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Seasons on gas giant moons



 
 
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  #11  
Old April 21st 04, 06:42 PM
Pat Flannery
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Default 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  
Old April 21st 04, 09:35 PM
Matthew Funke
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Default 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  
Old April 23rd 04, 06:41 AM
Hop David
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Default 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  
Old April 23rd 04, 06:51 AM
Hop David
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Default 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  
Old April 23rd 04, 07:26 AM
Pat Flannery
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Default 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  
Old April 25th 04, 09:27 PM
Sander Vesik
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Default 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  
Old April 26th 04, 01:40 AM
Pat Flannery
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Default 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  
Old May 2nd 04, 06:32 AM
Christopher M. Jones
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Default 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.

  #19  
Old May 2nd 04, 03:24 PM
Earl Colby Pottinger
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Default Seasons on gas giant moons

(Christopher M. Jones) :

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.


With the ability to ensure world-wide timing of measurements (IE the
terminator on the Gas planet crossing certain long term features on the gas
planet) you can take multiple measurements (long baseline) of the other moons
and very accurately calculate thier speed and positions in a short time frame
and with very early tech.

Earl Colby Pottinger

--
I make public email sent to me! Hydrogen Peroxide Rockets, OpenBeos,
SerialTransfer 3.0, RAMDISK, BoatBuilding, DIY TabletPC. What happened to
the time?
http://webhome.idirect.com/~earlcp

 




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