The part about Saturn’s deep rotation is very interesting. Voyager in the 80s measured Saturn’s rotation (based on radio signals) at 10h39m, while Cassini itself before the Grand Finale measured Saturn’s rotation (again based on radio signals) at 10h45m. Now with the Grand Finale data, Cassini has measured the “deep” (core) rotation at 10h33m.
All the measurements are regarded as correct. The explanation for the 6 minute disagreement between Cassini in 2004-05 (10h45m) and Voyager in 1980-81 (10h39m) was proposed to be slippage between Saturn’s magnetic field and Saturn’s core causing the magnetic field to be slowing down (and presumably speeding up) over time. The explanation for the difference between Cassini’s radio measurements of magnetic field rotation (10h45m) and Cassini’s Grand Finale measurements of core rotation (10h33m) is that Saturn likely has pretty extreme differential rotation: the core rotates once every 10 hours and 33 minutes, and the concentric layers of its atmosphere rotate progressively slower.
I’m guessing the core is throwing out a steady magnetic field but there is enough magnetically charged material in the slower-rotating layers to drag on that magnetic field. Likely that there’s some grand cycle going on: as the magnetic field rotation is slowed by charged atmosphere drag, the core begins to exert more force on the atmosphere through magnetism in addition to friction, speeding the atmosphere’s rotation back up. Because of the massive amounts of material involved, there is a massive amount of inertia, and the system overshoots equilibrium. It’s getting very speculative and well outside my layman’s expertise but I think this would predict there are periods during the cycle where the atmosphere of Saturn actually rotates faster than the core does! I think it’s also possible that the cycle goes from “significantly slower than core” to “slightly slower than core” and back?
At this point I am well into fantastical sci-fi scenarios but I can also imagine the differential rotation being too strongly determined by friction and other non-magnetic forces, so all of this charged drag is concentrating certain types of material (highly affected by the magnetic field, relatively free to move) into a thin shell some distance from the core, and that shell expands and contracts in diameter as it tries to find the specific height in the atmosphere that is currently rotating at the same speed as the magnetic field is. So like a marble inside a balloon, and the balloon is expanding and contracting, except there’s a bunch of gas inside and outside the balloon obscuring all of this from our sight.
I don’t know of a good term, no. “Differential rotation” is the broader concept but almost all of the information there is about bodies of fluids, with not much treatment of discrete objects. Even a single discrete object inside a body of fluid is hard to find information on; “object A inside shell B, all in a fluid C” is probably asking too much. Hopefully someone does, though! This is probably one of those cases where if you know the right term you can access a whole hidden field of literature on the topic.
Would fluid-structure interaction [1] with encapsulated systems fit the bill? It’s a subset of continuum mechanics which is probably the best field to model the layers of atmosphere as a mix of solid and fluid continuums and oscillatory systems are a defining feature of the field:
> Fluid–structure interaction (FSI) is the interaction of some movable or deformable structure with an internal or surrounding fluid flow. Fluid–structure interactions can be stable or oscillatory. In oscillatory interactions, the strain induced in the solid structure causes it to move such that the source of strain is reduced, and the structure returns to its former state only for the process to repeat.
IANAAstrophysicist, but I'm pretty sure that, with no external driving force, such an oscillation in differential rotation rates would die out quite quickly.
I would have thought so too, but losing 6 minutes out of 10.5 hours in just 25 years is a pretty major change on the timescales that planets operate on.
If someone could get high quality stuff from all these tools, combine it well, and compose the whole video to a similar quality, I would say they would be equally talented. Even if they spent a fraction of the time on it.
I kind of like the idea that these gas giants have more rocky planet mass in their cores than all the rocky planets in the solar system combined.
Hard to tell, this paper describes the core as mixed with the gases and in fact it may extend out to 1/2 the planet's radius in a fuzzy sort of way.
So these cores are not like massive Earths sitting inside with clearly defined boundaries but rather various gradients with fuzzy boundaries as they mix into the rest of the plant's atmosphere.
I wonder if Jupiter's core has a similar structure.
Yes, based on Juno’s observations it has become more likely that Jupiter’s core is also "fuzzy", having been slowly dissolving into the surrounding metallic hydrogen sea since the planet’s formation and may even have completely dissolved and mixed by now.
Jupiter and Saturn have swallowed a mind-boggling amount of rocky and metallic meteors. They have to go somewhere, and it's unlikely they're just dissolved into the atmosphere. They'll sink to the core and join the others, so there must be some amount of molten rock and metal at the core, negligible to the size of thse planets yet massive compared to the amount that has fallen to Earth.
You seem to be speculating based on unfounded assumptions. Luckily we don't have to assume or speculate, because we know quite a bit about the interior of the giant planets these days.
> a mind-boggling amount of rocky and metallic meteors.
With a total mass a mind-bogglingly tiny fraction of their original rocky-icy cores. Just like with Earth, any post-formation mass increase is a rounding error of a rounding error, because by definition the era of planet formation stopped when the planets ran out of raw material to capture!
> They have to go somewhere, and it's unlikely they're just dissolved into the atmosphere.
Unlikely by what argument? Essentially anything that falls into one of the giant planets is vaporized high in the atmosphere, long before even hitting the cloud tops! Some of the gaseous meteor stuff may recondense into microscopic dust particles that will remain in the atmosphere due to buoyancy and other forces that vastly exceed gravity at those scales.
Any hypothetical chunk of solid matter that somehow falls through the upper atmosphere and the cloud layers intact will encounter a layer of hot supercritical fluid at tremendous pressures, thousands of km thick, and get quickly dissolved.
And below the supercritical fluid there's an even more exotic mantle that comprises around 75% of the total mass of the planet and most of its volume. The mantle is made of extremely hot, extremely reactive, exotic liquid metallic hydrogen on observations of the giant planets' magnetic fields. There's absolutely nothing that can fall through that intact even in theory.
> So there must be some amount of molten rock and metal at the core
No molten rock or metal can exist in the core due to the pressure. However, as I said, there are definitely several Earth masses worth of silicates, and some but not much metal, in the core, because that's the original core that formed first and started attracting gas. Again, the question is whether at least some of that material forms a well-defined solid core, or whether all of it has been dissolved away by the metallic hydrogen mantle surrounding it. The best current models indicate that there's no well-defined boundary and the entire core is "fuzzy" and mixed with the mantle.
It's rocky in the sense that it has elements heavier than hydrogen and helium, but not in the sense that it's solid. Temperature within the cores reaches 40k Celsius, so everything is molten.
At the pressures and temperatures we’re not talking about either gases or liquids but a supercritical fluid and even more exotic phases, including liquid metallic hydrogen which is thought to be an excellent solvent.
If you want to learn more about the Cassini mission and also learn SQL, there is the fantastic book called "A curious Moon". Which teaches SQL with the original Cassini/Huygens data from the Enceladus flyby.
There are conditions where humans just cannot perceive what is going on.
There's a story from (I just looked it up) 1944, before it was widely known the gas giants have no surfaces, about humans who modify themselves to explore Jupiter.
Before the characters undergo the transformation, they see Jupiter as a terrifying wasteland of never-ending storms - and after, nobody comes back.
If I remember correctly, the story is about a man and his dog who go through the process and then, when it is complete, Jupiter appears as a paradise and they realize that the reason people don't come back is because it's a better life once they become Jovians.
“Four men, two by two, had gone into the howling maelstrom that was Jupiter and had not returned. They had walked into the keening gale – or rather, they had loped, bellies low against the ground, wet sides gleaming in the rain.
For they did not go in the shape of men.”
The end is:
"'They would turn me back into a dog,' said Towser.
'And me,' said Fowler, 'back into a man.'"
I hadn't realized how much that story affected me, because my reaction to colonizing Mars, for years, really, has been that it's pointless to try until it's practical to become Martians. Otherwise you might as well live in a cave anywhere. But I didn't link it consciously.
I believe somewhere in the Culture series books it is mentioned that many Culture ships also have gas dwellers as inhabitants. By neccesity in separate compartment from the usual terestrial-lineage passengers. I like to believe that alongside all the fractal complexity of Culture life depicted in the books they also have a paralel world with even more exotics. Maybe there is a gas-dweller equivalent of Contact going around Jovians galaxywide getting into all kind of schenanigans.
Yes. That is true. But I meant a smaller part. In Excession this part about the avatar of GSV Sleeper Service as it is contemplating offloading all of its cargo: "There was an extra, perhaps deeper melancholy at the thought that it would no longer be able to play host to the living things aboard; the creatures of the sea and the air and the gas-giant atmosphere, and the woman."
Previously in the same book it is implied that these "creatures of the gas-giant atmosphere" are animal level intellects. But my headcanon is that perhaps there are Culture ships with Nasqueron Dwellers or similar intelligent gas-dwellers with complex societies on-board.
You are absolutely right that The Algebraist is full of gas-dwelling creatures. But as far as I can recall while they have a "Culture" feel to them there are no direct Culture references in that book. But maybe I have missed something.
Simak included dogs in his stories so often (and especially in that anthology you mentioned) that any time someone mentions a sci fi story with a dog, my first thought is that it has to be a Simak story. :)
I've thought for a long time that the only way to colonize the solar system would be to genetically adapt humans to the conditions. They'd still need life support, but not as much.
For example, shifting the band of tolerance for gravity, temperature, gas pressure, etc.
I've had sort of the opposite thought (not that there's anything resembling a singular "right answer" on topics like this): we shouldn't try to colonize Mars until after we've terraformed it.
Scientific outposts would be fine, but much like Antarctica, no one ought to be in a position where they have to live in caves or cans their entire life.
> Scientific outposts would be fine, but much like Antarctica, no one ought to be in a position where they have to live in caves or cans their entire life
Kim Stanley Robinson’s Mars trilogy changed my mind on this. There is natural beauty there that is worth trying to preserve and experience. Yes, we should terraform. But slowly and deliberately. A good way to check this is to have humans on the surface while terraforming takes place.
My concern is that humans "on the surface" (really, in habitats) are going to live pretty miserable lives for a really long time.
Compare Mars to Antarctica. While there's a significant science-focused presence, no one lives there lives there. While various treaties complicate the issue, to the best of my knowledge, no one even speaks about wanting to spend their entire life there. Living permanently on Mars without extensive terraforming would mean generations of people living out their lives in caves and metal cans, never getting to go outside without putting on the equivalent of a SCUBA suit, at a minimum. It makes for great stories, but as a cradle-to-grave life is seems unethical to help create that situation.
Besides, I think gradual (or no) terraforming of Mars is doomed. Getting to orbit is increasingly cheap, and that makes getting to Mars easier, whether by the ITN [1], or more direct method. You can get to Mars with a Cubesat-type spacecraft design. [2] Somebody is going to leverage those possibility to start terraforming Mars, if they haven't done so already. Optimal terraforming probably requires adding atmosphere, presumably via comet impacts. That will take more than Cubesats, but the possibility was demonstrated by DART. Unless our civilization collapses, fast terraforming of Mars is only going to get easier, and probably sooner rather than later, someone will start the process.
Is it really possible to contain the terraforming? Even if you have domes, it seems like it's only a matter of time before single celled organisms escape and find a way to survive, and then begin to alter the environment.
> it's pointless to try until it's practical to become Martians.
We'll need to shed these bodies evolved for earth gasses, gravity, nutrients, temperatures, and radiation environment.
Brain uploads to computers would let us go anywhere. Or perhaps more probably, AI will take over evolution in our stead. No human body and death to disadvantage them.
I’ve outlived every computer I know of and I’m not even that old. How do AI people think AI will live so long without being unplugged, losing a power source, or having errors? In a future without humans I mean. We are the universal troubleshooting organism.
In one lifetime you've seen computers jump dramatically in power. By the end of your life, I suspect that you'll see computers that may scare you.
But to answer your question, it's the digital data and files to look to, not the hardware. We have files floating around from the 60's today, and we're picking up more and more fidelity with which we can represent the world every year. That won't stop.
I think each layer of the interior atmosphere of a gas giant is composed differently - like, it’s not as simple as “the hydrogen layer floats on top of the helium layer”, but that gives the general idea, right?
If you find some way of shining a light or radio wave that passes through one layer and reflects off the next, you could map that boundary. I can only imagine the turbulent boundary between the two layers being one of the most beautiful sights imaginable. Endless noise on a cosmic scale, patterned first by fluid dynamics, then successively by other phenomena of physics.
As a one-time chemist, I look at the magnetic fields and abundant hydrogen and wonder if there's any way to do magnetic resonance measurements at the planetary scale to look at the innards of a Saturn or a Jupiter.
Yes, I know there are a million reasons that it won't work but still...
Saturn's equatorial radius is 60,268km, and its polar radius is 54,364km -- nearly 10% smaller.
The equatorial radius would have been smaller without the rapid rotation, and the polar radius larger, so at least we have lower and upper limits as to the size of a non-rotating Saturn.
Getting a more accurate estimate would require calculating the effect of gravity vs. centrifugal force on the density of the various gaseous layers. As long as you limit the calculation to the current state of Saturn (as if it had just stopped) and not try to extrapolate over its entire age of 4.6B years, the result is unlikely to be more than a couple of percentage points different from the current average radius.
> the solution would require a comparison to a hypothetical Saturn that has no rotation. If that's even possible.
Possible. But not probable. For one, you’d need a complete cancellation of angular momentum during formation, which is unlikely. Also, without a dynamo, even at that distance from the sun, the lighter gases would wash away.
All the measurements are regarded as correct. The explanation for the 6 minute disagreement between Cassini in 2004-05 (10h45m) and Voyager in 1980-81 (10h39m) was proposed to be slippage between Saturn’s magnetic field and Saturn’s core causing the magnetic field to be slowing down (and presumably speeding up) over time. The explanation for the difference between Cassini’s radio measurements of magnetic field rotation (10h45m) and Cassini’s Grand Finale measurements of core rotation (10h33m) is that Saturn likely has pretty extreme differential rotation: the core rotates once every 10 hours and 33 minutes, and the concentric layers of its atmosphere rotate progressively slower.
I’m guessing the core is throwing out a steady magnetic field but there is enough magnetically charged material in the slower-rotating layers to drag on that magnetic field. Likely that there’s some grand cycle going on: as the magnetic field rotation is slowed by charged atmosphere drag, the core begins to exert more force on the atmosphere through magnetism in addition to friction, speeding the atmosphere’s rotation back up. Because of the massive amounts of material involved, there is a massive amount of inertia, and the system overshoots equilibrium. It’s getting very speculative and well outside my layman’s expertise but I think this would predict there are periods during the cycle where the atmosphere of Saturn actually rotates faster than the core does! I think it’s also possible that the cycle goes from “significantly slower than core” to “slightly slower than core” and back?
At this point I am well into fantastical sci-fi scenarios but I can also imagine the differential rotation being too strongly determined by friction and other non-magnetic forces, so all of this charged drag is concentrating certain types of material (highly affected by the magnetic field, relatively free to move) into a thin shell some distance from the core, and that shell expands and contracts in diameter as it tries to find the specific height in the atmosphere that is currently rotating at the same speed as the magnetic field is. So like a marble inside a balloon, and the balloon is expanding and contracting, except there’s a bunch of gas inside and outside the balloon obscuring all of this from our sight.
(Would love astrophysicists to chime in)