Weiss & Bottke (2021) synthesized meteorite paleomagnetic records to propose that proto-Jupiter grew from roughly 50 Earth masses at more than 3.46 million years (Myr) after the first solids to its final 318 Earth masses in under 0.5 Myr, and stated the assumptions this growth history rests on: that the gap separating the non-carbonaceous (NC) and carbonaceous (CC) meteorite isotopic reservoirs was opened by proto-Jupiter, with inter-reservoir contamination consistent with the isotopic data; that a meteorite's magnetic record represents nebular conditions throughout its parent reservoir, so predicted field–distance relations constrain formation distances; and that the inferred slow-then-rapid gas accretion can be reconciled with formation models in which substantial planetary migration suppresses the slow-accretion phase. As of August 2026, all three assumptions remain unresolved: alternative barrier mechanisms (condensation-front pressure bumps, evaporation-driven processing, inherited cloud heterogeneity) compete with the Jupiter-gap hypothesis, and dust-leakage models reach conflicting verdicts on contamination consistency; new paleomagnetic data (CO chondrites, chondrule reanalyses, Erg Chech 002, Ryugu, calcium-aluminum-rich inclusions) have not validated the representativeness assumption or the field–distance calibration; and no published work reconciles the meteorite chronology with migration-dominated growth. The problem—validate or refute the proposed growth history of Jupiter—remains a precise and open target.

Background

Jupiter is the benchmark case for the core-accretion model of giant-planet formation, in which a solid core first accretes planetesimals and pebbles (centimeter-to-meter solids that drift through the gas), then slowly accumulates a hydrogen-helium envelope, and finally undergoes runaway gas accretion once the envelope mass becomes comparable to the core mass. Meteorites carry time markers for this history. Bulk meteorites divide into two isotopically distinct superfamilies—non-carbonaceous (NC) and carbonaceous (CC)—separated by mass-independent (nucleosynthetic) isotope anomalies (for example in ε54\varepsilon^{54}Cr, ε50\varepsilon^{50}Ti, and ε92\varepsilon^{92}Mo, where the ε\varepsilon notation denotes deviations in parts per ten thousand from terrestrial composition) that trace the presolar dust mixture from which each parent body formed. NC meteorites (ordinary and enstatite chondrites, most irons, and the building blocks of Earth and Mars) sample the inner solar system, while CC meteorites sample material formed farther out. Because the two reservoirs coexisted for several million years (Myr) yet remained isotopically distinct, a long-lived physical barrier in the solar nebula (the gas disk around the young Sun) has long been invoked. Kruijer et al. (2017) proposed that proto-Jupiter, formed within about 1 Myr of the first solids (calcium-aluminum-rich inclusions, CAIs, the oldest dated solar system objects), opened a gap—a torus of depleted gas and dust that a sufficiently massive planet carves by its gravitational torques—that separated inner from outer solids and created the two reservoirs.

Paleomagnetism supplies an independent chronometer. Some meteorites retain thermoremanent or chemical remanent magnetizations recording the solar nebula's magnetic field, whose strength is recovered by paleointensity analysis; because the nebular field is sustained by disk gas, its disappearance dates gas dispersal. Weiss & Bottke (2021) synthesized such records and argued that, under stated testable assumptions, proto-Jupiter grew from about 50 Earth masses (M⊕M_\oplus) at more than 3.46 Myr after CAIs to its final 318 M⊕M_\oplus in under 0.5 Myr—an acceleration matching the runaway-gas-accretion prediction of core accretion. A key input is the relation between nebular field strength and heliocentric distance predicted by disk magnetohydrodynamics models, which lets a paleointensity be read as a formation distance if the disk field structure is known. Pebble drift complicates the picture: millimeter-sized solids drift inward through the gas, so any barrier must filter or pass them in proportions consistent with the measured isotope anomalies of both reservoirs.

The causal claim is nevertheless contested. Pressure bumps at sublimation fronts (for example the water snowline) can also trap drifting dust and form planetesimal rings reproducing the inner solar system's architecture and isotopic signatures without an early Jupiter gap (Izidoro et al. 2022); evaporation-driven chemical processing near the disk's hot inner region can bifurcate the compositions of planetary building blocks (Lichtenberg et al. 2021); and 'inheritance' models attribute the heterogeneity to isotopically variable infall from the parent molecular cloud rather than to later disk-scale unmixing (reviewed by Tissot et al. 2025). Whether proto-Jupiter's gap caused the dichotomy, whether meteorite magnetic records can be inverted for formation distances, and whether the inferred growth timescale survives inclusion of planetary migration therefore remain open questions that jointly determine whether the proposed growth history of Jupiter stands. Weiss & Bottke (2021) identify the measurements needed to test these assumptions: further paleomagnetic measurements, dynamical models of planetesimal scattering and collisional evolution coupled to dust and isotope transport, and spatially resolved observations of disk substructures in protoplanetary disks.

Problem Statement

The problem, as posed in Weiss & Bottke (2021), is to validate or refute the proposed growth history of Jupiter—separation of the NC and CC isotopic reservoirs by a gap opened by proto-Jupiter, followed by rapid final gas accretion beginning more than 3.46 Myr after CAI formation—by resolving three testable, linked assumptions:

  1. Causality of the gap. Establish whether the barrier that separated the non-carbonaceous and carbonaceous reservoirs was indeed opened by proto-Jupiter (rather than pressure bumps at condensation fronts, evaporation-driven processing, or heterogeneity inherited from infall), and whether the scattering and collisional/dust transport of material from the carbonaceous reservoir into the non-carbonaceous reservoir occurred at a level consistent with the measured isotopic compositions of both reservoirs.

  2. Locations of the magnetic records. Determine where in the solar system individual meteorites acquired their magnetic records—testing the assumption that a given meteorite's paleomagnetic record represents nebular conditions throughout its parent reservoir, particularly for the outer solar system—and place firm constraints on parent-body formation distances using predicted magnetic field–distance relations.

  3. Compatibility with migration. Reconcile the meteorite-derived growth chronology—a roughly 50-Earth-mass proto-Jupiter persisting beyond 3.46 Myr after CAIs followed by runaway gas accretion within 0.5 Myr—with formation models in which substantial planetary migration suppresses or removes the extended slow-gas-accretion phase.

The three components support one objective: a self-consistent, evidence-based growth history of Jupiter (or a demonstration that the meteorite record requires a different barrier and timeline). The three assumptions are independently refutable: overturning any single one of them—for example, by establishing that the barrier that separated the two reservoirs was not opened by proto-Jupiter—resolves the task on its own by refuting, or failing to validate, the proposed growth history, so settling the other two assumptions is not a precondition for such an answer.

References

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