Jupiter Was Formerly Twice Its Current Size and Had a Much Stronger Magnetic Field
NotSanguine writes:
A Caltech press release details research on the evolution of Jupiter.
From the release:
Understanding Jupiter's early evolution helps illuminate the broader story of how our solar system developed its distinct structure. Jupiter's gravity, often called the "architect" of our solar system, played a critical role in shaping the orbital paths of other planets and sculpting the disk of gas and dust from which they formed.
In a new study published in the journal Nature Astronomy, Konstantin Batygin (PhD '12), professor of planetary science at Caltech; and Fred C. Adams, professor of physics and astronomy at the University of Michigan; provide a detailed look into Jupiter's primordial state. Their calculations reveal that roughly 3.8 million years after the solar system's first solids formed-a key moment when the disk of material around the Sun, known as the protoplanetary nebula, was dissipating-Jupiter was significantly larger and had an even more powerful magnetic field.
"Our ultimate goal is to understand where we come from, and pinning down the early phases of planet formation is essential to solving the puzzle," Batygin says. "This brings us closer to understanding how not only Jupiter but the entire solar system took shape."
Batygin and Adams approached this question by studying Jupiter's tiny moons Amalthea and Thebe, which orbit even closer to Jupiter than Io, the smallest and nearest of the planet's four large Galilean moons. Because Amalthea and Thebe have slightly tilted orbits, Batygin and Adams analyzed these small orbital discrepancies to calculate Jupiter's original size: approximately twice its current radius, with a predicted volume that is the equivalent of over 2,000 Earths. The researchers also determined that Jupiter's magnetic field at that time was approximately 50 times stronger than it is today.
[...] Importantly, these insights were achieved through independent constraints that bypass traditional uncertainties in planetary formation models-which often rely on assumptions about gas opacity, accretion rate, or the mass of the heavy element core. Instead, the team focused on the orbital dynamics of Jupiter's moons and the conservation of the planet's angular momentum-quantities that are directly measurable. Their analysis establishes a clear snapshot of Jupiter at the moment the surrounding solar nebula evaporated, a pivotal transition point when the building materials for planet formation disappeared and the primordial architecture of the solar system was locked in.
Cool research with a novel methodology.
Referenced paper (Abstract)
DOI: https://doi.org/10.1038/s41550-025-02512-y
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