Several years ago, when I was still at U of Western Ontario, I was browsing through some of the old books in the astronomy section of the main campus science library. One of these dated from the late 1800s and contained a couple of hypotheses, current at the time, that are worth passing along. (I don't think I've posted these before... apologies if I'm repeating myself.)
The first of these had to do with the number of moons around each planet. After Asaph Hall discovered Phobos and Deimos in 1877, no planetary satellites were found for another fifteen years. This book must have been published during that time, because the author pointed out that Earth had one moon, Mars two, Jupiter four and Saturn eight. This had apparently led people to speculate that Uranus had sixteen moons, and Neptune thirty-two, most of them waiting to be discovered. (It seems that Bode's law died very, very hard.) My guess is that this probabaly dates the book to just before 1892, when Amalthea was discovered, as it would have taken people a while to start thinking that all the moons out to Saturn had been found. The death blow came six years later, when Pickering picked up Phoebe.
The second hypothesis was the really neat one. In the late 1800s, Jupiter and Saturn's axial tilts were well known because Jupiter's bands were clearly visible, and of course Saturn's rings provided even better evidence of its tilt. However, since Uranus and Neptune are so bland and so far away, estimates of their axial tilts had to be based on satellite orbits. As a result, although Uranus' axial tilt was pretty well determined, the estimate at the time for Neptune was terribly wrong because it was thought to be same as the plane of Triton's orbit. Since Triton's orbit is circular, everyone (quite reasonably) thought Triton was a regular satellite. In fact, there weren't any irregular satellites known then -- Iapetus and Luna would've had the largest known orbital inclinations. And Proteus hadn't been discovered. So there was no way of telling that this assumption was wrong.
This gave estimates of the axial tilts of Jupiter, Saturn, Uranus and Neptune as 3, 27, 98 and 160 degrees. At this point, someone had the bright idea that there was an unknown process operating in the outer Solar System that was causing the outer planets to flip over from the outside in. I thought this was terrific. Naturally, when better telescopes were invented, this was found to be wrong... but it was still a great idea.
Although it's unscientific to say so, in a way it's always a pity to see a brilliant idea blown out of the water by fact. Nonetheless, even if we can't keep wrong ideas around for sentimental reasons, at least we can appreciate them for the merits they had, given the information that was available at the time.
Old models of planet structure are a lot of fun too, especially the late 19th Century versions which had Jupiter and Saturn still in formation with volcanic surfaces and primordial life. Or then there's the cold Jupiter models from the 1930s, in which the planet formed so slowly the whole planet was frozen and it had an actual surface, with the Red Spot being the last volcano. Ammonia seas were a common feature, though early temperature measurements hinted it was probably frozen.
Adam
The whole 1, 2, 4, ... moons thing gord back awfully far - Kepler thought Mars must have two moons, though I don't believe I've read anywhere who first had the notion that Saturn must therefore have 8.
Although this doesn't strictly deal with Uranus and Neptune, it _is_ an old outer-planet "theory", so I'm dropping it here instead of creating a new thread:
This past week I was in a conference hall where one of the ornamental decorations was a grand piano with an old book sitting on top of it. Of course I had to look at the book and it turned out to be Volume IX of the 1892 edition of Chambers's Encyclopedia. This was the volume that roughly covered the R-S section of the alphabet.
I tried to look up Saturn, but only the mythological god Saturn was listed there. Presumably the planet Saturn was described under "Planets" in volume VIII. However I did run across "Satellites" and found the 1892 estimates for the diameters of Saturn's moons (in MILES):
Mimas: 1000
Enceladus: ?
Tethys: 500
Dione: 500
Rhea: 1200
Titan: 3300
Hyperion: ?
Iapetus: 1800
The really striking thing about this list is of course the vast overestimation of the size of Mimas, listed as being four times larger than its true diameter. I guess this is probably due to Mimas' proximity to the rings; this may have made it difficult for observers to determine its apparent brightness.
Iapetus' estimated diameter here is almost twice the true value as well. This is perhaps understandable; the huge variations in Iapetus' albedo, as observed from Earth, would have made estimating its diameter very difficult.
The other moons listed were Phobos and Deimos, the Galileans, the four biggest moons of Uranus, and the "satellite of Neptune", still without the name Triton attached to it. Amalthea was not included in the chart, but was mentioned in the text -- it was discovered in 1892, so it must have been found just as the book was being typeset. Too late to change the chart! Only the moons of Jupiter and Mars had any diameter estimates given, and they seemed pretty close to the true values, so I didn't copy them down.
Kinda off topic, but in the movie War of the Worlds (1953) They say that Jupiter has a surface with Volcano's!
I recall reading a popular science book by Isaac Asimov back when I was in high school that argued that Jupiter had huge water oceans filled with fish, and advocated commercial fishing there. His science was better when he stuck to chemistry, but generally he was entertaining. One of the more interesting anecdotes he described was of an occasion when he need to know the orbital velocity of particles in Saturn's rings. Basically he played around with the math a bit and suddenly found himself having re-derived Kepler's laws of planetary motion. He rationalized something to the effect that this was a problem which a common person had no hope of solving, a bright person would have remembered Kepler's laws and applied them, but a true genius could safely forget Kepler's laws with the assurance that he could simply re-derive them as needed. Asimov wasn't shy about stroking his own ego. I've always found this little story inspirational, and when taking courses in physics and mathematics tried to make a point of deriving the equations rather than simply memorizing them - and of course learned a lot in the process, and still practice. I tried conveying this notion when I was teaching high school math, but few high school kids have any interest in anything beyond learning the ONE procedure which solved the problem at hand (and these were honors classes, including calculus). Naturally I enjoyed confusing the heck out of them by demonstrating multiple paths to solving a particular problem.
Okay, rambling mode off
"...Asimov wasn't shy about stroking his own ego...."
He referred to that as his "cheerful self appreciation". He did it ostentatiously, with a wink, as a "just between us two" joke and everybody went along with it. People who didn't realise it was half put-on got vastly annoyed by it.
Don't know if anyone can qualify this as an "old idea", but something that I always thought was kind of evocative was perhaps first illustrated in the first edition of Hartmann and Miller's The Grand Tour, in which the interface between Jupiter's atmosphere and postulated liquid hydrogen mantle was literally shown as an ocean surface, lit by lightning. I'm pretty sure general opinion has settled on a gradual transition from gas to liquid, but it was still a cool picture.
I still wonder how gradual that transition really is. Phase changes of material are usually fairly abrupt, so you'd think there'd be a boundary/interface region of some sort...an ocean surface still seems plausible to me.
Another point to ponder is that (IIRC) there are at least three radio-emitting regions on the "surface" of the planet with locations stable enough that they've been used to measure the rotation period. What these are exactly is a mystery indeed...some sort of vulcanism, presumably, but the processes involved must be extremely alien to our perceptions. Heck, you can't really use any geological terms with a straight face when thinking in terms of metallic hydrogen, etc...
[EDIT] To Algorimancer: Yes, Asimov's fiction is worth another try. He can be dull, but I've really enjoyed his stuff when re-reading it as an adult...the fine nuances of his work are much clearer now.
"...are at least three radio-emitting regions on the "surface" of the planet with locations stable enough ..."
These are not on any "surface", other than some magnetic field/plasmasphere interaction "surface" These apparently reflect some of the dynamo-created non-dipole irregularities in Jupiter's magnetic field interacting with the plasma environment of hte planet. These will change with time, but at an arm-waving physical scaling <dimensions and volume> guess, I'd suspect major changes in Jupiter's internal field will take place on time scales of thousands to tens of thousands of years instead of hundreds to thousands, as on Earth.
Actually, if you do the "which of these things is more like another" game, you'd have to say that Jupiter's internal arrangements are closer to the Sun's than to Earth's, and the Sun's internal field dynamics change on the order of tens of years. It would also be easy for me to believe that Jupiter's insides are more dynamic and faster-moving than the Earth's, being made of far less dense gas and plasma than the molten and solid rock, nickel and iron that makes up most of the Earth.
Besides, I have this gut feeling that magnetic fields are derived from the spinning of a transition shell around a planet's (or sun's) core, not by the spinning of the core itself. As entropy progresses and a body slowly cools, the nature of that transition shell both fluctuates in well-developed periods and undergoes basic changes with time, so the periodicities and their characteristics change (slowly) as time goes on.
-the other Doug
Yeah, that's why I placed "surface" in BIG quotes (should've boldfaced them); conventional points of reference just don't apply here...
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