can day trip to France or that most businesses can deliver finished products to a foreign country with a simple truck ride of 3 or 4 hours.