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View Full Version : Would Pluto and Neptune ever crash?



The_Radiation_Specialist
2007-Oct-02, 05:07 PM
I was simulating a few thousand years of solar system orbits with Sky View Cafe and noticed that the orbits change a lot during a few millennium.

Pluto (the former planet) and Neptune's orbits gets very close and they cross over at times, so :

Assuming we give it billions of years, is it possible for Pluto and Neptune to crash?

Is our measurement of positions/speed accurate enough to predict such a crash?

The gravity might also play a role and prevent the two from crashing, how would that work? Can we predict that it would "never" crash?

And finally if they do crash what can we expect? Would earth be in any danger?

John Mendenhall
2007-Oct-02, 05:13 PM
As I recall, and without checking the references, I think Pluto and Neptune are in resonant orbits and won't collide. But, to quote Charles Barkely, "I could be wrong."

Saluki
2007-Oct-02, 05:21 PM
FWIW, this supports John (and my) recollection.

http://www.astronomycafe.net/qadir/q364.html

grant hutchison
2007-Oct-02, 06:04 PM
All these programs become less accurate the farther you run them from the present day, and this is particularly so for the orbit of Pluto.
In particular, for Sky View Café (http://www.skyviewcafe.com/skyviewhelp.php#accuracy):

Pluto is covered by Meeus' adaptation of the work of Aldo Vitagliano. The accuracy of the given method is said to be quite high, better than one-tenth of an arc second, but only for the years 1885-2099. I have no idea how much error creeps in outside of that time span, but I have made no effort to limit viewing Pluto to this range of years, so keep in mind that, beyond that span of time, I'm using the formula outside of its recommended range.
Like John Mendenhall and Saluki, my understanding is that the 2:3 resonance between Neptune and Pluto (as well as the other Plutinos) prevents them ever being in the same place at the same time.

Grant Hutchison

The_Radiation_Specialist
2007-Oct-02, 06:23 PM
Thanks for the answers.

But in the hypothetical situation that they "do" crash what might we expect on earth? What would happen to Neptune?

astromark
2007-Oct-02, 06:23 PM
Forever is a very long time... To say these planets will not or can not collide is on the fringe of reality. If these objects cross each others path then yes they could theoretically be in conflict. The question then is. Do they?

Your last point regarding the Earth being in any danger. Probably not. Pluto is smaller than our moon and Neptune is a gas giant. Considerable disruption to these planets would not effect Earth in any way.
Astrologers would need to rewrite their charts...:)

Saluki
2007-Oct-02, 06:43 PM
The question then is. Do they?

I have been trying to dig up a graphic that shows it clearly, but I am fairly certain tha the orbits do not intersect. If you look at a 2d representation of the 3d orbit it does indeed look like they intersect at 2 points, however, in the real 3d situation, pluto is well away from Neptune's orbit at the points where it appears to cross on the 2d drawings.

Edit: This one shows it somewhat well. You can see that the orbit of Pluto is actually outside the orbit of Neptune at the points where they appear to intersect in most renderings.

http://www.daviddarling.info/images/Pluto_orbit.gif

grant hutchison
2007-Oct-02, 07:29 PM
I have been trying to dig up a graphic that shows it clearly, but I am fairly certain tha the orbits do not intersect.Here (http://www.ghutchison.pwp.blueyonder.co.uk/orbits/pluto.jpg)'s one I prepared earlier. :)
It's a shallow diagonal view from north of the ecliptic, prepared in Celestia, showing that when Pluto crosses through the plane of Neptune's orbit, it's still well outside the orbit of Neptune. It only moves closer to the sun than Neptune when it is well to the ecliptic north.

Grant Hutchison

tony873004
2007-Oct-02, 07:38 PM
I simulated their orbits, and wrote a short article for my website about the simulation and their 3:2 resonance: http://www.orbitsimulator.com/gravity/articles/pluto.html . There's an animation on this page that shows Neptune virtually "repel" Pluto's advancing orbit in a rotating frame anytime it gets too close.

In addition to this 3:2 resonance, there's also a resonance involving their inclinations. Although no info on this resonance is included in my article, I think this is how it works: If Pluto were to cross Neptune's distance while it and Neptune were at the same true longitudes in their orbits (which can't happen due to the forementioned 3:2 resonance), they still would not collide because Pluto, with its high inclination, would be either high above or far below Neptune's position. As Pluto's nodes precess with time, and/or its inclination fluxuates, lowering the angle between its orbital plane and Neptune's, potentially bringing its ascending and decending nodes with respect to Neptune's orbital plane dangerously close to Neptune's position, Neptune should also repel the precession, and/or advancing inclination, so even over eons of time, they will never come close. Don't trust that I got this completely right, but it's an easy Google to get a better explanation of this additional resonance.

Ilya
2007-Oct-02, 08:45 PM
Your last point regarding the Earth being in any danger. Probably not. Pluto is smaller than our moon and Neptune is a gas giant. Considerable disruption to these planets would not effect Earth in any way.


Pluto's mass: 1.3 * 10^22 kg
Neptune escape velocity: 23500 m/sec
Resulting kinetic energy, to 2 sig. digits: 3.6 * 10^30 J
Sun's energy output: 3.9 * 10^26 J/sec

The impact would produce almost as much energy as Sun emits in 10,000 seconds and would last about 100 seconds -- the time it takes for Pluto to travel its own diameter at that speed.

So for about 100 seconds Neptune would be 100 times brighter than Sun. But at 30 AU from Earth, that would shrink to 0.1 as bright as Sun. Being a point source, it will probably do serious retinal damage to anyone looking at it, but that's about the extent of effects on Earth.

Until debris starts hitting 80 years later :)

rtomes
2007-Oct-04, 01:01 AM
The best long term calculations of the solar system motion are now believed to be accurate for about 20,000,000 years into the past and future. Pluto is still there for all of that time. These calculations are now so accurate that one of the Milankovitch cycles of 405,000 years is now used as the primary means of accurate dating of geological formations for the last 23,000,000 years.

RalofTyr
2007-Oct-04, 02:10 AM
What would be cool if Neptune disrupted Pluto's orbit, sending it inward towards the sun and creating a comet like orbit with, possible, the largest comet ever witnessed.

tony873004
2007-Oct-04, 02:52 AM
The best long term calculations of the solar system motion are now believed to be accurate for about 20,000,000 years into the past and future. Pluto is still there for all of that time. These calculations are now so accurate that one of the Milankovitch cycles of 405,000 years is now used as the primary means of accurate dating of geological formations for the last 23,000,000 years.

There are certain properties of orbiting bodies that remain accurate even longer than that, and I would guess that stable resonances are one of them. But I would doubt that we can tell with any certainty where in its orbit any of the planets will be in 20 million years, or even 2 million years. Each orbit's size, shape, and orientation can be described by 5 orbital elements, and these elements are know to oscillate over long periods of time due to perturbations primarily by the other planets. If we know for example that Earth's inclination varies periodically by 3 degrees, then we always know its inclination to within 3 degrees. Similarily, if we know that a planet's semi-major axis varies in cycles by 100,000 kilometers, then we will always know to within 100,000 kilometers the planet's average distance to the Sun. But if our knowledge about a planet's semi-major axis is off by even 1/100 of 1 percent, then its period is off by this amount ^(3/2), so its known position in its orbit begins to drift, changing its 6th orbital element, mean longitude, in a linear rather than a cyclic fashion. Unlike the error in the other orbital elements, this error builds, orbit by orbit. After a few thousand years, we may be able to accurately predict an orbit's size, shape, and orientation, but exactly where the planet will be in its orbit will not be known.

The ~400,000 year eccentricity cycle isn't exact. It definately jumps out at you when you look at a graph, but sometimes it might be only 398,000 yr, while at other times it be 409,000. I don't have any doubt that we can accurately say that in 20 million years the Earth will still have its ~400,000 cycle, but whether we are at a minima or maxima on this trend would not be known. It's similar to not adjusting a clock for a few years (assume the batteries are good the whole time). I can tell you with confidence that the minute hand will still be going around once per hour, but because of small errors in the clock's precision, I would be doubtful that it would be displaying the correct time.

So even though I might not have a clue as to where Neptune will be in 2 million years, because of the resonance, I can confidently say that Pluto won't be anywhere near it.

Neverfly
2007-Oct-04, 03:10 AM
What would be cool if Neptune disrupted Pluto's orbit, sending it inward towards the sun and creating a comet like orbit with, possible, the largest comet ever witnessed.

You mean like Sending Venus in at us while it is spewing influenza all over the place?:doh:

John Mendenhall
2007-Oct-04, 05:03 PM
You mean like Sending Venus in at us while it is spewing influenza all over the place?:doh:

This idea will never fly.

Celestial Mechanic
2007-Oct-04, 07:28 PM
You mean like Sending Venus in at us while it is spewing influenza all over the place?:doh:
Homer Simpson: Manna! Mmmmmm...... ;)

frankuitaalst
2007-Oct-05, 06:25 PM
Herunder an animated gif showing the outer planets . The gif was generated using the JPL Near Earth Asteroids site , with descending point of view .
It's clear that the orbits do not intersect .

JohnD
2007-Oct-05, 09:41 PM
Astrologers would need to rewrite their charts...:)

But they do, and have done ever since planets more distant than the naked eye ones were discovered.
Doesn't worry them at all.
Bit like sub-atomic physics - "Ah! There are even smaller(distant) particles(planets)! That explains why my predictions are a bit off!"

John

KaiYeves
2007-Oct-06, 05:39 PM
Pluto is still a planet, it's just a dwarf planet and not a regular one.

grant hutchison
2007-Oct-06, 07:22 PM
Pluto is still a planet, it's just a dwarf planet and not a regular one.According to the IAU resolution, a dwarf planet is not a planet. (Some people object to the grammatical logic of that construction, but that's another matter. :))

Grant Hutchison

KaiYeves
2007-Oct-06, 07:53 PM
That's what I meant, it still has planet in the name.

tony873004
2007-Oct-06, 10:06 PM
(Some people object to the grammatical logic of that construction, but that's another matter. :))

Like me! I just assumed "dwarf"=adjective, "planet"=noun

If we take the IAU literally, is Earth still a planet? "A planet is a celestial body that..."

Neverfly
2007-Oct-06, 10:15 PM
In that case...

Jupiter, Saturn, Uranus and Neptune aren't really planets. They are more like really really really big gas bubbles.

Maybe Cosmic farts.

grant hutchison
2007-Oct-06, 10:28 PM
That's what I meant, it still has planet in the name.I assumed your post was in response to the OP's use of the phrase "former planet". I was pointing out that "former planet" is an accurate enough description, despite the new terminology. If you meant something else, then I apologize.

Grant Hutchison

KaiYeves
2007-Oct-07, 02:58 AM
It was in response to the OP. I wrote a great and geeky essay about public and media reactions to the Pluto controversy. It included relevant quotes from Jurassic Park, X-Men, High School Musical, Pale Blue Dot, and Star Wars: The Phantom Menace. They were all, believe it or not, related to a central theme you may be able to guess at. (Hint: it's also a major theme in X-Men) If you'd like to see it, just ask.

Neverfly
2007-Oct-07, 03:04 AM
Asks.

laurele
2007-Oct-07, 05:02 AM
Like me! I just assumed "dwarf"=adjective, "planet"=noun

If we take the IAU literally, is Earth still a planet? "A planet is a celestial body that..."

This is exactly why the IAU definition makes no sense. The term dwarf planet is an adjective modified by a noun, not a "compound noun," as those who voted for this definition claim. Dwarf stars are still a subclass of stars; dwarf galaxies are still a subclass of galaxies. Saying a "dwarf planet" is not a planet at all is just plain ridiculous and amounts to the IAU concocting its own grammar to fit a specific agenda.

Why should we accept that the vote of four percent of this organization changes reality and somehow makes Pluto less than a full fledged planet? Even members of the IAU state that they have no authority to impose their decision and that no one is bound to accept it.

Hopefully, at their next General Assembly, the IAU will revisit this issue and do a better job with the definition. Passing the resolution that failed, the one that placed dwarf planets as a subclass of the broader term planets would be a good start.

grant hutchison
2007-Oct-07, 12:49 PM
This is exactly why the IAU definition makes no sense.As I said, that is "another matter": off-topic for this thread.
Please don't hijack other people's threads in order to pursue your own agenda.

Grant Hutchison

laurele
2007-Oct-07, 10:54 PM
My apologies; I did not see myself as "hijacking" this thread, as the planet vs. dwarf planet issue had already been raised in previous posts.

To KaiYeves: No, we have not "known" for the past 12 months that the answer is eight planets. We've known that some people view the solar system this way while others do not. As an opponent of the IAU decision, I can tell you that my position is not based on fear of change but on the many problems with both the process that led to the change and the actual result. I don't believe people should simply accept change for change's sake, especially when they have researched the issue and genuinely come to the conclusion that the change is a step in the wrong direction and when other professionals in the field agree that the change creates more problems than it solves.

The argument that "keeping Pluto would lead to a large and tangled solar system that would be a burden for students to remember" is hardly a scientific one. Nature is not "designed" so humans can have easy classification systems. If there are 200 planets in the solar system, then that's what there are, regardless of the implications for teaching them. Actually, memorizing their names is less important than understanding the concepts of what the gas giants, terrestrial planets, ice dwarfs, satellites of planets, etc. are.

Supporting the planet status of Pluto, Eris, Ceres, and other KBOs that have achieved hydrostatic equilibrium is not the equivalent of "looking back." On the contrary, it is looking forward to an expanded and broadened view of our solar system, and in eight years, valuable new information from both the Dawn mission and New Horizons.

grant hutchison
2007-Oct-07, 11:23 PM
My apologies; I did not see myself as "hijacking" this thread, as the planet vs. dwarf planet issue had already been raised in previous posts.Well, it sure is heading in a new direction, which is just the same old direction. :(
Adieu.

Grant Hutchison

antoniseb
2007-Oct-07, 11:39 PM
The dwarf planet issue has nothing to do with the celestial dynamics issue of whether Pluto and Neptune might someday collide. Please stay on topic.

KaiYeves
2007-Oct-08, 02:16 AM
Sorry. I wasn't posting the essay to argue, only because Neverfly asked.

Neverfly
2007-Oct-08, 02:34 AM
I second that:D

KaiYeves
2007-Oct-08, 02:56 AM
By the way, did you like it?

Neverfly
2007-Oct-08, 03:03 AM
By the way, did you like it?

Yes, but you neglected Mickey Mouses response to this.

However, since we have determined that Pluto will not collide with Neptune, perhaps in time Pluto can rise again to challenge his status.;)

phaishazamkhan
2007-Oct-09, 02:02 AM
Neptune hasn't cleared its orbit because Pluto still crosses it. Apparently some orbits are clearer than others in the eyes of the IAU.

astromark
2007-Oct-09, 07:13 AM
The point being...?

No it would appear that they do not cross each others path. Nor will they any day soon. Pluto the dwarf planet does come inside the orbit of Neptune, but not at the point they are closest together. My source for this startling revaluation is 'Starry Night.' By running it fast and setting the date forward. No conflicting intersection was found. Potentially It is possible that through some sort of movement due to the gravity of Jupiter or progression of either orbital track. Then yes its still possible for these planets to collide. If you want excitement from astronomy then study the red stars and Omega Cent., Looking to Pluto for action is a wast of your time.

mugaliens
2007-Oct-12, 02:54 PM
The point being...?

No it would appear that they do not cross each others path. Nor will they any day soon. Pluto the dwarf planet does come inside the orbit of Neptune, but not at the point they are closest together. My source for this startling revaluation is 'Starry Night.' By running it fast and setting the date forward. No conflicting intersection was found. Potentially It is possible that through some sort of movement due to the gravity of Jupiter or progression of either orbital track. Then yes its still possible for these planets to collide. If you want excitement from astronomy then study the red stars and Omega Cent., Looking to Pluto for action is a wast of your time.

Actually, not, Astromark, for the orbits of these two are actually self-stabilizing, much like Lagrange points. If either is moved a little bit, the other naturally tends to settle back into the current orbit.