The moon on the dark side

[peacekeeper]

<blockquote><font class="small">In reply to:</font><hr /><p>If your moon is in permanent eclipse, it's going to be very very cold if it has to rely on the star's warmth.<p><hr /></p></p></blockquote><br />Well, the point is to have the gas giant orbit very close to the star, and hence be warm enough to radiate enough heat to the moon. I was just not sure whether a red dwarf could supply all that heat to the gas giant, but the more I think about it, the more I realize it probably could. After all, it <i>is</i> a star we are talking about, red dwarf or not...<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>Your moon would also experience significant tidal heating as it wobbled around in a halo orbit<p><hr /></p></p></blockquote><br />Could you please explain this more throughly? It sounds like an interesting point, so it annoys me that I don't quite understand what you mean.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>How many eyes does your species have? We only have two, so perhaps that's why I think our gas giants are beautiful.<p><hr /></p></p></blockquote><br />My species have four eyes. Perhaps that's why I prefer gas giants such as this one. Of course, that's just an artist's impression, but I have no doubt such worlds actually do exist.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>a gas giant that is radiating strongly in the infrared is likely to be even more bland than our gas giants<p><hr /></p></p></blockquote><br />The <i>colors</i> of a gas giant mostly depend on its gases though, don't they?<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>A white dwarf has a beautiful, blue-white actinic arc-lamp quality to its light.<p><hr /></p></p></blockquote><br />Now when you mention it, I have to agree with you. They truly are beautiful.

 

[heyo]

Something just caught my eye....<br /><br />bobvanx wrote:<br /><i>....Neptune gives off heat as it makes a rain of diamonds, for example. </i><br /><br />Come again??<br /><br />Heyo<br />

 

[peacekeeper]

Yes, I kinda wondered about that too. Since it wasn't important for the topic at hand though, I refrained from asking about it. But please bobvanx, should you ever return to read this thread again, please feel free to answer that as well <img src="/images/icons/laugh.gif" />

 

[kmarinas86]

Just dude the search and you'll find the answer:<br /><br />http://www.google.com/search?hl=en&q=rain+diamonds+neptune

 

[bobvanx]

Thanks for the link to the search for Neptunes' diamonds, k_m.<br /><br />PeaceK and Heyo, after enough years of following the scientists around, my brain is just filled with trivia like that. Another thing that's up here is black body radiation and emission spectroscopy, both of which would contribute to the perceived color of your gas giant, PeaceK. Black body radiation describes how a perfect radiator starts black, goes red, yellow then white hot. Your planet will have to radiate strongly in the infrared in order to warm your moon, and as you note, this could be heat gathered on the sunlit side of your gas giant (and radiated as it spins on its axis).<br /><br />Okay, let's see here: If the gas giant is re-radiating heat to the moon, that could be non-specific enough that it wouldn't jolt readers out of the story. Those "hot Jupiters" have temperatures in the thousands, so there is certainly plenty of radiant heat there.<br /><br />Bland: my thought here, which could be entirely incorrect, is that a warm/hot gas giant would be so thouroughly "mixed" that the gasses wouldn't be distinct. I bet you could go either way on this and find data to support your theory.<br /><br />A) The atmosphere is so turbulent it is well-mixed and of uniform color. The re-radiation is in the oranges and reds through the infrareds. or,<br /><br />B) While the upper atmosphere is very hot, the planet itself is much cooler and so giant convective cells create truly awesome color bands and eye-spot storms. The hot zones are radiating so strongly in the oranges and yellows, but the rest of the planet is dark and cool.<br /><br />===========<br /><br />tidal heating<br /><br />Since humans are coming in to this system and then using some sort of future tech to stabilize the moon in shadow, you've got to assume a really good reason for doing so. Was the moon in a stable but chaotic orbit? Was it in a resonant orbit? In any case, as it tries to follow celestial mechanics, and your future tech prevents it fro

 

[heyo]

You're right about that.<br /><br />I think though, even if the planet is warm or hot, if there are temerature gradients, you could probably get convection.<br /><br />Heyo

 

[peacekeeper]

Thank you for that very interesting answer, bobvanx. You really seem to know what you are talking about.

 

[bobvanx]

You're welcome!<br /><br />heh />>really seem to know<br /><br />yeh, be careful not to take any of it too seriously. I don't know what I don't know. Hanging out on these boards educates me quite a bit.

 

[bobvanx]

>> temperature gradients and convection<br /><br />That's my thinking, that the overall vertical gradient is the deciding factor. If there is heating coming into the atmosphere from both the interior and the extrior, the energy is going to be driving powerful jet streams, cloud bands and eye storms. I don't have the math to work it all out. My instinct is that you could cross a threshold at which point the uppre atmosphere uncouples from the lower, and behaves in a more star-like manner as it roils and boils.<br /><br />The only reason it's important is that we are trying to throw enough heat at the moon to make it warm.<br /><br />That reminds me; the back side of your moon is going to be at the temperature of deep space. If it has an atmosphere, there are going to be some powerful winds around the terminator as the air rushes to the back, dark side, turns liquid, falls out of the sky and freezes out.

 

[peacekeeper]

First, what's a temperature gradient?<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>If there is heating coming into the atmosphere from both the interior and the extrior, the energy is going to be driving powerful jet streams, cloud bands and eye storms.<p><hr /></p></p></blockquote><br />Well, I don't mind those things. The important thing is that the planet to the greatest part consists of nice and shiny colors in the red, blue or green spectrums. Preferably red.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>the back side of your moon is going to be at the temperature of deep space.<p><hr /></p></p></blockquote><br />Not really, no. The moon will not be tidally locked, and it will have an atmosphere thick enough to protect it from radiation, so I expect no greater difficulties with the weather.

 

[bobvanx]

A temperature gradient merely describes how much difference there is from the cold place to the hot place. A greater difference drives more powerful forces. On Earth, a hurricane that forms in a "steeper" temp gradient carries more energy; it's bigger, winds are stronger, and so on.<br /><br /> />>preferably red<br /><br />Yes, red is good for your gas giant, people are likely to accept that it is warming your moon if it is red. Even a world with obvious, striking color bands, if it is glowing with black body radiation in the red portion of the spectrum, is going to look uniformly colored on the night side. On the sunlit side, the white light would overwhelm the red light, and you'd see all its colors.<br /><br /> />>not tidally locked<br /><br />Interestingly, there's a precedent for that in SF. Can't recall the story, but in it Earth is moved into an orbit around Jupiter. It retained its 24 hour day (it would actually begin to slow down as Jupiter worked to stop it). I want to say its by someone authorized by Larry Niven's estate.<br /><br />Anyway, if your moon were originally in a resonant orbit, say three rotations around the gas giant to every two of the gas giant around the star, then the moon would start out both very hot (getting direct sunlight) and with a rotational period of 1.5 "days" to each of the gas giant's "years." Moving it into the semi-stable shadowed LaGrange point wouldn't change this rotational period. It would cool it down to habitable temperatures.<br /><br />It would add to your tidal heating though. <br /><br />Hmmm.... this moon could even start out being its own minor planet, in a cometary sort of orbit (highly eccentric), which would be stable over a long period. Deepest part of the orbit (aphelion) way out where it ices up nicely, perihelion near enough to the gas giant that it gets a good orbital kick. Your people happen to arrive at a time when a few careful nudges help it settle into the shadow of the gas giant. Then you could pick whate

 

[peacekeeper]

Thank you very much for those suggestions and ideas.<br /><br />Could you please tell me which colors the various gases would correspond to?

 

[nexium]

Thank you for the very interesting thread. I started to tell you about the solar synchronous orbit, then decided it did not apply to this. I'm guessing, but I think a solid planet such as Mercury could be as big as Jupiter. Solid might mean it could be very close to the star without being torn apart because it was inside the roache limit. The gravity might be 100 times that of Earth as it would have several times the mass of Jupiter. Very close might mean very little atmosphere. It and it's inhabited moon could both rotate on their axis at any desired speed up to perhaps 10,000 MPH at the Equator which is about ten times the speed of Earth's equator. I'm still sitting on the fence as to whether a continous total eclipse of the sun is possible as viewed from the inhabited moon.<br /> Lets assume a continous annular eclipse is possible with 80 to 90% of the sun's disk blocked. Some wobble seems likely, so energy levels reaching the moon might be dangerous, locally and occasionally requiring the inhabitants to seek shelter.<br /> The sun needs to be main sequence K, G or F for humans to perceive color except in a perverse manner. An exception would be a compact star that had cooled to approximently the right color temperature. In the case of a very massive black hole the light would come entirely from the accreation disk. Low mass black holes produce mostly very dangerous radiation such as gamma rays in their accreation disk, so low mass black holes won't do for your story. The energy from an accreation disk can double or halve in less than a year.<br /> A class M star is sometimes called a red dwarf. They produce moderate heat, but almost no light, but I don't think you can get close enough for it to be too hot, unless the planet and moon have increadible adhession and cohession. At 1/10 th the roache distance, the tidel forces are extremely strong. Neil

 

[bobvanx]

>>colors<br /><br />No, unfortunately. It's been too long. I used to know many, and still know a couple... neon glows red, argon blue/white) and sulfur compounds are nearly any shade of oranges and reds you want (there are greens, too), chlorine is green/yellow, flourine is yellow/brown... If you've seen sodium vapor lamps, you know they glow that weird monochromatic yellow/orange... <br /><br />But the relationship between what color the gas is at "atmosphereic" pressures, taken along with what colors they become as they are excited by high temperatures and/or electricity, is information lost to me.

 

[rfrank1399]

since this is fictional, why not have the gaseous planet have a rotational tilt 180 opposite of what earth has. then you might get by saying the moon is "trapped" in the mangnetic gravataional forces at the pole of the gaseous planet........

 

[peacekeeper]

True. The problem with that is that the planet would not actually be spinning in relation to the moon, and would hence be less likely to be able to provide it with sufficient heat, I think.

 

[igorsboss]

If the planet had a large magnetic field, the moon might encounter the planet's magnetotail once in a while.<br /><br />That might make for some interesting magnetic storms on the moon. Since the moon would have an atmosphere but lie in dim light, the aurora might become visible and very spectacular.<br /><br />In fact, the aurora might not be bound to the poles, as they are on Earth. They would occur whereever the planet's magnetotail intercepts the moon's atmosphere.<br /><br />Could make a nice romantic SciFi view...