Original title: Beyond Pebble Isolation: Diverse Pathways to Giant Planet Formation Across Stellar and Orbital Scales
Lorenzo Peerani, Sho Shibata, Ravit Helled · September 2026
Giant planets need to gather a thick gas envelope equal to their core mass before their surrounding birth disc disappears. Scientists studied how these planets form across different distances around stars of 0.1-1.5 Msun. They simulated growing planets by pebble accretionProcess where a rocky core grows by sweeping up small particles (pebbles) from the surrounding disc., where small rocky bits pile up into a solid core that pulls in gas. They found that giant planets easily form far from their stars, but they cannot form in-place close to their stars. Close in, disc heating keeps the gas too hot to cool and collapse onto the core. This shows that hot giant planets likely formed farther out and migrated inward. Farther out, cold conditions let the gas cool quickly. This allows giant planets to trigger runaway gas growth early, producing giant planets with cores ranging between 0.7 and 20 M_Earth.
You are trying to inflate a giant balloon from a small rubber ball by adding gas. The problem is that if the air around you is very hot, the gas expands and escapes before the balloon grows. In this paper, the researchers modeled planet formation: in hot inner discs the gas escapes, so giant planets there cannot form on the spot — they must have inflated elsewhere and moved in. In cold outer discs, the gas stays and inflates the balloon easily, so a giant planet can form even if the rubber ball (the core) is very small.
This research explains why some giant planets have surprisingly tiny cores, and why hot Jupiters likely formed far out and migrated inward. It shows that formation conditions—especially temperature and distance from the star—determine whether a planet grows a big or small core. That helps astronomers understand why exoplanets are so diverse inside.
The model only simulates formation up to crossover mass, not later stages like runaway gas accretion or orbital evolution. It considers pebble accretion but not other core growth mechanisms like planetesimal impacts. The results depend on the chosen disc properties and opacity assumptions, and they apply to the specific range of stellar masses and orbital distances studied.
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Beyond Pebble Isolation: Diverse Pathways to Giant Planet Formation Across Stellar and Orbital Scales — Lorenzo Peerani, Sho Shibata, Ravit Helled
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.