1st or only in our galaxy?

Thanks for the graphs.. I was just trying to draw this on a piece of paper, but it didn't go too well..
 
Janus58 said:
Just for clarification here are two graphical representations of heliocentric paths of moon orbits, the first is of Luna:
moonorb.jpg

...The white arc represents the Earth-Luna system path and the yellow line the Moon's path. Here it is easy to see that the moo'n's path remains concave to the Sun...
Thanks - if you did not cheat, you won the argument easily. Even if you did, you sure made your point very clearly.

You have also partially answered my first of two questions. I.e at least with a separation a significant fraction of the current Earth/Moon separation any mass circling (not "orbiting") Earth at a fixed distance is not a satellite of the Earth, but part of the Earth / Moon dual planet system. Since you made the graphs so quickly will you repeat it again but with the moon at the Roche limit. This will answer my new question below:

Has the Moon ever been a satellite of the Earth?

You comments on the original questions would be appreciated also.
 
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Billy T said:
Thanks - if you did not cheat, you won the argument easily. Even if you did, you sure made your point very clearly.

You have also partially answered my first of two questions. I.e at least with a separation a significant fraction of the current Earth/Moon separation any mass circling (not "orbiting") Earth at a fixed distance is not a satellite of the Earth, but part of the Earth / Moon dual planet system. Since you made the graphs so quickly will you repeat it again but with the moon at the Roche limit.
Unfortunately, the Roche limit for the moon is so slose to the Earth that I can't keep enough of the orbit in the image while still being able to resolve the two paths well enough to see anything.

This will answer my new question below:

Has the Moon ever been a satellite of the Earth?
As long as the Moon was ever closer than 260,000 km, yes.(Assuming that we define a satellite as a body that is more greatly attracted to the Earth than it is to the Sun.)
You comments on the original questions would be appreciated also.

Okay.

(1) Beyond what constant separation form the Earth, if any, does a satellite become a planet?

(2) Has man ever made a planet that with Earth constitutes a dual planet system?

1. 260,000 km. With the caveat that I wouldn't consider just any body greater than that distance as a "planet" . To be considered a planet I would expect the body to be massive enough that gravity is the major factor in the shape it takes. (IOW, large enough to be pulled into a spherical shape by its own gravity.)

2. With the above caveat about waht would constitute a planet, I do believe that there is at least one man-made object that could be locked in a sychronized solar orbit with the Earth.
In 2002, An object was discovered that was thought could be a another moon of the Earth. It turned out to be a booster from the Apollo 12 mission. It had been in Solar orbit unitil it recently was recaptured by the Earth.
 
to Janus58:

We seem to have three different definitions, in only this thread, of what a satellite is:

(1) Mine (from a prior post implicitly gives one whle it defines what a dual planet system is):
“If the orbits of two bodies orbiting their star are both always concave towards the star, but each can sometimes be closer to the star than the other, then they constitute a dual planet system, and neither is a satellite of the other.” (The “but…” condition is required to keep, for example, Earth and Mars from being a dual planet system.)

(2) Dinosaur’s (also from prior post of this thread):
“If you superimpose a plot of a true satellite on its planet’s orbit, you see loops…”

(3) And yours:
“we define a satellite as a body that is more greatly attracted to the Earth than it is to the Sun. … plus the additional requirement that self gravity should make it roughly spherical“ - Be careful the little planet people may take you to court for discrimination based on size :eek:

Certainly yours is the easiest to apply, but I prefer mine as with it the moon is not both a satellite and a planet as it is with yours. I would like to suggest that Dinosaur's be adopted as the definiton of a NEO satellite, but that is no good if geo-stationary satellites can show loops.

Thanks for the answer to my second of two questions, but that leads me to ask: How did Earth capture the spent rocket in a two body inter action? ( I am assuming from your statement “It had been in Solar orbit until it recently was recaptured by the Earth“ that it was for some period not bound to the Earth. I.e. how did it get bound with negative potential again?) Perhaps it is not again bound to the earth - that could be the case if it is at one of the two stable Earth/sun Lagrange points, but if it is there Jupiter will surely set it free soon as those points are not very deep "holes."
 
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Janus58: Thanx for correcting me. Your analysis seems valid.

I was surprised by your diagram of Callistro’s orbit. I thought that Luna was the only satellite in the solar system which does not have “loops” in its orbital path.

Now that you have mentioned it, I realize that a satellite can reverse direction relative to its planet’s orbital path while always traveling in the same direction (clockwise or counterclockwise) relative to the sun. After reading your post, it took very little analysis for me to realize that my concept on this issue was dead wrong.

I suppose that a not bad definition of a satellite orbit would be that a satellite reverses direction relative to its planet’s orbital path (Id est: An orbital path with “loops”).

I suppose it is possible for a satellite to have an orbital path with cusps, which seems strange. This would be the critical case between a satellite orbit and a perturbed planetary orbit.

I think this is the 3rd (maybe 4th or 5th?) time I have admitted being wrong in some Thread at this site. Might this be a record?
 
Dinosaur said:
Janus58: Thanx for correcting me. Your analysis seems valid.

I was surprised by your diagram of Callistro’s orbit. I thought that Luna was the only satellite in the solar system which does not have “loops” in its orbital path.

At one time, I briefly thought the same thing, until I actually analysed the orbital paths.
 
Billy T said:
to Janus58:



Certainly yours is the easiest to apply, but I prefer mine as with it the moon is not both a satellite and a planet as it is with yours.
Huh? How does adding a minumum size requirement make the Moon both a satellite and planet? All it does is remove objects below a certain size from the designation of planet.

Thanks for the answer to my second of two questions, but that leads me to ask: How did Earth capture the spent rocket in a two body inter action? ( I am assuming from your statement “It had been in Solar orbit until it recently was recaptured by the Earth“ that it was for some period not bound to the Earth. I.e. how did it get bound with negative potential again?) Perhaps it is not again bound to the earth - that could be the case if it is at one of the two stable Earth/sun Lagrange points, but if it is there Jupiter will surely set it free soon as those points are not very deep "holes."

It is believed that it was a encounter with the L1 point that caused the capture.
 
Janus58 said:
...How does adding a minumum size requirement make the Moon both a satellite and planet? ...
It does not. It was late and I was not expressing my idea/ concern well. Of course, the moon is not both satellite and planet (either by my definition distinuishing them: "Planets are always concave to sun", etc. or by yours: "If sun's gravity is stronger than that of near by body, it is a planet" Both definitions make the moon a planet.)

My dislike for your definition of a "satellite" MAY continue because I was not entirely happy with your answer to my first question. You said in answer: at more than 260,000km, the satellite becomes a planet. (This form is "Earth bound", not general, so I corrected that in my restatement of your definition above, as clearly that is your intent.)

If an objects "circling" Earth at 259,000km has parts of its solar orbit convex, I have no problem accepting your more simple (to apply) definition, for the Earth at least, but if this "259 satellite" (satellite by your definiton) always has only concave curvature in the solar orbit, then it would be a planet by my definition. Thus to accept to accept your definition distinguishing satellite from planet, I would need to abandon my definition that distinguish satellite from planet. It is not just "pride of ownership", (especially since my definition is built entirely on information you surprised me with) that makes me defend my definition. Let me try to state why I MAY object to your definition more accurately (at least without the erroneous "It makes moon both planet and satellite" statement):

I distinguish "planet" from "satellite" by the curvature of their solar orbits. You by the balance point of solar and near by body gravity. I am almost sure that by your definiton the "261 planet" or "barely a planet" planet of Earth could be a satellite of Neptune even if it were slightly more distant from Neptune than from Earth (Neptune's "265 satellite"). (Solar gravity at Neptune is much less and Neptune is much bigger than Earth so Neptune's 265 is surely a satellite by your definition.) It probably is still a satellite by my definition also as Neptune is progressing more slowly (angular rate) around the sun than Earth. But, are your sure that the more distant "just barely a Neptune satellite" (by your definition) does not have only concave curvature to sun, which would make it a planet by my definition? If it does have any convex part, then by my definition it is a satelite also. Certainly if the most distant satellite of Neptune were circling Earth at that distant, your definition would convert it from satellite to planet, but mine might not.
I suspect that even if mine also converts that most distant Neptune satellite into a planet, there may be some satellite of Nepturn that you definition converts to a planet if moved to orbit Earth at same separation, but my definition may lets it remain a satellite of Earth also.
I also suspect that some satellite of Neptune or some "extra massive Neptune" (your definition of satellite) could, at the same separation from Earth, just be a planet (your definition of satellite and planet). for example Earth's "planet 261" is surely Neptune's "satellite 261" It might still be a Neptune satellite by my definition also, i.e. exhibiting some convex curvature wrt the sun.
Very hard to express my concern with your definition clearly. No wonder I failed last night. Not sure I have it correct, and clear yet. Hope you see my concern. I want the definition to keep satellite a satellite of the larger body no mater how distant from the sun the "larger body" is, if the separation of satellite from "larger body" is held constant. I am not sure whose defition does this better. Perhaps both fail this test, but I strongly think yours fails.

What do you think? Is not my (stolen from you) definition better than yours?

Now a new point/ question. (It seem the more I learn from you, the more questions I have to ask you.)

You have shown that more than 2/3 of the gravity acting on moon comes from the sun (If one ignores fact gravity on moon is a single gravity field, not two separate ones.) That makes me realize that when the moon is on far side of Earth from sun it has roughly 3 units of gravity but only 1 unit of gravity when on the near sun side. Consequently moon's orbit must be far from any ellipse - Like most others here, prior to your post, I assumed (without thought) that Earth's gravity was very dominate, even that the sun's could be neglected!)

New question:

Can you describe, mathematically, the idealized shape of the moon's orbit as a funtion of its Earth/ sun gravity ratio? (the "1 to 2" or some other such characterization like 2/3 etc.) I suspect not, as the "three body problem" has no analytic solution, but perhaps you know a reasonable simple mathematical discription that is approximately correct?

Reason I ask is I am looking for "eggoid equations." If you have never looked at my threads "Jell-0 ..." OR "Co- authors wanted ...." please do so. I think all of the "gravity is a cosmic flux, not intrinsic to matter" concepts can be demolished by the "virtual work" / math approach outlined there. The "co- authors..." thread is a half finished draft of a paper that may be sent to a math/physic journal. It mainly lacks a few 3D integrations still. Perhaps you would become a co-author? I.e. do some of these integrations.


PS your "L1" answer to another question was both satisfying and interesting. Interesting because the common knowledge that capture is impossible without a "third body" is not exactly accurate. A "virtual third body" formed by two others will do.
 
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I want to appoligize to Dinosaur for helping steal / steer his thread far fom topic, but doubt if he minds as both he and I have learnd a lot form Janus58. Also it was Dinosaur who first took us on this lunar turn - I.e., it is all his fault :D
Perhaps we can return to topic now. To help this, I again post some earlier coments of mine:

I did not understand Ophiolite’s point about plate tectonics cycles encouraging advanced life forms nor why he asserts that: “inward migration of gas giants is a commonplace occurrence” Perhaps he will explain more fully.
I note that which way they are migrating is not an empirical fact. Only “large planets” that are relatively near their sun can be discovered by current techniques Thus fact the known ones are both relative closer to their sun than Jupiter and larger than Jupiter can not be taken as evidence for this migration.
The moon is migrating AWAY from the Earth because of tidal interactions, but this fact may not be a strong counter argument against the Ophiolite’s “towards star migration” as it simplistically appears to be, because I think that under certain conditions, which I can no longer recall, the lesser body can even escape from the greater by tidal interactions, although it may take infinite amount of time to do so as these interact rapidly weaken as the separation increases.
 
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Billy T said:
It does not. It was late and I was not expressing my idea/ concern well. Of course, the moon is not both satellite and planet (either by my definition distinuishing them: "Planets are always concave to sun", etc. or by yours: "If sun's gravity is stronger than that of near by body, it is a planet" Both definitions make the moon a planet.)

My dislike for your definition of a "satellite" MAY continue because I was not entirely happy with your answer to my first question. You said in answer: at more than 260,000km, the satellite becomes a planet. (This form is "Earth bound", not general, so I corrected that in my restatement of your definition above, as clearly that is your intent.)

If an objects "circling" Earth at 259,000km has parts of its solar orbit convex, I have no problem accepting your more simple (to apply) definition, for the Earth at least, but if this "259 satellite" (satellite by your definiton) always has only concave curvature in the solar orbit, then it would be a planet by my definition. Thus to accept to accept your definition distinguishing satellite from planet, I would need to abandon my definition that distinguish satellite from planet. It is not just "pride of ownership", (especially since my definition is built entirely on information you surprised me with) that makes me defend my definition. Let me try to state why I MAY object to your definition more accurately (at least without the erroneous "It makes moon both planet and satellite" statement):

I distinguish "planet" from "satellite" by the curvature of their solar orbits. You by the balance point of solar and near by body gravity. I am almost sure that by your definiton the "261 planet" or "barely a planet" planet of Earth could be a satellite of Neptune even if it were slightly more distant from Neptune than from Earth (Neptune's "265 satellite"). (Solar gravity at Neptune is much less and Neptune is much bigger than Earth so Neptune's 265 is surely a satellite by your definition.) It probably is still a satellite by my definition also as Neptune is progressing more slowly (angular rate) around the sun than Earth. But, are your sure that the more distant "just barely a Neptune satellite" (by your definition) does not have only concave curvature to sun, which would make it a planet by my definition? If it does have any convex part, then by my definition it is a satelite also. Certainly if the most distant satellite of Neptune were circling Earth at that distant, your definition would convert it from satellite to planet, but mine might not.
I suspect that even if mine also converts that most distant Neptune satellite into a planet, there may be some satellite of Nepturn that you definition converts to a planet if moved to orbit Earth at same separation, but my definition may lets it remain a satellite of Earth also.
I also suspect that some satellite of Neptune or some "extra massive Neptune" (your definition of satellite) could, at the same separation from Earth, just be a planet (your definition of satellite and planet). for example Earth's "planet 261" is surely Neptune's "satellite 261" It might still be a Neptune satellite by my definition also, i.e. exhibiting some convex curvature wrt the sun.
Very hard to express my concern with your definition clearly. No wonder I failed last night. Not sure I have it correct, and clear yet. Hope you see my concern. I want the definition to keep satellite a satellite of the larger body no mater how distant from the sun the "larger body" is, if the separation of satellite from "larger body" is held constant. I am not sure whose defition does this better. Perhaps both fail this test, but I strongly think yours fails.

What do you think? Is not my (stolen from you) definition better than yours?
First off, I have not given any actual definition for what I would consider a Planet. While the relative strengths of the gravitational attraction to the Sun and another body might be one factor to consider, There are other things to consider.(BTW, the distance at which these two equal each other is the boundary between completely concave heliocentric path or not. Also, the 260,000km figure is only for the Earth; Each ppanet would have its own boundary point.)

For example, if you had Earth mass bodies of equal (or even near equal size), that were separated by 160,000km, and thus neither followed a completely concave orbital path around the Sun, I would find it difficult not to still classify them both as planets.

Conversely, I would not classify a 2 kiloton rock co-orbiting with the Earth at a distance of 400,000 km as a planet. (otherwise every piece of rock orbiting the Sun in an independent Solar orbit would have to be considered a planet.) So you must have a lower mass cutoff for classification of Planet.

Obviously, size is a large factor. But not just size alone either. Ganymede is large enough that if it were in a solar orbit it would probably been called a planet, but it orbits Jupiter so it is a moon. This seems only right as it is so small compared to Jupiter. Thus with paired systems we should consider the mass ratio of the pair.

Thus I might consider a staring point for the definition of Planet:

1.A body of a certain minimum mass.
2.Which
a. Either orbits the Sun in an idependent orbit
Or
b. Co-orbits the Sun with another body at a distance greater than that at which the gravitational attraction between it and the Sun equals that between it and the other body.
or
c.Co-orbits the Sun with another body at a distance less than that at which the gravitational attraction between it and the Sun equals that between it and the other body and has a mass of at least 1/100 of the other body while still being greater than the minumum mass of rule one.

(1) Allows us to elliminate asteroids and Such.
(2a) Covers the conventional planets
(2b) Allows for bodies that meet (1) but are loosely gravitationally bound to another body (Ganymede would fit this rule if it were moved out to beyond Sinope.
(2c) Allow for Double planets such as I mentioned above, but still keeps the The large Jupiter moons as satellites of Jupiter. (this ratio is just a suggestion, and could be fine tuned.)

Now a new point/ question. (It seem the more I learn from you, the more questions I have to ask you.)

You have shown that more than 2/3 of the gravity acting on moon comes from the sun (If one ignores fact gravity on moon is a single gravity field, not two separate ones.) That makes me realize that when the moon is on far side of Earth from sun it has roughly 3 units of gravity but only 1 unit of gravity when on the near sun side. Consequently moon's orbit must be far from any ellipse - Like most others here, prior to your post, I assumed (without thought) that Earth's gravity was very dominate, even that the sun's could be neglected!)
Remember, the Sun acts on the Earth too, so you have to take the differential across the Earth-moon system to get any net force pulling on the Moon's orbit. (in effect, since the 2 units of graivty act on both the earth and moon, it pretty much drops out when considering the Earth-moon system alone). The moon is slightly closer to the sun when it is on the near sun side than it is on the far side, and this does cause a small tidal effect across the orbit. As a result, the moon's orbit is stretched a little bit along the line joining the Earth and Sun. This has the effect of increasing the eccentricity of the Moon's Earth orbit slightly when the major axis aligns with the Earth and Sun and the effect of decreasing the eccentricity when the minor axis does.
 
Dinosaur said:
A recent anthology of Scientific American reprints included an article from the October 2001 issue, which discussed the GHZ (Galactic Habitable Zone) suitable for the development of life. The article concludes that complex life forms are rare in our galaxy.

A solar system too close to the center of the galaxy is not likely to harbor any complex life forms due to orbital instabilities (caused by rapidly moving stars), too much radiation (due to massive stars & activity of the central black hole), and cometary/asteroid impacts (due to more objects in the Oort Cloud & Kuiper belt, as well as more disturbances of those regions caused by nearby stars).

A solar system too far from the galactic center will not have sufficient heavy elements, which are necessary to living organisms. Elements other than hydrogen and helium are created by stars which go nova at the end of their life cycles. In particular, type II novae are required for the creation of many of the heavier elements. In the outer fringe of the galaxy, there have not been enough nova events to create the abundance of heavy elements required by life forms.

The above considerations limit the GHZ to a narrow ring centered near the position of the solar system (about 28,000 light years from galactic center).

Our solar system happens to be in a unique zone of the galaxy. The orbital rotation rate of our solar system around the galactic center closely matches the rotation rate of the galaxy. This results in our staying away from the center of the spiral arms for billions of years. This might be a necessary condition for the development of complex life forms. Near the center of the spiral arms the density of stars is higher, making disturbances of the Oort Cloud and Kuiper belt objects more likely. There is also increased likelihood of possible orbital instabilities due to stars passing even closer than the distance resulting in Oort Cloud disturbances.

If being in this special zone is a requirement for the development of complex life forms, the GHZ is very narrow. Note that it took about one billion years for simple life to occur on the Earth and another 2 billion or so years for complex life forms to evolve. It could be that staying away from the spiral arms for 3 billion or so years is required for the development of complex life forms.

There is another interesting consideration mentioned by the SciAm article. The required abundance of heavy elements in the GHZ in conjunction with a less dangerous environment less did not occur until about 5 billion years ago, about the time of the start of the gravitational collapse of the dust cloud which formed our solar system.

The size of the GHZ restricts the development of complex life forms to a particular region of space. The history of the creation of heavy elements and the lessening of catastrophic events restricts the development of complex life forms to recent times.

All of the above strongly suggests that we might be the first intelligent life form in our galaxy, and possibly the only one.

The SciAm article also mentioned the Fermi Paradox. A space traveling ET searching for habitable planets and/or other technological civilizations would not roam the galaxy randomly. They would search the GHZ. Since we have no evidence that they have noticed us, we can surmise that they do not exist, or they are not searching, or they have not been searching for a long time.

I happen to have the issue of October 2001, and in it, I read that the author of the article, Guillermo Gonzalez, was also the person that proposed the concept of GHZ, concretely in 1999, so maybe he can be a bit biased in his conclusions, as 2inquisitive noted. I don't think that we are the only intelligent civilization of the Galaxy, I bet that there are 2 or 3 more at least
 
Janus58 said:
....BTW, the distance at which these two equal each other is the boundary between completely concave heliocentric path or not....
Thanks. Glad to see there is no difference between "my definition" (really one stolen from your superior knowledge in these matters) and the excessively simple one I put in your mouth. All your points are well taken. Thanks for putting up with me. I too am patient with some one ignorgant, but obviously trying to learn, however, If I were you and and you were me, I think by now I would have at least become irritated enough to complain or make a few jokes at your expense. Thanks a again. - I have learned a lot from you. I think we can let the thread return to topic now, as I suggested in recent post.
 
Seems like we're thinking inside the box. We're assuming that all life has to be like life here. DNA, or at least carbon-based organic molecules and water. Maybe silicon-based if we really stretch the envelope.

Sci fi writers with plenty of credentials in real science have been postulating other types of life for decades.
 
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