If you're a Phd who has spent your whole life researching and proving something then you're likely to opposed someone proving eactly the opposite. This is true to some extent, but it glosses over another even more important point: most newly proposed theories are wrong. (It's a lot like mutations in evolutionary biology.) Many of the theories are still-born, never making it past someone's blackboard before they're shot down, but quite a few get floated. Some get floated quite adamantly by their adherents. A few are better than the older models. After even a little while in science, you see the ratio and it's natural to want to stick to the tested theory until the new guy has been able to provide some strong evidence for itself.
That's sort of the rub, though, isn't it? Only a few new theories which suplant the old model do so with a really compelling single test. We can think of a few of the exceptions: General Relativity and the 1919 eclipse, the Big Bang (which was already pretty widely accepted, but never mind) and the discovery of the CMB, the giant impact theory of the origin of the Moon and the numerical simulations of the 1980s, etc. But these *are* the exceptions. Most theories which will eventually take over do so by slow accumulation of evidence in their favor, not with any slam dunk. As a result, convincing scientists to abondon the older model is difficult and there's no magic cut-off where you can say, "Now the new theory is better than the old one." So are the scientists being bad at science? Sure, it's easy to spin the narrative that way, but I'd say no. They're at worst being conservative and not wanting to leap onto a new model until they see that it's really better.
Anyone expecting unbiassed science to come out of that lot is just a misguided idealist. Now I feel like you're being insulting. Individual scientists are human, we have our flaws and our blind-spots. Some of us have real agendas and a few are even downright dishonest. But as a group, we're contradictory, curious, and anti-authority. As a result, science is pretty good at self-correcting. A single scientist can lie to himself or even lie to others. But that always gets caught eventually because someone starts asking questions and we collectively have no vested interest in covering up lies.
(Any time you hear about scientists being involved in a massive conspiracy, like some anti-global warming fanatics will try to tell you, you can bet it's wrong. Any person who could prove evolution or GW conclusively incorrect would have just made a career and world-wide fame for herself.)
This is quite logical, as it's human nature to do so, and not a direct result of one's career field. You're absolutely correct. Think of all the stories of some technological innovation you've heard that follow this same pattern. ("Everyone believed that building a kerbudle with transducing fleebs was impossible, but one lonely inventor decided to try it. [Story continues, ignoring that the inventor was paid to do the investigation, however long a shot it was deemed, by some well-known company, etc.]") Or even business: "Everyone said that Microsoft's/Apple's/Intel's/etc's hold on X market was unassailable, but this plucky [they're always plucky] little start-up set out to fight the Goliath." It's human nature and it's good story-telling, which is what sells science articles.
Question is, is there another way to tell the stories that isn't so formulaic and that doesn't give such an incorrect impression?
But it does matter. If the plane is 1,000 light years thick, then anything within that field, like a ring at 45 degrees to the plane, would remain at that angle as the attraction on all particles would be the same as the whole ring as it is blanketed by the same force vector. I just agree that that was true, and then clearly stated that if the galaxy were NOT thick disk, something slightly different would happen. (That's the "Even if" part.) Why are you disagreeing and then repeating what I just said was true?
However anything above the plane and (eg) about 75,000 light years out, would travel on a ballistic curve toward the center. You're confusing two things: stars that oscillate above and below the galactic mid-plane (which they do... they don't get pulled into a monolayer as you seem to be suggesting) and solar systems, which is what we *were* talking about. A solar system orbits its star first and foremost. The extra forces of the galaxy, which are very small compared to the effects of the star, would have a minor effect. If the star is *in* the midplane but the planets were to orbit so that they passed above and below it (see: monolayer galaxy), the vertical frequency of the orbits would change but not the plane of the orbit. Look it up in any book on ring physics: the effect of the non-spherical distribution of mass is to alter the various frequencies (vertical, epicyclic, mean motion), but not the inclination.
If the star is OUT of the galactic midplane, you still don't get a change in the inclination, although you do shift the location of the orbit (if memory serves).
It would be interesting statistical physics to find out how many systems' plane is aligned to the galactic plane or at azimuth (90 degrees). Been done, they're randomly oriented. Random motions in the gas clouds that collapse to form stars and planets overwelm the effects of the galaxy and the galaxy simply doesn't torque the planes into its own.
That's also very important, but it wasn't what I was talking about. Even if the galactic plane were thinner than the solar system's scale, it wouldn't matter. The forces would be symmetrical on either side of the plane crossing. (Not that galactic forces are even significant in the parts of the solar system that are coplanar anyway.)
True (I thought about pointing out that Saturn's moons are all named for Titans, characters associated with Titans, or Titan-like gods* myself), but I think the fact that it's Rhea that has the (possible) ring is still an amusing coincidence.
* Except the shepherds Pan and Daphnis, of course. Who are named for, um, shepherds.
Actually, you'd probably be better not making the force radial by trying to kill some angular momentum instead. Assuming you *want* to smash the Moon into the Earth.
Er, not really. For the most part, the galactic disk's effects would only be to make the planets move "up and down" (relative to the galactic plane) somewhat faster than you'd expect for an isolated system. It does not pull them into the same plane. Why? Because the z-directed forces on both sides of galactic-plane crossing are symmetrical.
If your statement were true, Saturn's rings would probably be in the ecliptic plane by now. They're a much older system, dynamically-speaking, than the solar system (let alone the galaxy).
Saturn's rings are in the equatorial plane of Saturn to within any margin of error we've been able to come up with. (I actually needed to confirm that this was true to some insanely precise level, like 0.001 degrees or something, just a little while ago for research purposes.)
But its mostly older galaxies without much dust, plasma, and debris that take such form. In other words, elliptical (roundish) galaxies have little or no friction or collisions among stars. The stars don't interact very often (with each other or with diminishing plasma and dust). The fact that most elliptical galaxies are "cleaner" than spirals is evidence for this.
Also, the average width of the particles in Saturn's rings in proportion to the space between them is much much larger than the ratio of the star sizes to their separation in older galaxies. Models suggest that ring particles can and do collide often. This was exactly my point.
That's because the collapsing solar disk's average momentum may have been shaped by forces stronger than the galaxy's movement, such as a nearby supernova explosion soon before collapse of the solar disk. Such explosions are often oblique or bipolar in shape, meaning they may press on one side of a plasma cloud more than another. Plus, there's lots of nearby stars in formation clusters giving unpredictable gravity kicks. Also true, and also my point.:-)
Inclination of the orbit has nothing to do with the total angular moment. h = sqrt(G M a (1-e^2)), where h is the specific angular moment, G is Newton's constant, a is the semi-major axis of the orbit, M is the central body's mass (I'm assuming a point source), and e is the eccentricity. Note the lack of the inclination in there. If you think about it, it *has* to be ascent: unlike e and a, the reference plane (and therefore I) is really arbitrary. There are often better choices than others, but they're in no way absolute.
The existence (especially the high frequency of) elliptical and irregular galaxies supports this idea that disks aren't inherently required, even if they are very common.
Our solar system's flatness and the rings or Saturn is also entirely unrelated to the galaxy's shape. If it where related, you'd expect the solar system's plane to be the same as the galaxy (it isn't: prove it to yourself and look at the line of the planets in the night sky and compare it to the line that the galaxy makes). Likewise, Saturn's rings are tilted relative to the ecliptic plane by 26 degrees so that they line in Saturn's equatorial plane.
Why are things flat? Collisions. Collisions average out velocities so they tend to a single plane. (How flat you get depends on collision frequency and any pressure support.)
It's not how the math works out, it's collisions. When inelastic bodies collide, their post-collision velocities tend to be nearer the (mass-weighted) average of the original velocities. For bodies orbiting a planet, the average motion is generally in the equatorial plane. Thus, for rings (or gas disks around a variety of astronomical bodies), you get flattened features. Saturn's main rings (C, B, and A) are so optically think (think "dense" if you will) that they're very, very flat. Measurements suggest that the B and A rings may be as little as a few meters thick because of all the collisions.
I know of no moon with rings, but I may be missing an old press-release somewhere.:-)
If the central body is spherical symmetrical, its rotation is entirely irrelevant. If it has any asymmetry, things get more interesting. A lone satellite (or satellites that don't interact significantly) will have their orbits precess in space, but they won't tend toward the equator. However, if you have interacting satellites, all sorts of things can happen. In the case of rings/disks, collisions betweens bodies averages out their velocities/orbits, which usually puts them in the planet's equatorial plane.
Depending on your definition of "in the rings", there are around 5 moons (shepherds all) already known: Pan (Encke gap), Daphnis (Keeler gap), Atlas (Roche gap), and Prometheus and Pandora (shepherding the F ring). However, I'd be careful calling this the outer rings: the E and G rings are exterior to the F ring.:-)
Despite JPL's press-release filled with certainty, this is not a definite detection. The imaging instrument has not seen any ring or halo around Rhea in spite having looked. This does not prove that the putative ring is not there (more observations are planned), but it is contrary evidence and suggests we start asking ourselves what else might cause these data.
Cassini, NASA's largest solar system mission ever, has around 5 Gb on its solid state recorder. (That's right, giga-*bits*.) Of course, with downlink rates being as slow as they are, it may be for the best. (Mars would have a much higher data rate to Earth for the same size antennae, naturally.)
Actually, I think that the Pioneer anomaly runs the other way. In any case, the Anderson et al. mega-paper tried to factor in pretty much every effect that they could concoct, include solar radiation, thermal radiation from the spacecraft, etc. It was an impressive bit of work to reach the conclusion, "still scratching our heads." (Not to belittle it. There's considerable value in papers that say, "This doesn't work," although this fact is often overlooked in science.)
I can't speak to this specific case, but someone did a study several years ago of the Voyager anomaly and whether it could be a gravitational effect. The gist of the analysis was the if it were gravitational, it would also affect the distribution of long-period comets, especially the "new" ones from the Oort cloud. They calculated the effect you'd expect and it's much too large relative to what we see in the comets, so whatever is affecting Voyager pretty much cannot be gravitational in nature.
It's also worth noting that even in the mega-analysis by Anderson et al. concluded that although they couldn't determine a source for the anomaly, they still generally felt that it was more likely to be endogenic than exogenic.
I can actually address this with some knowledge as I did a journal club a few years ago (when I was still in grad school) on a paper addressing this very topic.
It's long been suspected that this would happen. Certainly everyone who studied the topic much was confident that Mercury and Venus were toast and, say, Jupiter was OK. Earth has been dodgy to predict, though, it's right on the boundary of where the Sun will expand to during the red giant phase. Throw in the effects of changing dynamics (mass loss from the Sun, torques on Earth, etc.) leading to orbit changes, it all came down to the precise model you used for stellar evolution. As I recall, the paper I looked at about 3-5 years ago examined 10 models and found somewhere around half (60% seems to ring a bell) lead to Earth's obliteration.
So although astronomy shows may have presented it as known fact in the early 1980s (certainty sells and destroying Earth is sexy), it really wasn't.
just round up a bunch of people, put them on airplane-shaped spaceships, and then drop a bunch of H-bombs on them. It's just not very flexible as a philosophy.
Sure, but to give Xenu his due: I always seem to feel better after doing this, too. It's even more effective at picking me up than ice cream.
How long do you think it takes? Tidal breakup ought to occur on a timescale of orbits, meaning a few days. These bodies have persisted for at least decades and there is evidence that they formed with the rings which are at millions, if not billions, of years old. It sounds like you're grasping at straws to support an invalid claim. There are moons inside the Roche limit because they *can* exist there thanks to internal strength (a factor neglected in the Roche calculations). It's just *forming* moons there that's difficult.
Actually, the G ring is exterior to the E ring. The F ring's status is questionable in this respect (it depends on your assumptions). Even the outer A ring might be outside the Roche limit, depending on what physics you think is occurring.
Also, existing satellites don't break up inside to the Roche limit. Pan and Daphnis are most likely within this limit, yet persist. Atlas, Prometheus, Pandora, and maybe even Janus and Epimetheus are potentially inside the Roche limit, depending on your choice of assumptions.
The Roche limit, as usually defined, is for a body with *no* internal strength. This is a very reasonable limit to use as anything trying to accrete from small particles would not have internal strength (between these particles) immediately. It's difficult to invoke any kind of strong enough force to overcome the tidal stretching: electrostatic charges, for example, are too small to work on macroscopic bodies --- large charges don't persist for long as they attract opposite charges quickly and cancel out. (Besides, as soon as two opposite-charged ring particles meet, I suspect that they'd exchange charges faster than you can sinter the particles together. Once the charges are equalized, there's no more force to hold them together.) The only way of triggering growth in the main rings that I know of is to seed the growth with larger cores which are dense enough to attract the smaller ring particles and hold on to them for long enough for the ices to bond together. Of course, this process is self-limiting. (http://science.slashdot.org/article.pl?sid=07/12/07/1326240)
On the other hand, bodies *with* internal strength have a very different tidal limit. If the strength is similar to what we are used to on Earth, then there's no real reason to worry about Saturn right down to the planet's "surface". (Consider Earth: we're well inside the Roche limit, but satellites (and astronauts!) don't fall apart.)
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That's sort of the rub, though, isn't it? Only a few new theories which suplant the old model do so with a really compelling single test. We can think of a few of the exceptions: General Relativity and the 1919 eclipse, the Big Bang (which was already pretty widely accepted, but never mind) and the discovery of the CMB, the giant impact theory of the origin of the Moon and the numerical simulations of the 1980s, etc. But these *are* the exceptions. Most theories which will eventually take over do so by slow accumulation of evidence in their favor, not with any slam dunk. As a result, convincing scientists to abondon the older model is difficult and there's no magic cut-off where you can say, "Now the new theory is better than the old one." So are the scientists being bad at science? Sure, it's easy to spin the narrative that way, but I'd say no. They're at worst being conservative and not wanting to leap onto a new model until they see that it's really better. Anyone expecting unbiassed science to come out of that lot is just a misguided idealist. Now I feel like you're being insulting. Individual scientists are human, we have our flaws and our blind-spots. Some of us have real agendas and a few are even downright dishonest. But as a group, we're contradictory, curious, and anti-authority. As a result, science is pretty good at self-correcting. A single scientist can lie to himself or even lie to others. But that always gets caught eventually because someone starts asking questions and we collectively have no vested interest in covering up lies.
(Any time you hear about scientists being involved in a massive conspiracy, like some anti-global warming fanatics will try to tell you, you can bet it's wrong. Any person who could prove evolution or GW conclusively incorrect would have just made a career and world-wide fame for herself.)
Question is, is there another way to tell the stories that isn't so formulaic and that doesn't give such an incorrect impression?
If the star is OUT of the galactic midplane, you still don't get a change in the inclination, although you do shift the location of the orbit (if memory serves). It would be interesting statistical physics to find out how many systems' plane is aligned to the galactic plane or at azimuth (90 degrees). Been done, they're randomly oriented. Random motions in the gas clouds that collapse to form stars and planets overwelm the effects of the galaxy and the galaxy simply doesn't torque the planes into its own.
That's also very important, but it wasn't what I was talking about. Even if the galactic plane were thinner than the solar system's scale, it wouldn't matter. The forces would be symmetrical on either side of the plane crossing. (Not that galactic forces are even significant in the parts of the solar system that are coplanar anyway.)
True (I thought about pointing out that Saturn's moons are all named for Titans, characters associated with Titans, or Titan-like gods* myself), but I think the fact that it's Rhea that has the (possible) ring is still an amusing coincidence.
* Except the shepherds Pan and Daphnis, of course. Who are named for, um, shepherds.
Why is the L1 point special in this regard?
Actually, you'd probably be better not making the force radial by trying to kill some angular momentum instead. Assuming you *want* to smash the Moon into the Earth.
Er, not really. For the most part, the galactic disk's effects would only be to make the planets move "up and down" (relative to the galactic plane) somewhat faster than you'd expect for an isolated system. It does not pull them into the same plane. Why? Because the z-directed forces on both sides of galactic-plane crossing are symmetrical.
If your statement were true, Saturn's rings would probably be in the ecliptic plane by now. They're a much older system, dynamically-speaking, than the solar system (let alone the galaxy).
Saturn's rings are in the equatorial plane of Saturn to within any margin of error we've been able to come up with. (I actually needed to confirm that this was true to some insanely precise level, like 0.001 degrees or something, just a little while ago for research purposes.)
Also, the average width of the particles in Saturn's rings in proportion to the space between them is much much larger than the ratio of the star sizes to their separation in older galaxies. Models suggest that ring particles can and do collide often. This was exactly my point. That's because the collapsing solar disk's average momentum may have been shaped by forces stronger than the galaxy's movement, such as a nearby supernova explosion soon before collapse of the solar disk. Such explosions are often oblique or bipolar in shape, meaning they may press on one side of a plasma cloud more than another. Plus, there's lots of nearby stars in formation clusters giving unpredictable gravity kicks. Also true, and also my point.
I was going to suggest http://ciclops.org/search.php?x=0&y=0&search=rhea which has quite a few Rhea images. (Now with less Slashdotting!)
You nearly nailed it. :-D All you need to throw in there is how collisions average velocities/orbits and you'll be competing for my job. ;-)
Whoever told you this was wrong.
Inclination of the orbit has nothing to do with the total angular moment. h = sqrt(G M a (1-e^2)), where h is the specific angular moment, G is Newton's constant, a is the semi-major axis of the orbit, M is the central body's mass (I'm assuming a point source), and e is the eccentricity. Note the lack of the inclination in there. If you think about it, it *has* to be ascent: unlike e and a, the reference plane (and therefore I) is really arbitrary. There are often better choices than others, but they're in no way absolute.
The existence (especially the high frequency of) elliptical and irregular galaxies supports this idea that disks aren't inherently required, even if they are very common.
Our solar system's flatness and the rings or Saturn is also entirely unrelated to the galaxy's shape. If it where related, you'd expect the solar system's plane to be the same as the galaxy (it isn't: prove it to yourself and look at the line of the planets in the night sky and compare it to the line that the galaxy makes). Likewise, Saturn's rings are tilted relative to the ecliptic plane by 26 degrees so that they line in Saturn's equatorial plane.
Why are things flat? Collisions. Collisions average out velocities so they tend to a single plane. (How flat you get depends on collision frequency and any pressure support.)
It's not how the math works out, it's collisions. When inelastic bodies collide, their post-collision velocities tend to be nearer the (mass-weighted) average of the original velocities. For bodies orbiting a planet, the average motion is generally in the equatorial plane. Thus, for rings (or gas disks around a variety of astronomical bodies), you get flattened features. Saturn's main rings (C, B, and A) are so optically think (think "dense" if you will) that they're very, very flat. Measurements suggest that the B and A rings may be as little as a few meters thick because of all the collisions.
I know of no moon with rings, but I may be missing an old press-release somewhere. :-)
If the central body is spherical symmetrical, its rotation is entirely irrelevant. If it has any asymmetry, things get more interesting. A lone satellite (or satellites that don't interact significantly) will have their orbits precess in space, but they won't tend toward the equator. However, if you have interacting satellites, all sorts of things can happen. In the case of rings/disks, collisions betweens bodies averages out their velocities/orbits, which usually puts them in the planet's equatorial plane.
Depending on your definition of "in the rings", there are around 5 moons (shepherds all) already known: Pan (Encke gap), Daphnis (Keeler gap), Atlas (Roche gap), and Prometheus and Pandora (shepherding the F ring). However, I'd be careful calling this the outer rings: the E and G rings are exterior to the F ring. :-)
Despite JPL's press-release filled with certainty, this is not a definite detection. The imaging instrument has not seen any ring or halo around Rhea in spite having looked. This does not prove that the putative ring is not there (more observations are planned), but it is contrary evidence and suggests we start asking ourselves what else might cause these data.
Cassini, NASA's largest solar system mission ever, has around 5 Gb on its solid state recorder. (That's right, giga-*bits*.) Of course, with downlink rates being as slow as they are, it may be for the best. (Mars would have a much higher data rate to Earth for the same size antennae, naturally.)
Actually, I think that the Pioneer anomaly runs the other way. In any case, the Anderson et al. mega-paper tried to factor in pretty much every effect that they could concoct, include solar radiation, thermal radiation from the spacecraft, etc. It was an impressive bit of work to reach the conclusion, "still scratching our heads." (Not to belittle it. There's considerable value in papers that say, "This doesn't work," although this fact is often overlooked in science.)
Er, re-reading my post I just noticed that I should have said "Pioneer" rather than "Voyager". Apologies for any confusion.
I can't speak to this specific case, but someone did a study several years ago of the Voyager anomaly and whether it could be a gravitational effect. The gist of the analysis was the if it were gravitational, it would also affect the distribution of long-period comets, especially the "new" ones from the Oort cloud. They calculated the effect you'd expect and it's much too large relative to what we see in the comets, so whatever is affecting Voyager pretty much cannot be gravitational in nature.
It's also worth noting that even in the mega-analysis by Anderson et al. concluded that although they couldn't determine a source for the anomaly, they still generally felt that it was more likely to be endogenic than exogenic.
I can actually address this with some knowledge as I did a journal club a few years ago (when I was still in grad school) on a paper addressing this very topic.
It's long been suspected that this would happen. Certainly everyone who studied the topic much was confident that Mercury and Venus were toast and, say, Jupiter was OK. Earth has been dodgy to predict, though, it's right on the boundary of where the Sun will expand to during the red giant phase. Throw in the effects of changing dynamics (mass loss from the Sun, torques on Earth, etc.) leading to orbit changes, it all came down to the precise model you used for stellar evolution. As I recall, the paper I looked at about 3-5 years ago examined 10 models and found somewhere around half (60% seems to ring a bell) lead to Earth's obliteration.
So although astronomy shows may have presented it as known fact in the early 1980s (certainty sells and destroying Earth is sexy), it really wasn't.
Sure, but to give Xenu his due: I always seem to feel better after doing this, too. It's even more effective at picking me up than ice cream.
How long do you think it takes? Tidal breakup ought to occur on a timescale of orbits, meaning a few days. These bodies have persisted for at least decades and there is evidence that they formed with the rings which are at millions, if not billions, of years old. It sounds like you're grasping at straws to support an invalid claim. There are moons inside the Roche limit because they *can* exist there thanks to internal strength (a factor neglected in the Roche calculations). It's just *forming* moons there that's difficult.
Actually, the G ring is exterior to the E ring. The F ring's status is questionable in this respect (it depends on your assumptions). Even the outer A ring might be outside the Roche limit, depending on what physics you think is occurring.
Also, existing satellites don't break up inside to the Roche limit. Pan and Daphnis are most likely within this limit, yet persist. Atlas, Prometheus, Pandora, and maybe even Janus and Epimetheus are potentially inside the Roche limit, depending on your choice of assumptions.
The Roche limit, as usually defined, is for a body with *no* internal strength. This is a very reasonable limit to use as anything trying to accrete from small particles would not have internal strength (between these particles) immediately. It's difficult to invoke any kind of strong enough force to overcome the tidal stretching: electrostatic charges, for example, are too small to work on macroscopic bodies --- large charges don't persist for long as they attract opposite charges quickly and cancel out. (Besides, as soon as two opposite-charged ring particles meet, I suspect that they'd exchange charges faster than you can sinter the particles together. Once the charges are equalized, there's no more force to hold them together.) The only way of triggering growth in the main rings that I know of is to seed the growth with larger cores which are dense enough to attract the smaller ring particles and hold on to them for long enough for the ices to bond together. Of course, this process is self-limiting. (http://science.slashdot.org/article.pl?sid=07/12/07/1326240)
On the other hand, bodies *with* internal strength have a very different tidal limit. If the strength is similar to what we are used to on Earth, then there's no real reason to worry about Saturn right down to the planet's "surface". (Consider Earth: we're well inside the Roche limit, but satellites (and astronauts!) don't fall apart.)