The mystery of how Jupiter grew so massive is being rewritten

Space · Published 26 October 2026 Swipe more like this →

In short: For years, scientists were baffled by Jupiter's size. As a gas giant, it shouldn't have had enough time to build its massive core before the solar nebula dissipated. New astronomical observations are now overturning old theories and revealing a complex history of how our solar system's gatekeeper came to dominate.

The traditional view held that Jupiter formed through simple condensation from the primordial solar nebula, which would mean its chemical makeup should mirror the Sun's. However, recent evidence shows that Jupiter’s elemental proportions differ significantly from solar values. This discrepancy forced a shift in the scientific understanding of how the planet reached its current scale.

Current models suggest a more dynamic process: a solid core of approximately 7 Earth masses formed first. This core was built by the accretion of large, kilometre-sized icy planetesimals. As these icy bodies collided and merged, they released gases that created an initial atmosphere around the growing core. Once the core reached a critical mass, it became powerful enough to pull in massive amounts of hydrogen and helium from the surrounding nebula.

This process explains why Jupiter is so dominant today; it accounts for more than twice the mass of all other planets combined. The planet acted as a cosmic gatekeeper during its formation, influencing every other body in the solar system. It prevented the formation of another planet between Mars and the asteroid belt and has spent billions of years catapulting comets away from Earth's orbit.

The chemistry of Jupiter’s atmosphere provides a fingerprint of this violent history. Heavy elements are enriched by a factor of about three compared to solar values, reflecting the concentration of materials in the original core. To include volatile substances like argon and molecular nitrogen, these icy planetesimals must have formed at extreme temperatures of 30 K (−400 °F) or less.

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