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We study the initial development, structure and evolution of protoplanetaryclumps formed in 3D resistive MHD simulations of self-gravitating disks. Themagnetic field grows by means of the recently identified gravitationalinstability dynamo (Riols & Latter 2018; Deng et al. 2020). Clumps areidentified and their evolution is tracked finely both backward and forward intime. Their properties and evolutionary path is compared to clumps in companionsimulations without magnetic fields. We find that magnetic and rotationalenergy are important in the clumps' outer regions, while in the cores, despiteappreciable magnetic field amplification, thermal pressure is most important incounteracting gravity. Turbulent kinetic energy is of a smaller scale thanmagnetic energy in the clumps. Compared to non-magnetized clumps, rotation isless prominent, which results in lower angular momentum in much betteragreement with observations. In order to understand the very low sub-Jovianmasses of clumps forming in MHD simulations, we revisit the perturbation theoryof magnetized sheets finding support for a previously proposed magneticdestabilization in low-shear regions. This can help explaining whyfragmentation ensues on a scale more than an order of magnitude smaller thanthat of the Toomre mass. The smaller fragmentation scale and the high magneticpressure in clumps' envelopes explain why clumps in magnetized disks aretypically in the super-Earth to Neptune mass regime rather than Super-Jupitersas in conventional disk instability. Our findings put forward a viablealternative to core accretion to explain widespread formation ofintermediate-mass planets.

Characterizing fragmentation and sub-Jovian clump properties in magnetized young protoplanetary disks