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Voyager craft exits the Solar System...

voyager extra-solar

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#31    Taun

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Posted 25 March 2013 - 01:41 PM

View PostWaspie_Dwarf, on 23 March 2013 - 12:04 PM, said:

That would be a very arbitrary definition, as it would depend entirely on which direction you are heading in.

While I completely agree with you on this... right now aren't ALL of our definitions on this a bit arbitrary?...  Perhaps the last gift Voyager can give us is forcing the scientists to finally pin down exactly where the solar system ends - and what defines the limits....  Perhaps we could call it the "Voyager Line"...


#32    Frank Merton

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Posted 25 March 2013 - 01:59 PM

I'm not sure what it is but it seems he finds something to nitpick with everything I post.  If he thinks about it awhile maybe he will realize it isn't all that arbitrary -- that once you've gotten about halfway from Sol to whatever is in that general direction, you will be out of the solar system.


#33    Waspie_Dwarf

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Posted 25 March 2013 - 02:48 PM

View PostTaun, on 25 March 2013 - 01:41 PM, said:



While I completely agree with you on this... right now aren't ALL of our definitions on this a bit arbitrary?...  Perhaps the last gift Voyager can give us is forcing the scientists to finally pin down exactly where the solar system ends - and what defines the limits....  Perhaps we could call it the "Voyager Line"...
The heliopause isn't an arbitrary definition of the edge of the solar system, it is measurable. It is the point at which particles from the interstellar wind are greater in number than the particles from the solar wind. The argument between scientists is over whether this is what Voyager has in fact measured.

The problem with this definition is that it fails to take into account that there are believed to be objects orbiting the sun at considerably greater distance than the heliopause. Comets travel much further than this and the Oort cloud, whilst orbiting the sun, would be regarded outside of our solar system.

So the Sun's gravitational influence extends far beyond the influence of the solar wind. Why can we not define the point at which the Sun's gravitational influence ends as the edge of the solar system? keithisco has already hit the nail on the head with this one. Technically, the Sun's gravitational influence extends for ever. It gets weaker according to the inverse square law (if you double you distance you only feel one quarter of the gravitational pull, triple your distance an you only feel one ninth of the pull, and so on). So in terms of gravitational influence there really is no clearly definable edge.

View PostFrank Merton, on 25 March 2013 - 01:59 PM, said:

I'm not sure what it is but it seems he finds something to nitpick with everything I post.  If he thinks about it awhile maybe he will realize it isn't all that arbitrary -- that once you've gotten about halfway from Sol to whatever is in that general direction, you will be out of the solar system.
Don't take it so personally.

The very nature of good science is to question and find fault rather than accept without question. I believe in good science. I don't believe that something should be accepted as fact without being questioned. If the case put forward can not withstand questioning then it wasn't a worthwhile case to begin with.

It is in that vein that I put forward these problems I have with your definition.

Picking "half way to the nearest star" as the edge of the solar system is, in my opinion, a very unsatisfactory definition. It would vary from star to star, with almost identical stars having totally different sized solar systems based purely on how close another, totally unrelated, star was. By your definition our solar system extends 2.21 light years. But that of Alpha Centauri B (which is known to have an earth sized planet) can be as small as 5.6 AU, which is only slightly greater than the distance between Jupiter and the Sun.

Since stars are not stationary the size of a solar system will dramatically change over time as other stars pass by Proxima Centauri will not always be the closest star to the Sun. The distance to the nearest star is not always going to be 4.24 light years.

Worse still, stars within binary systems have been found to have planets. How does your definition work here when the stars are in highly elliptical orbits around each other? Do we have a solar system which varies in size from week to week or do we have a special rule that states that the average distance between them applies?

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#34    Frank Merton

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Posted 25 March 2013 - 02:50 PM

Stars are distributed somewhat randomly, so as you get further out the chances of some star being closer to Sol increase even if it is not directly in your path.


#35    danielost

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Posted 25 March 2013 - 03:04 PM

Looks like we are going to just draw a line in space and call it the edge of the solar system.  Kind of like we do with borders on earth.  Which is why so many riversd are part of said border.  Gives us something to see.



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#36    Waspie_Dwarf

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Posted 25 March 2013 - 03:59 PM

View Postdanielost, on 25 March 2013 - 03:04 PM, said:

Looks like we are going to just draw a line in space and call it the edge of the solar system.  Kind of like we do with borders on earth.  Which is why so many riversd are part of said border.  Gives us something to see.
Yes and no.

What Voyager is looking for is the start of interstellar space. It is a measurable thing. We could take the same instruments and find the heliopause around other stars, so it is a reproducible measurable definition of the edge of the solar system based on sound scientific principles. It is the sort of definition scientists like.

As I said though, this is not the only definition of the edge of the solar system as there are objects measuring the sun at a greater distance. A good, common-sense definition of the edge of the solar system would, therefore, be the greatest distance from the Sun attained by an object in orbit around it. This definition could be applied equally to all stars, and would have one advantage over Frank's definition in that a star with no objects around it would have no solar system by this method. Frank's method give an edge to a solar system even for stars with out planets, asteroids, comets etc.

Just to show that I'm at least consistent I will now nit pick my own definition.

There is however a massive problem with my definition, or, to be be honest, two massive problems. The first is the fact that at the moment we don't have the ability to see objects in the Oort cloud. We simply can not detect objects that small that far away from the Sun. This in itself is not a killer blow, after all until it is confirmed that Voyager has passed through it we don't know exactly where the heliopause is.

The bigger problem is this: logically we can never know that we have found the edge of the solar system. We can never be sure that we have found the furthest object in the solar system. There are millions of objects out there and if we spent a billion years searching for them we could never be absolutely certain that we had found every single one. Again. I don't think this is a killer blow, it would just have to be referred to as "knowm edge of the solar system".

Another issue with my definition is one which is not specific to this issue, but crops up all across astronomy at the moment, how big does and object be to considered a solar system object?

For an example of what I mean, look at Saturn, it has 62 known moons. But the rings are made up of thousands of tiny objects all orbiting Saturn. Larger objects orbiting within the rings Are considered moons, but the tiny particles aren't. At the moment common-sense is enough to distinguish the two, but as we find smaller and smaller moons we are going to reach a stage where we have to answer the question how small can an object be before it is no longer a moon? The answer is almost certainly going to be unsatisfactory and arbitrary.

Arbitrary definitions, just picking a limit, are not scientifically satisfactory (this is my problem not just with Frank's definition, but with many issues currently occurring in astronomy at the moment) however, sometimes, they are all we have got.

Edited by Waspie_Dwarf, 25 March 2013 - 04:44 PM.
typo.

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#37    Waspie_Dwarf

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Posted 25 March 2013 - 04:43 PM

Just after I made my last post I came across this article on the Discovery site which says a lot of what I was trying to say (only a lot more eloquently):


Where's the Edge of the Solar System? It's Complicated...


news.discovery.com said:

If you thought finding a definition for Pluto was contentious, try defining the edge of the solar system.

A press release from the American Geophysical Union (AGU) last week announced that on August 25, 2012, NASA’s Voyager 1, officially entered interstellar space. This milestone comes after speeding across the solar system for 35 years following its landmark flybys of the Jovian and Saturnian system. The AGU release title read: “Voyager 1 Has Left The Solar System, Sudden Changes In Cosmic Rays Indicate.”

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The last paragraph is especially relevant:

Quote

Whatever you call solar system’s edge, there doesn’t seem to be a consensus among scientists. Voyager’s bold entry into interstellar space may happen in the near future, or perhaps not until the year 20,000 A.D.  – depending on your definition.


"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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#38    danielost

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Posted 25 March 2013 - 05:43 PM

Looks like we have to take it on one at a time, allowing room in our discription to change when needed.  Becausde using your defintion the centary system would be about 1/2 a ight across.

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#39    Waspie_Dwarf

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Posted 25 March 2013 - 06:12 PM

View Postdanielost, on 25 March 2013 - 05:43 PM, said:

Looks like we have to take it on one at a time, allowing room in our discription to change when needed.
No, the opposite is true. We need a definition which is standard and which can be applied equally to all systems. Both mine, and Frank's definition pass that rule.

View Postdanielost, on 25 March 2013 - 05:43 PM, said:

Becausde using your defintion the centary system would be about 1/2 a ight across.
I assume you mean Alpha Centauri system.

If you are talking about my definition (as opposed to Frank's) then the figure would be about 0.4 light years across, since Alpha Centauri C (Proxima Centauri) orbits at a distance of 0.2 ly from the system barycentre.

Why is this a problem? What is wrong with that figure?

Bear in mind that I specifically pointed out that my definition would give a known limit to the edge of a solar system and not an absolute one. Given that Proxima is the furthest known object orbiting the Alpha Centauri system you seem to be making my point rather well.

"Space is big. Really big. You just won't believe how vastly, hugely, mind-boggingly big it is. I mean, you may think it's a long way down the street to the chemist, but that's just peanuts to space." - The Hitch-Hikers Guide to the Galaxy - Douglas Adams 1952 - 2001

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