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Jupiter was formerly twice its current size, had a much stronger magnetic field

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Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#11

Post by skywhopper »

HappMacDonald wrote: post #9
lazide wrote: post #4

Earlier quoted context omitted.

It was hotter, a lot hotter. Like stars, radius for a gas giant is increased by heat, and decreased by increased mass. These two factors are rarely completely independent, of course, so it gets complicated. Especially in a star where masses are large enough to result in densities sufficient to cause fusion - and large releases of heat, which then cause decreased density, etc. But all other factors being constant, the…

> Like stars, radius for a gas giant is [..] decreased by increased mass. If this is the case then do you have any intel on why do the gas giants in our system appear to more closely directly correlate mass with radius instead of inversely? https://nssdc.gsfc.nasa.gov/planetary/factsheet/ Mass: Jupiter = 3.3 x Saturn = 22 x Uranus = 19 x Neptune Radius: Jupiter = 1.2 x Saturn = 3 x Uranus = 3 x Neptune I mean Saturn'…

They’re all made out of different mixes of gases and other elements, and are different distances from the sun, and any number of other variables.

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#12

Post by raattgift »

HappMacDonald wrote: post #9
lazide wrote: post #4

Earlier quoted context omitted.

It was hotter, a lot hotter. Like stars, radius for a gas giant is increased by heat, and decreased by increased mass. These two factors are rarely completely independent, of course, so it gets complicated. Especially in a star where masses are large enough to result in densities sufficient to cause fusion - and large releases of heat, which then cause decreased density, etc. But all other factors being constant, the…

> Like stars, radius for a gas giant is [..] decreased by increased mass. If this is the case then do you have any intel on why do the gas giants in our system appear to more closely directly correlate mass with radius instead of inversely? https://nssdc.gsfc.nasa.gov/planetary/factsheet/ Mass: Jupiter = 3.3 x Saturn = 22 x Uranus = 19 x Neptune Radius: Jupiter = 1.2 x Saturn = 3 x Uranus = 3 x Neptune I mean Saturn'…

Neither Jupiter nor Saturn is close to thermal equilibrium, whereas the sun is. Bounded self-gravitating gas spheres in thermodynamic equilibrium can show negative specific heats [The classic LBLB, Lynden-Bell & Lynden-Bell, 1977 https://adsabs.harvard.edu/full/1977MNRAS.181..405L>]. A negative specific heat capacity reducews the gas's volume as its temperature increases. Temperature in stars and gas giants is mostly lowering due to outward radiation driven by internal processes. Unlike a star, Jupiter's specific heat capacity is positive. Very roughly the sun's excess power output will cause it to grow (this handwaves a complex balance of temperature, pressure, mass, and nuclear fusion as it rises in the main-sequence part of the H-R diagram https://chandra.harvard.edu/graphics/edu/formal/variable_sta...> -- as it climbs in that region with similar temperature the sun gets brighter because it gets bigger), while Jupiter's power output has been higher (presently about 2.5x) than its solar radiation input yet the planet has probably been shrinking.

The energy input and internal heat budgets are under active study for Jupiter https://www.nature.com/articles/s41467-018-06107-2> (open access), and will supply further evidence for various hypotheses about "primordial Jupiter", one of which is the topic here. One of the major points of comparison with a star here would be how the former is much more like an ideal blackbody than our local gas giants. And of course there is a dark side of Jupiter, while there is no dark side of the sun.

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#13

Post by Maxatar »

est31 wrote: post #10

How is the size defined for a gas planet? The gas density just keeps dropping, where do you draw the line (isosurface, rather)? Earth's radius is always the one without earth's atmosphere.

It's defined as the distance from the center of mass to the point where the pressure is equal to the pressure on Earth at sea level.

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#14

Post by amelius »

est31 wrote: post #10

How is the size defined for a gas planet? The gas density just keeps dropping, where do you draw the line (isosurface, rather)? Earth's radius is always the one without earth's atmosphere.

It's a matter of definitions, so we skip them and just choose something that makes sense to humans.

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#15

Post by greggsy »

lazide wrote: post #4
rwmj wrote: post #2

Couldn't read the actual paper as it is paywalled, but does "twice its current radius" mean that it had a larger mass, and if so what happened to all that extra mass?

It was hotter, a lot hotter. Like stars, radius for a gas giant is increased by heat, and decreased by increased mass. These two factors are rarely completely independent, of course, so it gets complicated. Especially in a star where masses are large enough to result in densities sufficient to cause fusion - and large releases of heat, which then cause decreased density, etc. But all other factors being constant, the…

Could it cool and crystallise?

Could those crystals then erode and reform again as sedimentary rocks to be come a solid planets like earyh?

I understand that’s not how earth itself came to be, but it’s an interesting metamorphosis that I hadn’t previously considered.

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#16

Post by jessriedel »

est31 wrote: post #10

How is the size defined for a gas planet? The gas density just keeps dropping, where do you draw the line (isosurface, rather)? Earth's radius is always the one without earth's atmosphere.

As others note, the definition of Jupiter’s radius is set by where the pressure is 1 bar. This is somewhat arbitrary, but the arbitrariness doesn’t matter much: the pressure drops to 1 microbar just 320 km higher, which is <0.5% of Jupiter’s ~70,000 km radius.

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#17

Post by jessriedel »

greggsy wrote: post #15
lazide wrote: post #4

Earlier quoted context omitted.

It was hotter, a lot hotter. Like stars, radius for a gas giant is increased by heat, and decreased by increased mass. These two factors are rarely completely independent, of course, so it gets complicated. Especially in a star where masses are large enough to result in densities sufficient to cause fusion - and large releases of heat, which then cause decreased density, etc. But all other factors being constant, the…

Could it cool and crystallise? Could those crystals then erode and reform again as sedimentary rocks to be come a solid planets like earyh? I understand that’s not how earth itself came to be, but it’s an interesting metamorphosis that I hadn’t previously considered.

Like the interior of the planet, the atmosphere is overwhelmingly hydrogen and helium. And helium is liquid even at 0 temperature unless under pressure, so presumably (?) would be liquid on the surface. These materials are mechanically very different than the silcates and metals dominating the Earth’s crust, and I don’t think we even have well measured bulk properties? Not sure what erosion processes would look like.

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#18

Post by lazide »

greggsy wrote: post #15
lazide wrote: post #4

Earlier quoted context omitted.

It was hotter, a lot hotter. Like stars, radius for a gas giant is increased by heat, and decreased by increased mass. These two factors are rarely completely independent, of course, so it gets complicated. Especially in a star where masses are large enough to result in densities sufficient to cause fusion - and large releases of heat, which then cause decreased density, etc. But all other factors being constant, the…

Could it cool and crystallise? Could those crystals then erode and reform again as sedimentary rocks to be come a solid planets like earyh? I understand that’s not how earth itself came to be, but it’s an interesting metamorphosis that I hadn’t previously considered.

At the point hydrogen, helium, ammonia, etc. have cooled to solid ‘rock’, chemistry and weather as we’re familiar with it doesn’t really apply anymore. Pluto has been that way for a long time though, albeit good luck spending enough time there to get very familiar with it.

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#19

Post by yubblegum »

I've always wondered about the core of these gas giants. I assume it is some liquid form of light elements. What is puzzling is the presence of the gas giants in the middle of solar system's planetary line up: why are they in the middle and the ones closer or further away from the central star are not like them? Is it the temperature gradient?

Re: Jupiter was formerly twice its current size, had a much stronger magnetic field

#20

Post by fasteddie31003 »

I am deeply skeptical of any "research" that concludes something in the past. The scientific method relies on observation, experimentation, and replication, but these aren't possible with past events, so we can't directly test or falsify historical claims. Instead, researchers infer conclusions based on indirect evidence like documents, artifacts, or statistical patterns—often without being able to isolate variables or rule out alternatives.

If something is not falsifiable, it is not science in my book. Research that is falsifiable uncovers deep truths of nature that will benefit humanity's progress, which this kind of research will not.

Sorry to be a downer. I haven't had my morning coffee yet.

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