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It gives me great pleasure to hear about the feat that Voyager 1 achieved. I was wondering if Voyager 1/2 could collide with Asteroids (those,if present, outside our solar system) or any other matter present in its way. Did NASA know exactly what path was Voyager going to follow and the possible collisions it could encounter in its journey till date? Could there be any unforeseen object in its path?

Hobbes
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bluelurker
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2 Answers2

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The Voyager probes are outside the Kuiper belt now, and have a very long way to go before entering the Oort cloud. They are now in a place that is almost completely devoid of matter. Or at least I couldn't find any estimates as to how dense the solar system is there.

But what about when they where still in the Kuiper belt?

If Wikipedia is to be believed, the Kuiper belt has a mass of about 4.59*10^23kg and is mostly made of ice. Let's say the average object is a sphere with a diameter of 1m (put in a better estimate, if you want to). An ice sphere of 1m diameter has a mass of 489kg, meaning there are 9.385*10^20 such objects. Each has a cross section of 0.785m^2. Let's say for simplicity, the Kuiper belt is a torus with a major radius of 40AU and a minor radius of 10 AU. (I haven't found a good number for the north-south dimension of the Kuiper belt, sorry). That means that it's volume is 2.64*10^37m^3. That means there is an average free volume of 2.81*10^16m^3 per object.

We can borrow from gas kinetics to get an average free path length, that the Voyagers can fly before colliding with something. (I know this doesn't directly answer your question, but it gives us an idea)

$$ \lambda = \frac{1}{n\sigma} $$ with $\frac{1}{n}$ the mean free Volume and $\sigma$ the average cross section.

We get: drum whirl

239 282.67 AU

Meaning that the voyager probes could almost fly through the Kuiper belt all the way to alpha centauri before smashing into anything. Now keep in mind that material density is much lower where they are right now...

Rikki-Tikki-Tavi
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    The Kuiper belt is probably by far thinner than a torus, so let's say the the result has an error bar of 2 orders of magnitude or so. Doesn't change the fact that smashing into anything has lottery odds. – Rikki-Tikki-Tavi Aug 06 '14 at 10:06
  • Interesting numbers -- but shouldn't large relative velocities increase the probabilities somewhat? – Erik Dec 18 '14 at 05:39
  • @Erik Why should it? The amount of mass is still the same, they are just moving relative to each other. The odds that an object is moving away from the spacecraft's path would seem, intuitively, to be equal to the odds that an object is moving toward the spacecraft's path (is moving on an intersecting trajectory). – user Dec 18 '14 at 09:20
  • Imagine you are crossing a road. Your example assumes the cars are stationary. So you have a pretty good chance of getting across without running into a car. However, the faster the cars are moving, the more likely you will be hit. – Erik Dec 18 '14 at 15:39
  • @Erik, The formula for the free path length comes from gas dynamics. The gas molecules are also in motion. The mistake I make is assuming, that the voyager probes are points, but since the statement I make is about orders of magnitude, not precise values, I think this is not a problem. – Rikki-Tikki-Tavi Dec 18 '14 at 16:32
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    I agree that the effect is probably small. I think though, that the key difference between gas dynamics is that the velocities of the objects won't be random. Rather, they will all tend to be in similar orbits. An interesting problem and your approach is insightful. – Erik Dec 18 '14 at 16:40
  • @Erik Yes, you're right, that is a variable I hadn't considered. I'm not sure it matters, though. This is something better discussed with two beers, a pen and some toilet paper ;). – Rikki-Tikki-Tavi Dec 18 '14 at 17:16
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    Lovely analogy! +1 – Caterpillaraoz Jan 24 '18 at 09:35
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The probability of Voyager colliding with any matter any time soon is unknown, but likely small.

We have no way of detecting small outer solar system objects, because they are small and far away. Therefore, we don't know how many of those bodies there are, and thus we cannot begin to estimate the probability quantitatively. But, space is big, so in all likelihood we can say that the probability is very small.

gerrit
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  • thanks for the answer.I guess NASA must have prepared for such events . – bluelurker Jul 28 '14 at 14:59
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    NASA cannot really do much to prepare for such events. The Voyager spacecrafts are long, long beyond their designed lifetime. Anything that happens now (and has for a long time) is bonus. In the unlikely event that a body impacts Voyager, NASA will lose contact and will likely not know for sure what has happened. – gerrit Jul 28 '14 at 15:00
  • Are there reasons to believe that the density of dust particles/micrometeoroids is higher slightly outside of the heliopause? – LocalFluff Jul 28 '14 at 17:38
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    Alternatively, the likelihood of Voyager colliding with matter is actually high, given enough time, however the period of highest likelihood has passed. I am trying to find documentary evidence on how much damage has been incurred so far due to collisions with micrometeorites etc. – Rory Alsop Jul 28 '14 at 23:55
  • @RoryAlsop I see your point. Let's say that the likelihood of it colliding during the time that we are able to communicate with it at all is small. Integrated over millions of years the chance of collision might not be very small. – gerrit Jul 29 '14 at 14:09
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    @gerrit yes it is. Do the math. Interstellar space is very empty. If there was a significant amount of material there, we would see that by it's gravitational influence on the galaxy (the way we see dark matter). Take my calculation and plug in the numbers for interstellar space. You will see, that the chance of them hitting anything is zilch. – Rikki-Tikki-Tavi Aug 06 '14 at 10:14
  • @Rikki-Tikki-Tavi So we can estimate the total mass, but how is that mass distributed over different sizes of particles? – gerrit Aug 06 '14 at 14:56
  • @gerrit Well, if there were a large amount of objects in interstellar space that pose a collision hazard, we would occasionally see them whizzing through our solar system at speeds much above the sun's escape velocity. But we don't. What we do see, are cosmic dust particles, but they are to small to count as a "collision" to me. But yes, the voyager probes are catching some of those, certainly. – Rikki-Tikki-Tavi Aug 06 '14 at 15:31