Celestia Forums

Here is an interesting question that was brought up a while back that I never fully followed up with. If everyone doesn?€™t already know I have been working on a system that I am trying to keep it as real as possible. More information can be found at http://www.celestiaproject.net/forum/viewtopic.php?t=2448

The major planet in the system is called Gigus it very unusual in that it is tipped ~90 degrees off access. But what is more, I guess I would use the word amazing, is that the pole is tidally locked to the main star Rylix. Such a pattern has never been seen in large body objects, however there are known asteroids that are rotating on more then one axis. So I guess the question is, ?€?Is it possible to have such a massive planet, spinning at such a fast rate of, and still be able to keep the pole locked on the main star.?€

To the extent that it is defying a basic physical "law" -- conservation of angular momentum -- there needs to be some external force that is twisting its polar axis. Given the mass of the planet, this has to be a very large force, indeed. I'm not at all sure how this would be generated. A black hole, maybe?

The continuous change of direction of the rotational axis would be causing gigantic vortices in and on the planet, too. As a result, its temperature would be quite high.

it'd basically be impossible, even more so given that the gas giant isn't subject to any appreciable tidal forces. Heck, normal tide-locking would be impossible too unless the giant was extremely close to its star in a very old system - jovians are VERY hard to tide-lock because of their largely fluid interior.

?€?Is it possible to have such a massive planet, spinning at such a fast rate, and still
be able to keep the pole locked on the main star??€

I think given that the inner system has habitable worlds, there is NOT a magnetar lurking around here...

GlobeMaker wrote:Yes. I do not believe that "tidal" forces could keep this configuration for more than one orbit for a Jupiter-like planet. But magnetic forces can do it.

NO! Please do not keep answering these science questions when you clearly don't have the foggiest idea about the physics involved!!

Magnetic fields would be totally incapable of changing the planet's physical orientation. Even if they were in the extraordinarily unlikely configuration that you specified - the forces involved are just too small to affect the physical body of the planet.

The only thing that could possibly change a planet's orientation is tidal interaction (or an almost-planet destroying impact to physically tip the planet over, like the one on Earth that formed the Earth's moon). However, in this case tidal forces would not be able to keep the planet in the specified orientation - in fact they'd be working full time to keep it OUT of that orientation since it's tidally very unstable.

The star Rylix is estimated to need a magnetic flux density at
its surface of 10^46 Tesla to keep the 91 degree tilt of
Gigus pointed at the star permanently.

You can check my figures with these links :

http://en.wikipedia.org/wiki/Magnet
http://dept.physics.upenn.edu/courses/g ... _1999.html
http://webpages.charter.net/griche/pt/u8s2prb.htm

Here are the calculations :

r = 7.9 x 10^7 meters for Gigus radius
m = 1.6 x 10^28 kg for mass of Gigus
w = 3.12 x 10^-5 radians per second for Gigus spin rate
dt = 3 x 10^8 seconds = half an orbit period for Gigus
u = 10^-6 Henrys per meter = permeability of free space
d = 7.44 AU = 1.6 x 10^11 meters = orbital distance of Gigus
M1 = 6 x 10^-3 Tesla = magnetic flux density (B) of Gigus (85 x Earth's)
M2 = the unknown B of Rylix

I = .4mr^2 moment of inertia for sphere
L = Iw = angular momentum of Gigus = 4 x 10^43 kg meter^2 / second
F = M1 x M2 / (ur^2) approximate force between two magnets

torque = dL/dt needed to rotate the Gigus along its axis
dL = 2L to reverse its spin
torque = force x distance = 2.7 x 10^35 Joules
distance = sin(1 degree) x r = 1.4 x 10^6 meters
force = torque/distance = 2 x 10^29 Newtons = F

M2 = Fur^2/M1 = 10^46 Tesla (approximately)

But this will also attract Gigus towards the star, so the
orbital velocity will need to be faster to balance this
extra attraction that occurs in addition to gravity. I will
leave that calculation for tomorrow, after the responses
come in. If I have made a mistake in this estimate, please point
out which section is wrong so I can adjust the result to be
more accurate.

Thanks for all the feedback

GlobeMaker I have noticed one small problem though in the energy requirement.

The total solar output is only about 5.0x10^26 Joules a second or better put if my math is correct, that?€™s about 1x10^17 too little power for the magnetic theory to work. Now if the main star was a black hole then that is a different story.

So it looks like I am back to having a static polar planet, I guess the next question is tipped or not, if so how much and what about the color. The purple a little too much? I am sure there is some chemical makeup that might produce the color, but then again is it plausible?

And as I said, GM's calculations are completely irrelevant because that situation is completely unrealistic. You can't tip planets over using magnetic fields in any kind of remotely realistic planetary scenario, period.

Ok next questions about the plant, it?€™s actually a two part question.
1. Because the planet is so massive it has entered the estimated range of a brown dwarf between 8 and 13 J-masses. What would the radius be on such a planet be. I have heard the Jupiter is about as large radius wise as you can get before the gas just keeps on piling on but the radius will not change that much. A density of 7.90g per cm^3 seem high especially compared to some rocky bodies.

2. Is what would its color be? Could it be the magenta/purple that I have suggested?

Planet Stats

MKruer wrote:Ok next questions about the plant, it?€™s actually a two part question.
1. Because the planet is so massive it has entered the estimated range of a brown dwarf between 8 and 13 J-masses. What would the radius be on such a planet be. I have heard the Jupiter is about as large radius wise as you can get before the gas just keeps on piling on but the radius will not change that much. A density of 7.90g per cm^3 seem high especially compared to some rocky bodies.

8-13 J-masses isn't enough to qualify as a brown dwarf - it'd be a superjovian. It needs to be at least 13 J-masses to be a BD.

A 15 MJ brown dwarf when it forms (well, once it stops its main contraction anyway at about 500 million years of age) is about 80,000 km radius. But BDs actually SHRINK over time - 5 billion years later it'd be about 70,000 km in radius due to gravitational contraction.

Not sure how big a superjovian of 8-13 MJ would be... I'd guess it'd be around 80,000 km, you're right in that gas giants don't get all that much bigger in radius than Jupiter. It'd still be emitting some heat, but not from deuterium fusion (it's not massive enough) - it'd all be from gravitational contraction.

2. Is what would its color be? Could it be the magenta/purple that I have suggested?

All depends on the atmospheric chemistry. Undoubtedly it'd be similar in composition to Jupiter and Saturn (lots of H2 and He), but they're coloured by things like ammonia and hydrocarbon clouds. purple/magenta seems a bit unlikely - if it was a bona fide BD then it'd emit a lot of IR radiation that could give it a dim red/purpleish glow, but it's not massive enough. I'm not sure what compounds would give a planet a 'natural' purple/magenta cloud colour, I suspect it'd be more likely to be red/orange/yellow/brown.

Hello MKruer, I agree that you should use a static polar planet. I want to
correct the numbers you calculated where you said, "The total solar output
is only about 5.0x10^26 Joules a second or better put if my math is correct,
that?€™s about 1x10^17 too little power for the magnetic theory to work."

I assume your stellar power figure is correct without checking " 5.0x10^26 Joules a second ".
But a correction follows for your calculation of the ratio that describes the shortfall of power.

5.0x10^26 Joules per second is 5.0x10^26 watts. To get the energy (Joules) multiply by time
dt = 3 x 10^8 seconds = half an orbit period for Gigus
5.0x10^26 watts x 3 x 10^8 seconds = 1.5 x 10^35 Joules during a half orbit.

So that is close to the torque energy of 2.7 x 10^35 Joules.

The star needs 2 times as much power to supply the torque, not 10^17 times as
much power. I have made these calculations to improve my level of education concerning
torque, angular momentum, and magnetism. Thank you for providing the scenario in which
the calculations are interesting to someone. This concludes my discussion of Planetary Torque.

To get a purple color, please check into the element Manganese
http://www.rhiw.com/lluniau_pages/image ... neigwl.jpg

Thank you again for this stimulating discussion of your fictional planets.

Your humble associate, Alan Folmsbee, MSEE

I wonder if I'm the only one here who finds Globemaker's contributions here to be somewhat infuriating. Especially his misleadingly authoritative lecture style - it's quite clear that he doesn't actually understand how planets behave and what fields can influence them.

The thing you have to realise is that it's not enough to throw numbers around - you have to actually understand the situations in which they'd be relevant. It seems pretty clear to me that while you may have some understanding of engineering, you have very little actual comprehension about planetary science (and believe me, having worked as a planetary scientist, especially on orbital dynamics, I know a lot more about the subject than you do).

Gravity is a much stronger force over large distances than magnetism - that is a basic, fundamental, physical fact. It is therefore most likely to be the dominant force in any interaction between two massive bodies. Since the stellar magnetism is strongly coupled to the rotation axis, not only would Gigus have to be tipped toward the star but the star would also have to be tipped toward Gigus for its pole to point toward it. And that means the star has to be tipped on its side too - and also somehow magnetically locked so that it pointed to Gigus all the time (which also can't happen). So how would you explain that? Why wouldn't the other planets orbit around the star's equatorial plane too? How could the magnetic field dominate over gravitational influences? It can't, under any remotely realistic scenario.

GM's scenario simply can't happen in reality. Magnetic fields cannot in any realistic scenario tip a planet so that it points towards a star all the time. If you're educating yourself about this scenario, then at least learn that.

10^46 Teslas is really strong.

http://en.wikipedia.org/wiki/Tesla_%28unit%29

The page says:

"# maximum theoretical field strength for a neutron star, and therefore for any known phenomenon, 10^13 T."

Is that ok? For a sunspot, it gives only 10T.

Malenfant wrote:

MKruer wrote:Ok next questions about the plant, it?€™s actually a two part question.
1. Because the planet is so massive it has entered the estimated range of a brown dwarf between 8 and 13 J-masses. What would the radius be on such a planet be. I have heard the Jupiter is about as large radius wise as you can get before the gas just keeps on piling on but the radius will not change that much. A density of 7.90g per cm^3 seem high especially compared to some rocky bodies.

8-13 J-masses isn't enough to qualify as a brown dwarf - it'd be a superjovian. It needs to be at least 13 J-masses to be a BD.

A 15 MJ brown dwarf when it forms (well, once it stops its main contraction anyway at about 500 million years of age) is about 80,000 km radius. But BDs actually SHRINK over time - 5 billion years later it'd be about 70,000 km in radius due to gravitational contraction.

Not sure how big a superjovian of 8-13 MJ would be... I'd guess it'd be around 80,000 km, you're right in that gas giants don't get all that much bigger in radius than Jupiter. It'd still be emitting some heat, but not from deuterium fusion (it's not massive enough) - it'd all be from gravitational contraction.

2. Is what would its color be? Could it be the magenta/purple that I have suggested?

All depends on the atmospheric chemistry. Undoubtedly it'd be similar in composition to Jupiter and Saturn (lots of H2 and He), but they're coloured by things like ammonia and hydrocarbon clouds. purple/magenta seems a bit unlikely - if it was a bona fide BD then it'd emit a lot of IR radiation that could give it a dim red/purpleish glow, but it's not massive enough. I'm not sure what compounds would give a planet a 'natural' purple/magenta cloud colour, I suspect it'd be more likely to be red/orange/yellow/brown.

Well last time I read, they were at a miss about what mass was necessary, and gave the range 8-13. However I have heard the 13 J-masses coming up more and more frequently as the lower limit. I guess the real question that should be asked is what would be the required average planetary density for fusion to begin.

When I originally designed the system I though ?€?Wouldn?€™t it be cool if?€¦?€

Hi Brendan,

Yes, you are right. I agree with you and your reference. The calculation of
10^46 Tesla needed to keep a Jupiter-like planet with its axis pointed at
the star indicates that it is not realistic for MKruer to propose this motion
for a planet. MKruer has said he is abandoning that goal. He will now use
a planet that has its axis in a direction that is not changing. We all believe
that there is no realistic magnetism or tidal forces that are strong enough
to keep the pole pointed at the star during the orbits. Thank you for
pointing out the limiting magnetic B field for a neutron star.

MKruer wrote:Well last time I read, they were at a miss about what mass was necessary, and gave the range 8-13. However I have heard the 13 J-masses coming up more and more frequently as the lower limit. I guess the real question that should be asked is what would be the required average planetary density for fusion to begin.

8 MJ is definitely too low.
And it's really about mass, not density - the mass is high enough (given the fact that the radius doesn't really increase correspondingly with mass, due to compression) that the internal density is enough to start fusing.

I then concluded that if the plant was just as that stage it would be emitting a lot of IR radiation and be able to give it the purple glow. So at least we are in the same mind set.

Bear in mind that it also depends on age. If your system is a few billion years old, a low mass BD is only going to have a total luminosity (mostly IR) of about 0.0000003 or 0.0000002 Sols. And it probably won't be visibly glowing at all by then.

So what you are getting at is the light purple might be a bit much, but a darker purple color might be more plausible.

Well, the purple is going to be a *glow*, not a natural colour of the clouds. There could be purple compounds that might colour the clouds, maybe they could only be stable at warmer temperatures or something (in the interior of the planet) - but you'll still probably have icy clouds high up even though an 8 MJ world is a superjovian. Those would be paler.

But really it depends on the chemistry involved. I'd guess that purple clouds aren't impossible though, through some form of weird organic chemistry (Manganese would be very unlikely, btw - it's a rare element, cosmochemically speaking)

Would iodine be able to color the clouds purple if there were enough of it? Webelements gives abundances of one ppb by weight and 0.01 ppb by atoms in the universe, so it'd be hard to do this coloring.

Brendan wrote:Would iodine be able to color the clouds purple if there were enough of it? Webelements gives abundances of one ppb by weight and 0.01 ppb by atoms in the universe, so it'd be hard to do this coloring.

You shouldn't be looking for elements, you should be looking for compounds.

ammonia, methane, and sulphur compounds can colour the atmosphere. Methane absorbs red light, which is why Uranus and Neptune are blue (there's more methane in their atmospheres than in Jupiter and Saturn's).

Saturn's atmosphere seems to be blue in places as well as yellow (see http://science.nasa.gov/headlines/y2005 ... saturn.htm ), though mostly the planet is yellow. Jupiter is to the naked eye mostly yellow with brown/reddish bands. These colours are mostly caused by ammonium and sulphur compounds (reds might be phosphorus?) rising from the interior. ( http://www.space.com/reference/brit/jup ... imate.html )

A superjovian would probably have the same sort of compounds, maybe the chemistry might be a bit different in the warmer interior though. The atmosphere is likely to be very active, with lots of well-defined bands and spots and strong winds driven by the heat from within (so it'd look basically like jupiter). Iodine would be a no-no, it's just too rare. It's unlikely that the greens/blues of methane would be a dominant colour since that seems to be something associated with the smaller icy giants (Uranus and Neptune) rather than the full-on hydrogen giants (Jupiter and Saturn), and a superjovian probably would be more like the latter.

Again though, I don't know enough about chemistry to specify compounds that you're likely to find in such an environment that may be purple in colour. I'm also not sure if it might be possible for scattering from another gas to cause a purple colour in the same way that methane produces a blue colour.

Globemaker, I just want to take issue with your signature:

GlobeMaker wrote:while(everythingYouSay==TRUE){return(0);}if(++time<demise)return(*argv[++facts]);

Surely what you mean is:

while (++time<demise){while(everythingYouSay==TRUE){return(*argv[++facts]);}}return(0);

:wink: