Saturn's Interior After the Cassini Grand Finale
arxiv.org
arxiv.org
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)
Is there a term that describes the sort of oscillation you're talking about, by the way? Wherein object A is embedded 'within' object B?
> 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.
[1] https://en.m.wikipedia.org/wiki/Fluid–structure_interaction
- Moving Carl Sagan's Voice - deepfake audio synthesis
- Stunning visuals - Generative AI trained on NASA archives and sci-fi movie footage
- Awe-Inspiring Narrative - GPT trained on Sagan, Ray Bradbury, etc
Once we are there -- I wonder what becomes the new frontier for creative output that makes us say "AI cannot do THIS -- it takes a human"
https://www.pbs.org/video/cassini-spacecraft-final-moments/
which is in general full of some pretty excellent simulations, arranged very aesthetically
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.
I suppose it means the boundary is a massive and eternal dust storm. That's the only way I imagine solids and gases to "mix".
> 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.
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.
For example, shifting the band of tolerance for gravity, temperature, gas pressure, etc.
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.
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.
1. https://en.wikipedia.org/wiki/Interplanetary_Transport_Netwo... 2. https://www.smithsonianmag.com/air-space-magazine/cubesat-at...
Arthur C. Clarke - A Meeting with Medusa
Robert L. Forward - Saturn Rukh
Michael McCollum - The Clouds of Saturn
Ben Bova - Leviathans of Jupiter
And an honorable mention to Carl Sagan - Cosmos : One Voice in the Cosmic Fugue https://vimeo.com/284643737
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.
That collection also has uplifted dogs and ants.
Frederick Pohl (another SciFi Grandmaster) tackled the Mars issue in ManPlus
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.
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.
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.
Cheap orbital access will hopefully give us a lot more science missions.
Yes, I know there are a million reasons that it won't work but still...
I guess 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.
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.
Instead they speak about a mixed core extending to half the radius.
Can anyone explain what differential rotation means, with reference to the harmonics listed in the paper? Thank you!
I now know why, lol.