EMBRYO IMPACTS AND GAS GIANT MERGERS. I. DICHOTOMY OF JUPITER AND SATURN's CORE MASS

Li, Shu Lin; Agnor, C. B.; Lin, D. N. C.

doi:10.1088/0004-637x/720/2/1161

Cited by 22 publications

(25 citation statements)

References 79 publications

(107 reference statements)

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“…For an alternative idea of a large core of Saturn, Li, Agnor & Lin (2010) suggested that Saturn might have experienced the impact of a (proto‐) gas giant and then merged. It is still an open question as to whether such an impact on Saturn happened in reality in a multiple‐protoplanet system.…”

Section: Discussionmentioning

confidence: 99%

Gas giant formation with small cores triggered by envelope pollution by icy planetesimals

Hori¹,

Ikoma²

2011

Monthly Notices of the Royal Astronomical Society

131

138

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We have investigated how envelope pollution by icy planetesimals affects the critical core mass for gas giant formation and the gas accretion time‐scales. In the core‐accretion model, runaway gas accretion is triggered after a core reaches a critical core mass. All the previous studies on the core‐accretion model assumed that the envelope has the solar composition uniformly. In fact, the envelope is likely polluted by evaporated materials of icy planetesimals because icy planetesimals going through the envelope experience mass‐loss via strong ablation and most of their masses are deposited in the deep envelope. In this paper, we have demonstrated that envelope pollution in general lowers the critical core masses and hastens gas accretion on to the protoplanet because of the increase in the molecular weight and reduction in the adiabatic temperature gradient. Widely and highly polluted envelopes allow smaller cores to form massive envelopes before disc dissipation. Our results suggest that envelope pollution in the course of planetary accretion has the potential to trigger gas giant formation with small cores. We propose that it is necessary to take into account envelope pollution by icy planetesimals when we discuss gas giant formation based on the core accretion model.

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Section: Discussionmentioning

confidence: 99%

Gas giant formation with small cores triggered by envelope pollution by icy planetesimals

Hori¹,

Ikoma²

2011

Monthly Notices of the Royal Astronomical Society

131

138

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“…One hypothesis is that they arise as mergers of two or more less massive cores. The merging processes tend to merge the denser cores together but (partially) erode their gas envelopes (99,100), resulting in a net mass increase accompanied by a very small radius increase, that moves them to the right on the mass-radius diagram. Disks with high metallicity may facilitate mergers.…”

Section: Transitional Planetsmentioning

confidence: 99%

Growth model interpretation of planet size distribution

Zeng

Jacobsen

Sasselov

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

414

342

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The radii and orbital periods of 4000+ confirmed/candidate exoplanets have been precisely measured by the Kepler mission. The radii show a bimodal distribution, with two peaks corresponding to smaller planets (likely rocky) and larger intermediate-size planets, respectively. While only the masses of the planets orbiting the brightest stars can be determined by ground-based spectroscopic observations, these observations allow calculation of their average densities placing constraints on the bulk compositions and internal structures. Yet an important question about the composition of planets ranging from 2 to 4 Earth radii (RÅ) still remains. They may either have a rocky core enveloped in a H2-He gaseous envelope (gas dwarfs) or contain a significant amount of multi-component, H2O-dominated ices/fluids (water worlds). Planets in the mass range of 10-15 MÅ, if half-ice and half-rock by mass, have radii of 2.5 RÅ, which exactly match the second peak of the exoplanet radius bimodal distribution. Any planet in the 2-4 RÅ range requires a gas envelope of at most a few mass%, regardless of the core composition. To resolve the ambiguity of internal compositions, we use a growth model and conduct Monte Carlo simulations to demonstrate that many intermediate-size planets are "water worlds". Keywords: exoplanets / bimodal distribution / ices / water worlds / planet formation Significance Statement: The discovery of numerous exoplanet systems containing diverse populations of planets orbiting very close to their host stars challenges the planet formation theories based on the Solar system. Here we focus on the planets with radii of 2-4 RÅ, whose compositions are debated. They are thought to be either gas dwarfs consisting of rocky cores embedded in H2-rich gas envelopes or water worlds containing significant amounts of H2Odominated fluid/ice in addition to rock and gas. We argue that these planets are water worlds.

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“…Giant impacts 19,20 are likely to occur shortly after runaway gas accretion when a gas giant planet's gravitational perturbation significantly intensifies (about thirty-time increases in a fraction of a million years) and therefore destabilizes the orbits of nearby protoplanetary embryos. This transition follows oligarchic growth 21 and the emergence of multiple embryos with isolation mass in excess of a few M ⊕ 22 .…”

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confidence: 99%

The formation of Jupiter’s diluted core by a giant impact

Liu

Hori

Müller

et al. 2019

Nature

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The Juno mission 1 is designed to measure Jupiter's gravitational field with an extraordinary precision 2. Structure models of Jupiter that fit Juno gravity data suggest that Jupiter could have a diluted core and a total heavy-element mass M Z ranging from ten to two dozens of Earth masses (∼ 10 − 24M ⊕). In that case the heavy elements are distributed within an extended region with a size of nearly half of Jupiter's radius R J 3, 4. Planet formation models indicate that most of the heavy elements are accreted onto a compact core 5-7 , and that almost no solids are accreted during runaway gas accretion (mainly hydrogen and helium, hereafter H-He), regardless to whether the accreted solids are planetesimals or pebbles 8-10. Therefore, the inferred heavy-element mass in the planet cannot significantly exceeds the core's mass. The fact that Jupiter's core could be diluted, and yet, the estimated total heavy-element mass in the planet is relatively large challenges planet formation theory. A possible explanation is erosion of the compact heavy-element core. Its efficiency, however, is uncertain and depends on both the immiscibility of heavy materials in metallic hydrogen and the efficiency 1

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EMBRYO IMPACTS AND GAS GIANT MERGERS. I. DICHOTOMY OF JUPITER AND SATURN's CORE MASS

Cited by 22 publications

References 79 publications

Gas giant formation with small cores triggered by envelope pollution by icy planetesimals

Gas giant formation with small cores triggered by envelope pollution by icy planetesimals

Growth model interpretation of planet size distribution

The formation of Jupiter’s diluted core by a giant impact

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