During its formation approximately 4.5 bya, Jupiter passed through what is now the asteroid belt,gravitationally deflecting some spacewards and some sunwards. Logically, Jupiter, due to its massive gravity, must have swallowed up a fair portion as well.

Is there any way to calculate how much rock Jupiter contains? Have any estimates been made?

  • $\begingroup$ I don't think the question makes much sense. At the very least, might want to research the timeline of Jupiter formation vs. asteroid belt formation vs. settling into orbits. $\endgroup$ – Carl Witthoft Feb 12 '20 at 14:06
  • $\begingroup$ In general, that's not how gravity works. Without gas drag, it is hard for objects to hit a massive object. The most frequent outcome in close encounters between two bodies are deflections. Also it is not clear that Jupiter went through the asteroid belt. The standard Grand-tack scenario you're referring to would leave too high eccentricities and inclinations in the asteroids, which we do not observe. $\endgroup$ – AtmosphericPrisonEscape Feb 12 '20 at 15:35
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    $\begingroup$ The total mass of the asteroid belt is roughly 4% that of our Moon. Jupiter was (probably) formed with far more rocky material than that, so any swallowed asteroids would only be a small fraction of its total rock content. $\endgroup$ – PM 2Ring Feb 12 '20 at 16:42
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    $\begingroup$ Groundless criticism of this question. In the Grand Tack model (which still is the consensus despite problems), Jupiter did indeed disrupt the rocky asteroid belt and many asteroids will have ended up inside Jupiter. $\endgroup$ – ProfRob Feb 12 '20 at 21:49
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    $\begingroup$ @PM2Ring the basis of an answer. $\endgroup$ – ProfRob Feb 12 '20 at 21:50

Jupiter is a gas giant, with a mass approximately 317.8 times that of Earth, and its atmosphere has a composition that's typical of gas in space: almost 75% hydrogen and almost 24% helium, (barely different to the primordial gas created by the Big Bang). However, its interior also contains rock and metal components.

Until quite recently it was thought that Jupiter's rocky & metallic core was fairly small and compact. Various models gave estimates of a core mass ranging from 7 to 18 Earth masses. But gravitational data from the Juno mission has changed the picture rather radically. It seems that Jupiter's core is diffuse rather than compact, extending fuzzily to almost half the planet's radius! At present, we aren't quite sure of how such a core was formed, but the leading hypothesis is that Jupiter's primordial core was shattered by an extreme impact event.

From NatureDOI: 10.1038/s41586-019-1470-2 The formation of Jupiter’s diluted core by a giant impact by Shang-Fei Liu, Yasunori Hori, Andrea Isella:

The Juno mission has provided an accurate determination of Jupiter’s gravitational field, which has been used to obtain information about the planet’s composition and internal structure. Several models of Jupiter’s structure that fit the probe’s data suggest that the planet has a diluted core, with a total heavy-element mass ranging from ten to a few tens of Earth masses (about 5 to 15 per cent of the Jovian mass), and that  heavy elements (elements other than hydrogen and helium) are distributed within a region extending to nearly half of Jupiter’s radius.

Planet-formation models indicate that most heavy elements are accreted during the early stages of a planet's formation to create a relatively compact core and that almost no solids are accreted during subsequent runaway gas accretion. Jupiter’s diluted core, combined with its possible high heavy-element enrichment, thus challenges standard planet-formation theory.

A possible explanation is erosion of the initially compact heavy-element core, but the efficiency of such erosion is uncertain and depends on both the immiscibility of heavy materials in metallic hydrogen and on convective mixing as the planet evolves. Another mechanism that can explain this structure is planetesimal enrichment and vaporization during the formation process, although relevant models typically cannot produce an extended diluted core.

Here we show that a sufficiently energetic head-on collision (giant impact) between a large planetary embryo and the proto-Jupiter could have shattered its primordial compact core and mixed the heavy elements with the inner envelope. Models of such a scenario lead to an internal structure that is consistent with a diluted core, persisting over billions of years.

We suggest that collisions were common in the young Solar system and that a similar event may have also occurred for Saturn, contributing to the structural differences between Jupiter and Saturn.

In contrast, the total current mass of the asteroid belt is roughly 4% that of our Moon, so just under 0.05% of the mass of the Earth. Undoubtedly, Jupiter has swallowed numerous asteroids and comets over its lifetime, but even if it ate all of the asteroids in the asteroid belt that would only amount to less than 1% of its total rock and metal content, compared to the primordial rock and metal that it has had since its formation, including whatever rock & metal it inherited from the core impactor hypothesized by Liu et al.

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    $\begingroup$ The problem with comparing current Jupiter mass with current asteroid belt mass and then inferring conclusions about past Jupiter mass and past asteroid belt mass is that past Jupiter could be much smaller and past belt much heavier. One of the things the Grand Tack hypothesis was designed to explain is why there is so very little mass in Mars and the asteroid belt today, and that explanation was: Jupiter migrated inwards and ate or dispersed most of it. How much was ate vs. dispersed/ejected would be the relevant quantity. $\endgroup$ – zibadawa timmy Feb 14 '20 at 10:14

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