Jupiter grew by accretion of Planetesimals

[seigell]

Per this article in Space.com, Jupiter ate baby planets while growing.
The review of mass/magnetometer data aboard the Juno orbiter tells how the telltales of those planetesimals are still detectible under the Gas Giant's upper atmosphere.

One assertion that is puzzling:
The study discounts the probable contributions to Jupiter's mass by collecting "Space Pebbles" (boulder-sized solid masses abundant in the early Solar System) - claiming that the nascent development of the gaseous atmosphere would preclude collection / retention of those smaller bodies.

Why would the developing atmosphere have any impact on the accretion of smaller "pebbles"?? Such "pebbles" encounter and interact with the upper atmosphere by "terminal friction" that slows and ablates (aggressively) those masses - adding their constituent material to the planet's mass (even if one hot atom at a time).
It's almost as if the Space.com author implies that there is a "skin" / a surface tension that would block the "pebbles".

[notFritzArgelander]

I agree that the turn of phrase is exceedingly odd and I think unphysical.

This work is also discussed in another recent thread which has no mention of this odd effect. See https://theskysearchers.com/viewtopic.php?t=25226

Indeed while the atmosphere is collecting pebbles would behave like meteors and increase the metallicity of outer layers.

[helicon]

Thanks for posting the other thread notFritz and thanks @seigell for posting the article.

[seigell]

@nFA - The Article of your other Post has an equally mystifying comment about "Pebbles" and "Planetary Growth:

We know that once a baby planet is big enough, it starts pushing out pebbles.

No explanation is given - as if this is a well-known axiom...
Does it relate to the Atmospheric Surface Tension implied in the OP article?? Or that pebbles "splash" out of the gravity well upon "acquisition" (impact with retention) of a larger planetesimal?? (And does the latter happen in "significant" quantity to offset the accumulation of pebbles into the planetary atmosphere??)

[SkyHiker]

So, is the reaon why our gas giants are all in the outer regions, because they can accumulate more heavy material because there is more of that in their much larger orbits? Then gas will be sucked in. The inner planets can do that to a much lesser extent I would think.

[turboscrew]

Hmm, Tunguska, ... or was the atmosphere a lot thicker then, when the rocky planers developed?

Also, Jupiter doesn't contain much heavier elements, I guess.
https://en.wikipedia.org/wiki/Jupiter#Composition

[seigell]

Also, Jupiter doesn't contain much heavier elements, I guess.
https://en.wikipedia.org/wiki/Jupiter#Composition

The Wiki "Composition" section is purely referencing the Upper Atmosphere.
We can only guess at the Component Composition of the Heavier Elements which make up the "Lumpy Core", but per Juno we know that it's deep in there...

[notFritzArgelander]

Also, Jupiter doesn't contain much heavier elements, I guess.
https://en.wikipedia.org/wiki/Jupiter#Composition

The Wiki "Composition" section is purely referencing the Upper Atmosphere.
We can only guess at the Component Composition of the Heavier Elements which make up the "Lumpy Core", but per Juno we know that it's deep in there...

Quite right. The deeper layers are enriched with respect to the upper atmosphere.

[seigell]

So, is the reaon why our gas giants are all in the outer regions, because they can accumulate more heavy material because there is more of that in their much larger orbits? Then gas will be sucked in. The inner planets can do that to a much lesser extent I would think.

There are a number of theories and descriptions of the dynamics of proto-solar/planetary systems - mostly starting with a rough thick-centered rotating thick-centered spiral disc of matter.
The bulk of that matter falls into the proto-star, but at least a few uneven clumps in the spirals of the disc will also thicken with enough mass to start forming a planetesimal. Whether the "lucky" of those planetesimals continue to collect matter directly out of the cloud, or they see growth by "sticky" collisions, or most likely a combo of both mechanisms, a fair amount of the matter accumulates into certain planetary bodies (heavier elements and hydrogen / helium as dictated by the source cloud's makeup).
Shortly after the solar mass ignites, the inner planets ability to grow by accumulating directly from the cloud is curtailed as the nascent solar winds start to blast away at the inner portions of the spiral disc. Soon, those solar winds will also start eroding the upper reaches of the atmospheres that those inner planets had initially accumulated (were any of them on their way to becoming a large gaseous Planet such as the outer Ice Giants?) Perhaps this pushes more matter into the path of the median and outer orbits. Perhaps Jupiter was located rather strategically (lucky). Any telltales are open to multiple interpretations. Among those interpretations are theories whether Jupiter formed in a median orbit and then migrated inward or outward (or both) - it's gravity perturbing / pushing other planets out of the way (or even out of the Solar System).

[notFritzArgelander]

@nFA - The Article of your other Post has an equally mystifying comment about "Pebbles" and "Planetary Growth:

We know that once a baby planet is big enough, it starts pushing out pebbles.

No explanation is given - as if this is a well-known axiom...
Does it relate to the Atmospheric Surface Tension implied in the OP article?? Or that pebbles "splash" out of the gravity well upon "acquisition" (impact with retention) of a larger planetesimal?? (And does the latter happen in "significant" quantity to offset the accumulation of pebbles into the planetary atmosphere??)

Thanks for pointing out my error in reading the article. I apologize for my confusion and plead temporary dyslexia due to other matters shifting my attention. I've looked into it and think I have a better grasp of it now.

The work being reported is at https://arxiv.org/pdf/2203.01866.pdf

Context. While Jupiter’s massive gas envelope consists mainly of hydrogen and helium, the key to understanding Jupiter’s formation and evolution lies in the distribution of the remaining (heavy) elements. Before the Juno mission, the lack of high-precision gravity harmonics precluded the use of statistical analyses in a robust determination of the heavy-elements distribution in Jupiter’s envelope.

Aims. In this paper, we assemble the most comprehensive and diverse collection of Jupiter interior models to date and use it to study the distribution of heavy elements in the planet’s envelope.

Methods. We apply a Bayesian statistical approach to our interior model calculations, reproducing the Juno gravitational and atmo- spheric measurements and constraints from the deep zonal flows.

Results. Our results show that the gravity constraints lead to a deep entropy of Jupiter corresponding to a 1 bar temperature 5-15 K higher than traditionally assumed. We also find that uncertainties in the equation of state are crucial when determining the amount of heavy elements in Jupiter’s interior. Our models put an upper limit to the inner compact core of Jupiter of 7 MEarth, independently on the structure model (with or without dilute core) and the equation of state considered. Furthermore, we robustly demonstrate that Jupiter’s envelope is inhomogenous, with a heavy-element enrichment in the interior relative to the outer envelope. This implies that heavy element enrichment continued through the gas accretion phase, with important implications for the formation of giant planets in our solar system and beyond.

The rejection of pebbles is not a result of this work. Nor is it an axiom. It is simply a cited result:

The fragmentation and ablation of these solid planetesimals cause a non-homogenous
distribution of heavy elements in the envelope (Alibert et al. 2018). In contrast, in the pebble-driven scenario, fast orbital de- cay of pebbles caused by gas drag provides a continuous resup- ply of solid material that enriches the growing planet (Ormel et al. 2021). Nevertheless, the supply stops once the so-called pebble-isolation mass is reached (Lambrechts et al. 2014), after which only gas accretion continues unless or until pebbles grow to planetesimal size.

So we need to examine the work of (Lambrechts et al. 2014) also published in A&A but not in open source unfortunately so I looked it up on arXiv. (Maybe A&A only has more recent papers open source? :shrug: )

Anyway... I find https://arxiv.org/abs/1408.6087 titled "Separating gas-giant and ice-giant planets by halting pebble accretion"

In the Solar System giant planets come in two flavours: 'gas giants' (Jupiter and Saturn) with massive gas envelopes and 'ice giants' (Uranus and Neptune) with much thinner envelopes around their cores. It is poorly understood how these two classes of planets formed. High solid accretion rates, necessary to form the cores of giant planets within the life-time of protoplanetary discs, heat the envelope and prevent rapid gas contraction onto the core, unless accretion is halted. We find that, in fact, accretion of pebbles (~ cm-sized particles) is self-limiting: when a core becomes massive enough it carves a gap in the pebble disc. This halt in pebble accretion subsequently triggers the rapid collapse of the super-critical gas envelope. As opposed to gas giants, ice giants do not reach this threshold mass and can only bind low-mass envelopes that are highly enriched by water vapour from sublimated icy pebbles. This offers an explanation for the compositional difference between gas giants and ice giants in the Solar System. Furthermore, as opposed to planetesimal-driven accretion scenarios, our model allows core formation and envelope attraction within disc life-times, provided that solids in protoplanetary discs are predominantly in pebbles. Our results imply that the outer regions of planetary systems, where the mass required to halt pebble accretion is large, are dominated by ice giants and that gas-giant exoplanets in wide orbits are enriched by more than 50 Earth masses of solids.

The full version at arXiv is https://arxiv.org/pdf/1408.6087.pdf. The assumptions (or axioms if you prefer) are merely Newtonian mechanics and hydrodynamics. In the process of accreting pebbles the supply of pebbles in the protoplanetary orbit is reduced. Whether the pebbles can be resupplied depends on the interaction of the pebbles with the gas in the disk. From section 4:

We now highlight the existence of a limiting mass for giant plan- ets above which no further pebbles are accreted. Detailed 3-D numerical simulations of an annulus of the protoplanetary disc show that as the planet grows larger than the pebble isolation mass,... (equation omitted), local changes in the pressure gradient modify the rotation veloc- ity of the gas, which halts the drift of pebbles to the core (Eq. 5-6 and Fig. 2-3). The value of the pebble isolation mass depends dominantly on the orbital radius through the disc aspect ratio,...., see further Sec. 4.1. Therefore pebble isolation becomes harder to attain at wider orbital separations in flaring discs.

So it isn't the planet that does the trapping. It's the pressure gradient in the protoplanetary disk that halts pebble accretion where the disk is thin, close to the protostar. Further out the disk is thicker and the mass needed to create the pressure gradient is too high to stop pebble accretion.

[SkyHiker]

Hmm, Tunguska, ... or was the atmosphere a lot thicker then, when the rocky planers developed?

Also, Jupiter doesn't contain much heavier elements, I guess.
https://en.wikipedia.org/wiki/Jupiter#Composition

One point in the article is that Jupiter does have a relatively high number of rocky fragments IIRC. That allows it to suck in the gas. So, while it is mostly a gaseous planet, those rocky fragments are essential to make it one.

[turboscrew]

Also, Jupiter doesn't contain much heavier elements, I guess.
https://en.wikipedia.org/wiki/Jupiter#Composition

The Wiki "Composition" section is purely referencing the Upper Atmosphere.
We can only guess at the Component Composition of the Heavier Elements which make up the "Lumpy Core", but per Juno we know that it's deep in there...

"The interior of Jupiter contains denser materials—by mass it is roughly 71% hydrogen, 24% helium, and 5% other elements."

[turboscrew]

This is the newest about Jupiter's core that I found.
https://www.lpi.usra.edu/planetary_news ... uzzy-core/

[seigell]

"The interior of Jupiter contains denser materials—by mass it is roughly 71% hydrogen, 24% helium, and 5% other elements."

Yes, but given the mass of Jupiter (and Saturn), that large hydrogen/helium budget is expressed in strange ways.
While neither planet has anywhere near the mass required to start Fusion, they do compress large portions of that hydrogen to its metallic state. This is what gives each a monstrous electromagnetic dynamo.
It may be applicable to envision Jupiter's inner structure as analogous to Earth's, with metallic hydrogen replacing the rock and magma of the mantle and outer core (and Jupiter's thick atmosphere as Earth's crust/atmosphere).
For Saturn, a similar analogy with metallic hydrogen representing the outer core and liquid molecular hydrogen as the mantle.
Pressure gradients within the Gas Giants
What is metallic hydrogen, and does it exist at the core of all the gas giants in our solar system?

[turboscrew]

"The interior of Jupiter contains denser materials—by mass it is roughly 71% hydrogen, 24% helium, and 5% other elements."

Yes, but given the mass of Jupiter (and Saturn), that large hydrogen/helium budget is expressed in strange ways.
While neither planet has anywhere near the mass required to start Fusion, they do compress large portions of that hydrogen to its metallic state. This is what gives each a monstrous electromagnetic dynamo.
It may be applicable to envision Jupiter's inner structure as analogous to Earth's, with metallic hydrogen replacing the rock and magma of the mantle and outer core (and Jupiter's thick atmosphere as Earth's crust/atmosphere).
For Saturn, a similar analogy with metallic hydrogen representing the outer core and liquid molecular hydrogen as the mantle.
Pressure gradients within the Gas Giants
What is metallic hydrogen, and does it exist at the core of all the gas giants in our solar system?

It says "by mass". The densitty doesn't matter.

[seigell]

It says "by mass". The densitty doesn't matter.

Agreeing (not arguing)... Agreeing and adding interesting details of how that Hydrogen exists within the Gas Giants...