Is Saturn a failed gas giant? | Hacker News Reader

Is Saturn a failed gas giant?

arxiv.org

59 pointslooperhacks58 comments

TIL that Uranus and Neptune fall into a different category than Jupiter and Saturn (ice giants vs. gas giants - https://en.wikipedia.org/wiki/Giant_planet).

I learned about the term Jovian from "We Are Legion (We Are Bob)" The idea of somehow capturing ice giants and bringin them into the zone where they would melt to create water in the planets closer to the star is a stelar system is fascinating.

Also: the solar system would look completely different if Jupiter was not a thing.

The Sun is 99.9% of the mass in our solar system. Jupiter is most of the remaining 0.1% and then the rest of the planets are included in the 0.01%.

Also, Jupiter is the only planet that orbits around a point outside of the surface of the Sun. All the other planets point of orbit are below the surface of the Sun.

Jupiter is massive.

> Also, Jupiter is the only planet that orbits around a point outside of the surface of the Sun.

Put differently, Jupiter and the Sun orbit one another.

Every two body orbit involves a barycenter that is not exactly in the center of either body (i.e. every planet/sun combo "orbit around one another").

The unique aspect of Jupiter is that the Jupiter/Sun barycenter is outside of the surface of the Sun. This requires an incredible amount of mass in Jupiter.

For the same reason that we demoted Pluto to dwarf-planet status, I'm fully prepared to elevate Jupiter to super-planet status for this fact alone.

What if we demote the sun? It is in a class of stars that is too small to have a internal barycenter for all it's planets, there are larger stars that do because planets like Jupiter have a limit before they start being classed as Brown Dwarfs.

The sun is a pretty ordinary star. It's not nearly so small that it should be demoted or we would be rewriting our entire stellar classification system.

74% (don't quote me here, this is from memory) of stars are less massive red dwarfs. Only about 4% (again don't quote) stars fall into our weight class.

Yes but I mean our sun is not at the low end of that spectrum. As you say, most stars are smaller than the sun. So rewriting the system would mean that the majority of stars are no longer stars.

The sun is actually fairly unusual for a star. Most stars are smaller than the sun.

Sure, greater-than-dwarf-sized stars are actually the minority. But among greater-than-dwarf-sized stars the sun is fairly typical.

And more variable than the Sun.

We're not just rewriting the system for the sun though. There have to be many stars that aren't large enough to have internal barycenters for all their planets. Maybe we do want to define the stars that have this trait and not the planets in their solar systems.

Would the category of "mid-size star with a large planet" be useful?

Maybe if it is predictive of having earth-like planets in the habitable zone...

> What if we demote the sun?

You mean, make it a “dwarf star”?

It... already is.

Would a small enough celestial object orbiting the sun have a barycenter that is effectively the center of the sun? How small would it need to be?

Sure, just depends on your definition of "effectively" if that's a pea or a moon?

How close is "effectively"?

Within the radius of the smaller body within the larger body.

I'll go with that answer.

https://spaceplace.nasa.gov/barycenter/en/

And https://en.wikiversity.org/wiki/Solar_System,_technical/Sun#... has the location of the barycenter of the solar system for a number of years.

There's a lightbulb & Princeton grad joke in there somewhere.

99.89%?

Your right, I can't mass

The fun thing is that Jupiter was migrating into the inner solar system and Saturn managed to convince it that it would be a bad time so they migrated back out. It's fascinating. I didn't realize the term ice giant was so unknown. It's a sample of one thread but I'd bet that if I asked a lot of my friends and family they wouldn't know it either.

Saturn paid attention to mortgage rates while Jupiter was just going to buy whatever the missus wanted to keep her happy.

Sounds like a great thing — until the orbits of the rest of the planets destabilize and Earth gets ejected from the solar system.

'Tho if we have the technology and energy to move gas giants into different orbits, we probably have the capacity to actively keep Earth in a proper orbit (and imparting that much energy into the crust might make some interesting phenomena)

The context was for terraforming other systems. One would hope we would not pull this stunt back home. Apparently jovians are a thing and it is considered (at least in scifi - haha) as an option.

+1 on we would need to have the tech to do it.

Even if you somehow managed to move a gas giant around, what would you do with it once you relocated it? It's a big well of gravity leading to a hot, fast death with nothing to stand on.

Floating cities should be possible given the density of the atmosphere. Not sure Jupiter's atmosphere is stable enough though. Might be like living on a raft in a hurricane.

That the atmosphere is mostly hydrogen doesn't make for easy ballooning. There isn't really a gas much lighter to provide lift. It also begs the question of 'why'. Everywhere you look, there is only wind, and no minerals to repair things with.

A giant platform, with tubes hanging down to mine hydrogen and be a space gas station, partly fusioning it for energy and thrust to propel and keep it up, something like that?

Any of the gas they 'mined' (ignoring the immense difficulties of trying to mine liquid hydrogen) would be stuck on the platform without a rocket to carry it out of orbit. It would be much, much easier to stick a base on Ganymede or something and convert some of the ice there into fuel.

Difficulties? I thought liquid, so just suck it up? And with "gas station" I meant ships coming by and fetching it, so there is your rocket :D Ok, thinking too much the space trucker way, but isn't water much less of a fuel than hydrogen?

Hydrogen only exists as a liquid at very uncomfortable pressures and temperatures.

Water can be split into its separate components. It's much easier to gather water than it is liquid Hydrogen, and if one wanted to make a gas station, it would make sense to build it on an asteroid or a small moon where takeoff and landing uses little fuel. Not on a gas giant with triple digit escape velocity and a thick atmosphere asking for a massive heat shield.

Location, location, location. Ceres, that's where you want to set up. Just enough gravity so you probably can't jump off it, lots of ice, a fair bit closer than Ganymede with easier take offs, convenient halfway between Mars and all those Jovian moons. Open 24/7 and sell the hot dogs at cost.

For that energy budget it’s probably easier to bring your own phobos-sized body and pepper it with minerals mined nearby.

Earth would look different too. Through its' high mass, Jupiter gets the most visits by asteroids. He protects us. The romans named their highest god Jupiter.

One thing I'm pretty confident humanity will never do is move planets around like marbles. The masses involved make the suggestion laughable.

There’s a British space comedy called Red Dwarf that has surprisingly good novelisations by the original show writers. One novel has a sequence where they play pool with planets, obviously completely unrealistic but it’s a really fun sequence.

There’s also another separate sequence describing how humans abandon Earth and use it as a giant landfill, resulting in a massive methane explosion that shoots Earth out of the solar system and into frozen deep space. All very silly but very imaginative.

It's a pretty dangerous game to play in any case. One slight deviation in a planet's orbit can throw an entire solar system out of balance over not-so-long time periods. Before you know it, your lush green planet is hurtling out alone into interstellar space, dooming your civilization to a quick death on an icy rogue world.

Sounds like the kind of thing an "enlightened" trillionaire might try. See also, geoengineering..

I feel like this thread is writing the next great Jerry Bruckheimer or Micheal Bay movie.

Larry Niven's "A World Out of Time" had this as a plot device, when he wrote it in the 70s. I enjoyed the book a lot, a lot of hard-sci-fi readers did not.

Don't worry about those haters with papers. You haven't failed. Just keep on being Saturn.

https://en.wikipedia.org/wiki/Gas_giant:

> However, in the 1990s, it became known that Uranus and Neptune are really a distinct class of giant planets, being composed mainly of heavier volatile substances (which are referred to as "ices"). For this reason, Uranus and Neptune are now often classified in the separate category of ice giants.[2]

I guess there's a distinction I wasn't aware of.

Edit: I had this comment written, but I guess I waited too long to submit.

> heavier volatile substances (which are referred to as "ices")

When you know that astronomers call about anything that is not hydrogen or helium "metals" and you learn that even gazes are "ices" for some reason¸ makes you think now would be a good time to level the playground and start again :)

I agree, but from what I understand it's partially about things typically behave. At super cool temperatures, ice acts like stone, and a bunch of other stuff will appear to be as strong as metals. There's also a ton of tradition dating back to the renaissance time period.

Rocks are basically silicon ice.

It's all about finding ice XI.

The abstract (all I read) doesn't explain why Saturn is a failed gas giant. I thought it was considered simply a gas giant?

Are we cancelling Saturn now?

Seems pretty giant to me.

Yeah, that's pretty rich coming from researchers who are 25 orders of magnitude smaller.

Saturn still emits more heat than it receives from the present sun.

As opposed to its previous star?

Old Hebrew word for sun is Shamash. Tablets of Shamash give a hint.

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