Why are Planets in the Same Plane?

kferris61 · Feb 28, 2006

Any diagrams, that I have seen, of our solar system show all the planets being in the same plane. Is this how it really is or is this a simplification?

mkofron · Feb 28, 2006

http://www.physlink.com/Education/AskExperts/ae588.cfm

Saiph · Feb 28, 2006

not a simplification...or much of one. The planets are all on the same plane, give or take only a few degree tilt. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

CalliArcale · Feb 28, 2006

The major planets are very close to being in the same plane (called the "plane of the ecliptic"), with the exception of Pluto, although of course there is debate about whether or not it counts. <img src="/images/icons/wink.gif" /> Most of the "main belt" asteroids also orbit near the plane of the ecliptic. Smaller bodies tend to be more erratic than the big ones, and things also seem to get much more erratic in the far reaches of the solar system. This may be due to the declining influence of the Sun's gravity as you move out, or declining influence of early rotation in the protoplanetary nebula from which the solar system formed. Or it may simply be an observer bias; it may be easier to spot things out of the plane of the ecliptic in the outer solar system because their relative motion seems so dramatic. However, Mercury is notably inclined as well. The ecliptic is the imaginary line in the sky formed by the Sun's path over the course of the year. It is also the Earth's orbit. The plane of the ecliptic is the plane described by this orbit. The orbital inclination of each of the planets is expressed in terms of the angle it forms with the plane of the ecliptic. Cribbed from The Nine Planets, Appendix 1a, here are the orbital inclinations of the major planets expressed in degrees (including Pluto). For fun, I've also included their orbital eccentricity. Eccentricity is a ratio of the distance between the foci of an ellipse and its major axis; bigger numbers are flatter ellipses and zero is a true circle. Object Incl Eccen Mercury 7.00 0.21 Venus 3.39 0.01 Earth 0.00 0.02 Mars 1.85 0.09 Jupiter 1.31 0.05 Saturn 2.49 0.06 Uranus 0.77 0.05 Neptune 1.77 0.01 Pluto 17.15 0.25 <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

mikeemmert · Feb 28, 2006

I think of equal interest is something called the invariable plane. The plane of the ecliptic has to do with the plane of the Earth's orbit around the sun. Since most telescopes are on earth, the ecliptic plane is very important for aiming them. But the Earth is only one planet, and one of the smaller ones. Should Earth define the plane of the Solar System? From wikipedia: "The invariable plane of the solar system is the plane passing through its barycenter (center of mass) which is perpendicular to its angular momentum vector, about 98% of which is contributed by the orbital angular momenta of the four jovian planets (Jupiter, Saturn, Uranus, and Neptune). It is also called the Laplacian plane after the French astronomer who first recognized it, Pierre Simon Laplace. The invariable plane is within 0.5° of the orbital plane of Jupiter, and may be regarded as the weighted average of all planetary orbital planes. The magnitude of the orbital angular momentum vector of a planet is L = RMV, where R is the orbital radius of the planet (from the barycenter), M is the mass of the planet, and V is its orbital velocity. That of Jupiter contributes the bulk of the solar system's angular momentum, 60.3%. Then come Saturn at 24.5%, Neptune at 7.9%, and Uranus at 5.3%. The Sun forms a counterbalance to all of the planets, so the barycenter moves from the center of the Sun when Jupiter is on one side and the other three jovian planets are diametrically opposite on the other side of the Sun, to 2.17 solar radii away from the center of the Sun when all are in line on one side (admittedly unlikely). The orbital angular momenta of the Sun and all non-jovian planets, moons, and minor solar system bodies, as well as the axial rotation momenta of all bodies, including the Sun, total only about 2%. If all solar system bodies were point masses, or were rigid bodies

mubashirmansoor · Feb 28, 2006

Because all the planets in our solar system except pluto are from the same nebula (cloud) and that made them to be in the same plane. Pluto is from another one.

CalliArcale · Mar 1, 2006

That is possible, but seems unlikely to me. There are an awful lot of KBOs and other objects in the far reaches of the solar system in inclined orbits -- sometimes much more highly inclined than Pluto's. Perhaps a few are captured objects, but it seems to me that we wouldn't see as many objects inclined to the plane of the ecliptic if this only happened due to gravitational capture. My guess is that there is a trend as you get further out; perhaps early rotation in the protoplanetary nebula puts a bias on a forming object's orbit, and this bias becomes progressively less significant the further out you get. That's my hunch right now, but I don't really have the scientific background to explore it further. Gravitational interactions are also sometimes blamed; after all, there are definite known cases of objects changing orbital inclination due to interactions with more massive planets. Some have speculated that Pluto and Triton may have shared a common past. Triton orbits retrograde (backwards -- against planetary rotation) around Neptune, which is highly unstable and clear evidence that it has not always been in that orbit. Most likely, it was gravitationally captured by Neptune. And Pluto is in an orbital resonance with Neptune (2:3 if memory serves; for every three Neptune "years", Pluto has two "years"). Could a gravitational interaction with Neptune have shoved Pluto away from the ecliptic? Perhaps, but of course that doesn't explain things like Sedna, which is much too far away for that explanation. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

CalliArcale · Mar 1, 2006

<blockquote>In reply to:<hr />The plane of the ecliptic has to do with the plane of the Earth's orbit around the sun. Since most telescopes are on earth, the ecliptic plane is very important for aiming them. But the Earth is only one planet, and one of the smaller ones. Should Earth define the plane of the Solar System?<hr /></blockquote> The plane of the ecliptic for the solar system is a special case. The ecliptic has been defined since ancient times, since before they realized Earth might not orbit in the same plane as the Sun's equator. (Indeed, there were times when such a suggestion might get you killed, as it would indicate an aesthetically imperfect solar system.) So for historical reasons, this plane is still used even though it has an obvious geocentric bias and isn't all that meaningful in terms of celestial mechanics. For every other body, the plane of the ecliptic (used for describing the orbits of the body's satellites) is defined by its equator, which in turn is defined as being exactly perpendicular to the body's rotational axis. For instance, the ISS orbits at an inclination of 51 degrees. This is measured against the plane of the Earth's equator. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

harmonicaman · Mar 1, 2006

"Because all the planets in our solar system except pluto are from the same nebula (cloud) and that made them to be in the same plane. Pluto is from another one." I don't think there is any compelling evidence that the origin of Pluto is somehow different than the other planets or KBOs.

llivinglarge · Mar 1, 2006

According to the nebular theory... Our solar system was created by the flattening of a spinning stellar cloud.

chriscdc · Mar 2, 2006

Do you know whether the plane of the solar system is the same as the galactic plane?

CalliArcale · Mar 2, 2006

It is not the same plane. I don't recall exactly how far the ecliptic is inclined to the plane of the galaxy, but it's gotta be quite a lot. Viewers in the Northern Hemisphere are treated to glorious nighttime views of the Milky Way, especially in the summer when it is quite high in the sky. Actually, the vast majority of stars you see are in the Milky Way; the dense band of stars known since ancient times as the Milky Way is in fact the galactic center. Southern hemisphere viewers do not see this as well. However, they are treated to something completely different: the spectacular Magellanic Clouds. These are small, irregular satellite galaxies of our own Milky Way Galaxy and they dominate the southern skies. If you think about the geometry of this (that northern viewers get the best views of the inside of the galaxy, and southern viewers get the best views of the outside of the galaxy), that should provide something of an answer. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

mubashirmansoor · Mar 3, 2006

So is there any diffrence between comolus and stratus in nature but still diffrently recognised and cant get together

CalliArcale · Mar 3, 2006

The protoplanetary nebula has nothing to do with the kinds of clouds you get on Earth (such as cumulus and stratus). The protoplanetary nebula held together under its own gravity; clouds on Earth don't hold together nearly as well, staying together only as long as atmospheric conditions permit. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

mubashirmansoor · Mar 3, 2006

But don't you think that our solar system's planets had been from one nebula and pluto part of the kyperbelt? which had the ability to escape because of certain gravitational causes?

mubashirmansoor · Mar 3, 2006

Couldn't that other nebula be somehow the same as ours? And in general isn't the mater all over the universe the same? because its all from the point of singularity=the same combination all over the universe?

mubashirmansoor · Mar 3, 2006

You are 100% correct, this was what I read in the book "wonders of universe" written by prof. Victory

nexium · Mar 4, 2006

So none of the planets are in the same plane, but most are within a few degrees.

CalliArcale · Mar 8, 2006

<blockquote>In reply to:<hr />But don't you think that our solar system's planets had been from one nebula and pluto part of the kyperbelt? which had the ability to escape because of certain gravitational causes?<hr /></blockquote> It seems much more probable to me that the major planets and the Kuiper Belt formed from the same nebula. A few might've been captured from a passing system, perhaps, but I would think they'd have a strong skew in their distribution if the majority of them were captured; I wouldn't think such interactions between solar systems would happen particularly often, after all. But of course that doesn't mean it's impossible. Your notion is indeed quite plausible. I just don't think it's what happened, because it seems much less likely to me. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

llivinglarge · Mar 8, 2006

Mercury's orbit is slightly tilted.

CalliArcale · Mar 9, 2006

Yep. That's the biggest problem to my hunch that maybe there's less bias towards equatorial orbits as you move away from the Sun. Then again, maybe Mercury's just an exception. It is an odd little world. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

Why are Planets in the Same Plane?

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