Oh, EDG
How we miss thee
I have too many stars that all end in "D"
And my Agro worlds are all freezy
And the bright stars put out UV
Oh, EDG
I wrote TNE
But my solutions came out creaky
I'd like to know, so I can grade me
What I missed, so indiscreetly
Oh, EDG
Come to save me
My chaotic thoughts should be tidy
Are the hab zones still good really?
And is this song really funny?
Oh EDG
Heed my little plea
Dee-dee-dee-dee
Dee-dee-dee-dee
> Ø Oh look, there's Alell. Never mind, DED, we found it.
>
>
>
> Oh look, there is a big ol screw-up on me.
>
>
>
> The physical characteristics of Alell are 467. So, yes, indeed, it should
> have had one of its stars increased to be F-K. I probably should have made
> it have stellar data of K7V M7V. I dunno why I screwed it up. Maybe I
> thought two M7Vs in a tight formation would have produced enough heat?
> Regardless, I should have definitely bumped it. Maybe I could have swapped
> it around with Boughene and make Boughene be an M7V, and Alell be a K7V
> M7V
> so as to try and keep the distribution a little more like the original.
>
>
>
> On a related through, I noticed in your reply to DED that Frank hated the
> high-pop hostile world. I really hate those, too, and (with the horrible
> upheaval even in the Domain of Deneb/Regency) used that as an excuse to
> ruthlessly crush many (maybe most) of those worlds. (In fact, I initially
> went too far and ended up putting some of them back.)
>
>
>
> Mike West
>
>
>
>
>
>
But anyway - if you can write some specific questions then I can try answering them (I'm not particularly inclined to read 75 messages to find out what they are!)
Thank you for the response. I have no idea why no one else asked any questions, but if you are willing, I have a few.
Basically, we were discussing about habitable planets, how to get them, and what the stellar implications were. My basic position was that for a planet to have an nitrogen/oxygen atmosphere (i.e. atmosphere codes 2-9;D-F, or at least 4-9) requires some kind of biosphere that took a really, really long time to develop. If a world had no life, the oxygen wouldn’t be in the atmosphere. Since that level of oxygen takes so long and takes at least some kind of life, that means such a planet really needs a reasonably stable star, meaning likely one of F G K M main sequence. Obviously, the ancients can influence this, but there *were* only 400 of them (even if they controlled billions of subjects, there were only 400 of them), and even then there is only so much they can do over their 10,000 – 20,000 years of activity.
Questions around this, are:
- Is the above even remotely close to correct?
- Granted, we only have a sample of 1, but is it feasible for primitive life to generate an appreciable oxygen atmosphere over 300,000 years? Or would it take millions of years?
- If a world had a type 6 atmosphere, but lost its entire biosphere, how long would it take to lose its oxygen?
- Assume a world with a thick layer of frozen volatiles outside the a star’s habitable zone. Assume it is as ideal for this situation as possible. When the star enters its giant phase and the planet finds itself in the habitable zone, would there be enough time for life and oxygen to develop before the star burns out?
Again, I apologize for taking over a week to respond, but RL has been busy. Thank you for any chance you have to respond.
I have a pondering that you might be able to answer. Earth's habitability and atmosphere is due in no small part due to the magnetospheres ability to protect us from the solar winds that might strip away our atmosphere. Yes Venus has practically 0 magnetosphere but there's something else going on there that helps maintain the atmosphere.
Would a gas giant like Jupiter in orbit where we are produce a large enough magnetic shield to protect it's moons without their own magnetospheres from the solar wind and if so would it have an outer limit? IE - would a jovian planet create a habitable zone around it where moons without magnetospheres would be safe? I assume that beyond that point a moon with a terrestrial magnetosphere would be safe as well.
Conversations with my 7 year old got me wondering, he wants to be an astro-geologist today... He'll probably want to be the guy who tests bubble gum at the factory tomorrow but I'll call today a victory for science.
Derek Stanley
Sent from my iPad
> On Apr 21, 2014, at 11:26 AM, <> wrote:
>
> You, sir, are a true poet! ;) :D
>
>
> But anyway - if you can write some specific questions then I can try answering them (I'm not particularly inclined to read 75 messages to find out what they are!)
>
> Basically, we were discussing about habitable planets, how to get them, and what the stellar
> implications were. My basic position was that for a planet to have an nitrogen/oxygen
> atmosphere (i.e. atmosphere codes 2-9;D-F, or at least 4-9) requires some kind of biosphere
> that took a really, really long time to develop.
Generally this seems to be true. On Earth, oxygen didn't start building up in the atmosphere until it had essentially dissolved to capacity in the oceans and reacted with sediments and got locked up in whatever rocks it could bind with too.
> If a world had no life, the oxygen wouldn’t be in the atmosphere.
That isn't necessarily true. There is another possible way for oxygen to show up - photodissociation of water vapour in the atmosphere by solar UV radiation (UV hits H2O, H2 is lost to space, O hangs around in the atmosphere). On Earth there isn't really enough water vapour in the atmosphere for it to build up, but an panthalassic/ocean world where H2O may be a significant percentage of the atmospheric composition, it's possible that enough of it could dissociate over time to build up O2 in the atmosphere. Someone's probably done more exact calculations, but I would think you'd only get a breathable atmosphere like this in rare cases (the O2 has to dissolve in a lot more water, for one. And having that much water in the atmosphere would end up with a 'moist greenhouse39; that wouldn't exactly add to the world's habitability).
> Since that level of oxygen takes so long and takes at least some kind of life, that means
> such a planet really needs a reasonably stable star, meaning likely one of F G K M main
> sequence.
Generally, yes. Late F V to mid K V is probably best for an earthlike planet (lower mass stars would tidelock planets in their habitable zones).
> Obviously, the ancients can influence this, but there *were* only 400 of them (even if they
> controlled billions of subjects, there were only 400 of them), and even then there is only so
> much they can do over their 10,000 – 20,000 years of activity.
And even if they did anything, 300,000 years is enough time for any changes that they made to decay back to their natural state.
> - Is the above even remotely close to correct?
At least some of it is, as best we know. :)
> - Granted, we only have a sample of 1, but is it feasible for primitive life to generate an
> appreciable oxygen atmosphere over 300,000 years? Or would it take millions of years?
On a planetary scale? No way. It'd take hundreds of millions of years.
> - If a world had a type 6 atmosphere, but lost its entire biosphere, how long would it take
> to lose its oxygen?
If all life of every kind just magically keeled over and died and nothing else arose in its place? I don't know. I'm not sure what would happen to all the dead organic material of the biosphere if all the bacteria etc that caused organic matter to decay died out too. Would the oxygen in the atmosphere chemically react with it somehow? Weather presumably would still happen, so the remaining oxygen could be used up in the fires caused by lightning strikes. At a guess, I'd say... maybe a million years? Possibly less? Oxygen's a pretty reactive gas after all.
> - Assume a world with a thick layer of frozen volatiles outside the a star’s habitable zone.
> Assume it is as ideal for this situation as possible. When the star enters its giant phase and
> the planet finds itself in the habitable zone, would there be enough time for life and oxygen
> to develop before the star burns out?
If there's a few billion years of stability during a giant phase, maybe (only likely with K V stars, and even the oldest of those haven't had time since the formation of the universe to evolve off the main sequence yet). It probably won't happen during the subgiant or red giant branches, but the Horizontal branch is the most stable of the post-MS stages, so possibly then? But again, I can't see that happening for stars that are 1 solar mass or more massive.
> Would a gas giant like Jupiter in orbit where we are produce a large enough magnetic shield to protect it's
> moons without their own magnetospheres from the solar wind and if so would it have an outer limit? IE -
> would a jovian planet create a habitable zone around it where moons without magnetospheres would be
> safe? I assume that beyond that point a moon with a terrestrial magnetosphere would be safe as well.
I'd actually think it's more likely that a moon without a magnetosphere orbiting a jovian with a powerful magnetosphere is more likely to lose its atmosphere than a moon with a magnetosphere. Jupiter's magnetosphere actually traps and accelerates the solar wind particles, which then rain down on the satellites and would sputter away at their surfaces and atmospheres. I think a habitable moon would need to have a pretty strong (earth-strength) magnetic field of its own to protect against that and be able to retain its atmosphere - it'd have lots of pretty aurorae too.
So the magnetosphere acts almost like a venturi for particles… interesting. Would tidal locking to the gas giant kill off the internal dynamo or would the gravitational stresses put on the moon by the giant be enough to keep things liquid?
From: [] On Behalf Of
Sent: Tuesday, April 29, 2014 8:39 PM
To:
Subject: Re: [Traveller_TNE] Re: Plaintive Cry
> Would a gas giant like Jupiter in orbit where we are produce a large enough magnetic shield to protect it's
> moons without their own magnetospheres from the solar wind and if so would it have an outer limit? IE -
> would a jovian planet create a habitable zone around it where moons without magnetospheres would be
> safe? I assume that beyond that point a moon with a terrestrial magnetosphere would be safe as well.
I'd actually think it's more likely that a moon without a magnetosphere orbiting a jovian with a powerful magnetosphere is more likely to lose its atmosphere than a moon with a magnetosphere. Jupiter's magnetosphere actually traps and accelerates the solar wind particles, which then rain down on the satellites and would sputter away at their surfaces and atmospheres. I think a habitable moon would need to have a pretty strong (earth-strength) magnetic field of its own to protect against that and be able to retain its atmosphere - it'd have lots of pretty aurorae too.
> So the magnetosphere acts almost like a venturi for particles… interesting. Would tidal locking to the > gas giant kill off the internal dynamo or would the gravitational stresses put on the moon by the giant
> be enough to keep things liquid?
I dunno about the venturi thing... is that the same as "accelerates solar wind particles"? ;)
Tidal locking I guess would depend on the distance of the satellite from the jovian (and hence its rotation/orbital period). Magnetic fields are generated by currents of circulating conductive material in a world's interior (be that molten iron in a core or a near-surface salty ocean), and the world needs to be rotating somewhat rapidly to sustain those currents. Ganymede's magnetic field is internally generated in a molten core (and an near-surface ocean, for that matter), but it's pretty weak compared to Earth's - probably because the rotation/orbital period is about a week.
The real question is whether a satellite with the right composition and an orbital/rotation period of a day would be able to create have a field comparable to the Earth because of that. Unfortunately, while Io has a molten core and a similar rotation period, it doesn't appear to have its own magnetic field - most likely because it's so extremely heated by tidal forces that any stable circulation in its interior is impossible. So... maybe?
Which kinda answers both of your questions, I guess. Too much tidal heating is bad because it would disrupt the internal currents needed to generate the field.
So more or less for a moon of a gas giant to be habitable it's have to be a good ways out and not tidally locked. One of the best views in the galaxy and there's more working against you than for you. Suck it Ewoks!
Except for the fact that it would be tidelocked at any reasonable distance from the gas giant. Problem - to have an earth-sized moon, you need a massive gas giant (about 5-10 jupiter masses). More massive gas giants tend to have very strong magnetic fields. Strong magnetic fields close to stars (i.e. in the habitable zone) trap and accelerate lots more solar wind particles than in gas giants further away (so if Jupiter is bad, a more massive jovian closer to the star should be worse). Maybe an earth-sized rocky/metallic moon could generate a strong enough magnetic field to keep those charged particles at bay, but it's going to be a struggle.
If we put the moon further away then we have more chance of being outside the magnetic field. But there's only so far you can move the moon out before it gets into unstable orbits because the Hill Sphere (the sphere of influence) of the superjovian is going to be pretty small that close to the star. But if we can put the moon outside the jovian's magnetosphere, we run into another issue - it's still (probably) going to be tidelocked to the planet, and being further away that means that it's day (relative to the sun) is going to be more like a week or two long. Also, solar tides could mess with that (I'm not sure if they can or not - but the interplay between planetary and solar tides at that distance may mean that the moon gets into a weird resonance which could make the rotation period even longer, like one rotation every three orbits or something).
How about a gas giant like Saturn, I read there's practically no magnetosphere there but could a giant like Saturn survive in where we are?
Jupiter radiates more energy than it receives, could there be a balance point where it's far enough out where the solar particles accelerator is low enough not to fry any atmosphere but the combined heat from the gas giant and the sun would work? I mean the transit through the shadow on the dark side would be bitchingly cold but would only last a short time. Bah it'd still be tidally locked so only one side would benefit from the Jovian heat...
Derek Stanley
Sent from my iPad
> On May 3, 2014, at 11:22 PM, <> wrote:
>
> Except for the fact that it would be tidelocked at any reasonable distance from the gas giant. Problem - to have an earth-sized moon, you need a massive gas giant (about 5-10 jupiter masses). More massive gas giants tend to have very strong magnetic fields. Strong magnetic fields close to stars (i.e. in the habitable zone) trap and accelerate lots more solar wind particles than in gas giants further away (so if Jupiter is bad, a more massive jovian closer to the star should be worse). Maybe an earth-sized rocky/metallic moon could generate a strong enough magnetic field to keep those charged particles at bay, but it's going to be a struggle.
>
> If we put the moon further away then we have more chance of being outside the magnetic field. But there's only so far you can move the moon out before it gets into unstable orbits because the Hill Sphere (the sphere of influence) of the superjovian is going to be pretty small that close to the star. But i f we can put the moon outside the jovian's magnetosphere, we run into another issue - it's still (probably) going to be tidelocked to the planet, and being further away that means that it's day (relative to the sun) is going to be more like a week or two long. Also, solar tides could mess with that (I'm not sure if they can or not - but the interplay between planetary and solar tides at that distance may mean that the moon gets into a weird resonance which could make the rotation period even longer, like one rotation every three orbits or something).
>
>
> So the upshot is... it's pretty complicated ;).
>
Saturn does have a magnetic field - one of the reasons that Titan can keep its atmosphere is because it (mostly) orbits outside it.
Jupiter is nowhere near massive enough to heat its satellites (beyond a few millions years after its formation). But even superjovians and brown dwarfs won't cut it - they cool too quickly. Massive brown dwarfs might stay warm enough for a couple of billion years but after that any moon in its habitable zone would freeze.
One question occurred to me: how dependent is a gas giant's radiation belt on solar/stellar wind? Could they be reduced in cooler stars so that GG satellites could retain atmospheres?
Eamon
--------------------------------------------
On Wed, 30/4/14, <> wrote:
Subject: Re: [Traveller_TNE] Re: Plaintive Cry
To:
Date: Wednesday, 30 April, 2014, 4:39
> Would
a gas giant like Jupiter in orbit where we are produce a
large enough magnetic shield to protect it's > moons without their own
magnetospheres from the solar wind and if so would it have
an outer limit? IE - > would a jovian planet create a habitable zone
around it where moons without magnetospheres would
be > safe? I
assume that beyond that point a moon with a terrestrial
magnetosphere would be safe as well.
I'd actually think it's more
likely that a moon without a magnetosphere orbiting a jovian
with a powerful magnetosphere is more likely to lose its
atmosphere than a moon with a magnetosphere. Jupiter's
magnetosphere actually traps and accelerates the solar wind
particles, which then rain down on the satellites and would
sputter away at their surfaces and atmospheres. I think a
habitable moon would need to have a pretty
strong (earth-strength) magnetic field of its own to
protect against that and be able to retain its atmosphere -
it'd have lots of pretty aurorae
too.
As I understand it, the radiation belts are pretty much entirely dependent on the solar wind. If the jovian is closer to the star then there will be a lot more radiation because the wind will be stronger (due to the inverse square law). Cool stars will have habitable zones that are much closer than warmer stars, so if anything the problem could be even worse there.
If the jovian had a weaker/smaller magnetic field then that would offset the problem somewhat.
A quick resurrection of this old thread with a few questions:
If the Gas Giant's orbit was inclined to the solar equator, would its exposure to the maximum solar wind strength be reduced enough to have an effect on its radiation belts?
Are there any theories on the rate of decay of a Gas Giant's magnetic field? Is it plausible for one to lose enough strength over a reasonable time (i.e. well before the central star enters the twilight years of its life)?
On a different note, mega-earth or gas dwarf exoplanets could be substituted for gas giants for traditional Traveller inhabitable gas giant moon situations.
Eamon
--------------------------------------------
On Fri, 16/5/14, [Traveller_TNE] <> wrote:
Subject: Re: [Traveller_TNE] Re: Plaintive Cry
To:
Date: Friday, 16 May, 2014, 15:58
As I understand it, the radiation belts are pretty
much entirely dependent on the solar wind. If the jovian is
closer to the star then there will be a lot more radiation
because the wind will be stronger (due to the inverse square
law). Cool stars will have habitable zones that are much
closer than warmer stars, so if anything the problem could
be even worse there.
If
the jovian had a weaker/smaller magnetic field then that
would offset the problem somewhat.
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1) It's probably not going to be possible to have its orbit inclined to such an extent to make any difference. I think the solar wind is generally constant regardless of orbital inclination.
2) Again, probably not. There's a lot of stuff inside a gas giant, enough to drive convection currents in its conducting interior for billions of years. It may lose a bit of strength but I'd guess that most jovian fields would survive to the end of the star's life. The fields of rocky planets however might not (Mars' field is already dead, Earth's would probably last at least a couple more billion years, and Venus' might actually *start up* in a few billion years time as it cools down enough to start compositional convection in its core).
Isn't the assumption with mars that the magnetic field was largely done in by the impact the blew the top half of the planet off? It's been a while since I read that so it's probably changed now, but I thing the though is that impact is probably what lead to the rapid decline of Mars' internal dynamo.
Derek Stanley
Sent from my iPad
> On Aug 29, 2014, at 10:36 PM, " [Traveller_TNE]" <> wrote:
>
> 1) It's probably not going to be possible to have its orbit inclined to such an extent to make any difference. I think the solar wind is generally constant regardless of orbital inclination.
>
>
> 2) Again, probably not. There's a lot of stuff inside a gas giant, enough to drive convection currents in its conducting interior for billions of years. It may lose a bit of strength but I'd guess that most jovian fields would survive to the end of the star's life. The fields of rocky planets however might not (Mars' field is already dead, Earth's would probably last at least a couple more billion years, and Venus' might actually *start up* in a few billion years time as it cools down enough to start compositional convection in its core).
>
Sort of. This explains it pretty well (I didn't know about the idea that Mars could actually generate half a magnetic field - apparently this could be due to a giant impact in the north so you're partly right). http://www.planetary.org/blogs/emily-lakdawalla/2008/1710.html http://www.planetary.org/blogs/emily-lakdawalla/2008/1710.html
I was thinking that perhaps because planetary magnetospheres were a bit squashed, that the solar wind might be constrained by a similar magnetosphere.
Sent from my iPad
On 30 Aug 2014, at 14:36, " [Traveller_TNE]" <> wrote:
> 1) It's probably not going to be possible to have its orbit inclined to such an extent to make any difference. I think the solar wind is generally constant regardless of orbital inclination.
>
>
> 2) Again, probably not. There's a lot of stuff inside a gas giant, enough to drive convection currents in its conducting interior for billions of years. It may lose a bit of strength but I'd guess that most jovian fields would survive to the end of the star's life. The fields of rocky planets however might not (Mars' field is already dead, Earth's would probably last at least a couple more billion years, and Venus' might actually *start up* in a few billion years time as it cools down enough to start compositional convection in its core).
>
That would explain why by the 57th century, Mars still doesn't have a nice breathable, but thin (5) atmosphere, some hydrographic coverage, and at least some significant oasis settlements. The "greening" of Mars would likely take some significant alterations on a planetary scale to its magnetic fields, else you are fighting a losing battle trying to thicken up its atmosphere in preparation for additional terraforming.