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#11
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Seasons on gas giant moons
Hop David wrote:
SFAIK Saturn doesn't have a powerful magnetic field like Jupiter's. Which mystifies me as it would seem the Saturn also would have a rapidly rotating ball of metallic hydrogen at it's core. http://www-ssc.igpp.ucla.edu/personn...s/sat_mag.html The core is a lot smaller, and the field lined up better with the axis of rotation. Pat |
#12
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Seasons on gas giant moons
"Doug..." wrote:
says... snip Is there a mechanism that suggests that large terrestrial moons would be more likely to form *close to* a gas giant? The only examples we can look at closely (at least comparatively closely) are the gas giants in our own solar system, and their moons. Yeah. I've seen theorizing, though, about what kind of formations we could expect in different star systems -- broad generalizations that tried to explain why we see what we do in the Solar System. Some of those generalizations turned out to be wrong, of course, such as the idea that gas giants forming close to their parent star would be exceedingly rare; the notion was that the parent star would tend to accrete most of the available material before a gas giant could really form nearby. Studies are just beginning to show that that theory may have been wrong. Of course, it's awfully hard to make solid predictions with the limited observational data we have available, so one must take them with a grain of salt... but I was wondering if anyone had heard of reasons why terrestrial planets forming far away from a gas giant might be expected to be unlikely. It will be enlightening to see what theories arise and develop as our understanding of extrasolar planets increases (though, as you say, we may *still* not arrive at a definitive answer). We live in an interesting time. Of course, there is the problem that a hot Jupiter might just gather all of the heaviest elements into itself, leaving only the lighter elements for aggregation into its moons -- in which case, achieving gas giant moons of terrestrial composition might be impossible. I'm sure you can come up with models for both cases -- it will probably have to wait until we can investigate other planetary systems far more closely before we can know anything for certain. Of course. Still, speculation is interesting. And that isn't likely to happen in our lifetimes, unless we develop an FTL drive in the next couple of years. Well, barring some kind of revolutionary theory that reshapes our understanding of physics, I don't see that happening; we don't even have firm evidence that FTL travel is *possible*, let alone developing the wherewithal to put it to use. More's the pity, though. -- Best regards, Matt Funke |
#13
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Seasons on gas giant moons
Doug... wrote:
Can you imagine living on such a moon, though? On one side of the thing, the primary would hang like a huge, baleful presence, dominating the sky and everything under it. On the other side, there would just be the alternation of the sun, stars and other moons. Such a dichotomy would have profound effects on any civilization that arose there. Some non-arbitary marks on our globe: North and South poles and the equator. The moon would also have a north and south pole & equator. And there'd be four non arbitrary points on its equator: Gas giant pole (point closest to the primary), anti gas giant pole, & two points on the equator 90 degrees from these. The six points would define 3 great circles (of which the equator is one). Their globe would be marked like an octahedron. The planet side would have frequent and long solar eclipses during the spring and fall equinox and be eclipse free the summer and winter solstice if the orbit plane is tilted enough. Midnight during the spring and fall equinox would be of special significance: The moon's shadow would be cast onto the center of the gas giant as viewed from the moon's inhabitants. -- Hop David http://clowder.net/hop/index.html |
#14
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Seasons on gas giant moons
Matthew Funke wrote:
Some of those generalizations turned out to be wrong, of course, such as the idea that gas giants forming close to their parent star would be exceedingly rare; I remember being delighted by that news. A favorite fantasy of mine is a Gas giant In an Earth Like Orbit (Gielo) with an Earth Like Moon (Elm). http://clowder.net/hop/gofix/artifact.html -- Hop David http://clowder.net/hop/index.html |
#15
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Seasons on gas giant moons
Hop David wrote:
The planet side would have frequent and long solar eclipses during the spring and fall equinox and be eclipse free the summer and winter solstice if the orbit plane is tilted enough. Midnight during the spring and fall equinox would be of special significance: The moon's shadow would be cast onto the center of the gas giant as viewed from the moon's inhabitants. This could lead to some very interesting breeding and migration cycles in regard to such a planet's wildlife; assuming more than one moon (with a gas giant that seems a very reasonable assumption, based on Jupiter and Saturn) and the night sky would be a very interesting place indeed...think of the strange religious beliefs that might evolve regarding just what was going on overhead; our star-like appearing planets generated a great deal of mythology just by their movement; imagine what ones that become visible disks would do in this regard- are they moving closer and further away, or are they shrinking and growing in size? In fairly short order the first would be suspected to be the case, based on the apparent reduction in size of people seen at a distance. A hypothetical civilization on such a planet might have a fairly accurate idea of true cosmology at a far earlier stage of its evolution than any Earth civilization did. Imagine nomadic hunter-gatherers with a understanding of a sun-centered universe with multiple worlds... is one of the other moons where you go when you die? Io would make a pretty good hell. Pat |
#16
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Seasons on gas giant moons
Pat Flannery wrote:
indeed...think of the strange religious beliefs that might evolve regarding just what was going on overhead; our star-like appearing planets generated a great deal of mythology just by their movement; imagine what ones that become visible disks would do in this regard- are they moving closer and further away, or are they shrinking and growing in size? In fairly short order the first would be suspected to be the Well.. would it really be all that different from our moon (which is much more active in beliefs than mere planets) except there would be more of them and on different schedules? case, based on the apparent reduction in size of people seen at a distance. A hypothetical civilization on such a planet might have a fairly accurate idea of true cosmology at a far earlier stage of its evolution than any Earth civilization did. Imagine nomadic hunter-gatherers with a understanding of a sun-centered universe with multiple worlds... is one of the other moons where you go when you die? I'm not certain that would happen, or at least happen considerably earlier than on Earth (where it didn't really happen all that late either). But yes, going to another Moon when you die sounds liek a resonable guess. Io would make a pretty good hell. Pat -- Sander +++ Out of cheese error +++ |
#17
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Seasons on gas giant moons
Sander Vesik wrote:
Well.. would it really be all that different from our moon (which is much more active in beliefs than mere planets) except there would be more of them and on different schedules? Assuming we are both talking about other moons viewed from an inhabited one in orbit around a gas giant, there would be a major difference- our Moon undergoes phases and an occasional eclipse, but it stays the same size in the sky (although it still looks bigger to me when it's on the horizon...I know it's not... but it looks bigger anyway); but the moons in orbit near the inhabited one would appear in the sky as bright stars when they are far away, but become visible discs like the Moon as they drew close to the inhabited one in their orbits. The planets in our solar system vary in position and brightness to the naked eye, but the only two things that can be seen as discs in our sky (the Sun and Moon) stay the same apparent size all the time (the Moon varies a bit, but probably not enough to be very noticeable). Now put yourself in the position of an observer on our hypothetical inhabited moon- the sky is a very complex place; assuming that your planet is tidally locked, then on one side of the moon, you've got the big gas giant hanging pretty much motionless in the sky, but changing its phases as you orbit around it; given it's size, you probably get very frequent eclipses of your system's sun; but there are two other groups of odd objects in the sky- the other moons of your gas giant, and the other planets in your solar system. The moons inboard of you probably cross in front of the gas giant quite often, and their shadows can be seen falling on the gas giant; in fact _your_ moon's shadow can probably be seen falling on the gas giant- and once you make the connection between _that_ shadow and the ones the other moons are casting, the realization sinks in that those discs in the sky are worlds like the one you are living on. Then there are the other star-like moving objects to contend with- the star's other planet; their motion is noticeably different from the moons, and this soon would also start speculation as to what they were. Remember the contortions that philosophers went through in an attempt to make a geocentric cosmos work? Those would look simple compared to what one would have to go through to make a moon-centered one work! You'd end up with something with as many layers as a onion hooked together in incredibly convoluted ways- the whole thing would be so complex to even try that I'd bet that it never would be even seriously considered before the correct sun-centered view arose. case, based on the apparent reduction in size of people seen at a distance. A hypothetical civilization on such a planet might have a fairly accurate idea of true cosmology at a far earlier stage of its evolution than any Earth civilization did. Imagine nomadic hunter-gatherers with a understanding of a sun-centered universe with multiple worlds... is one of the other moons where you go when you die? I'm not certain that would happen, or at least happen considerably earlier than on Earth (where it didn't really happen all that late either). But yes, going to another Moon when you die sounds liek a reasonable guess. I'll bet they would probably think that all the other moons had life on them of one sort or another. Pat |
#18
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Seasons on gas giant moons
Pat Flannery wrote in message ...
[snip] Remember the contortions that philosophers went through in an attempt to make a geocentric cosmos work? Those would look simple compared to what one would have to go through to make a moon-centered one work! You'd end up with something with as many layers as a onion hooked together in incredibly convoluted ways- the whole thing would be so complex to even try that I'd bet that it never would be even seriously considered before the correct sun-centered view arose. Not only that, but don't forget the planet looming over half the moon. It would be many times larger than the full moon and would hang nearly motionless in the sky (due to tidal locking). That sorta thing leads away from a "my local spot is the center of the universe" concept. And once you've demoted your own planetary body from the center it's much easier to continue from there, so even if you start thinking the planet is the center of the universe you can more easily and naturally move to a Sun centric model once you have basic data. Compare, for example, the shift from geocentric to heliocentric to the shift from heliocentric to galactocentric etc. Plus, you can do the kind of astronomy Kepler and Tycho did with your bare eyes. |
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