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Grasping Jupiter’s initial evolution aids in clarifying the broader narrative of how our solar system acquired its unique configuration. Jupiter’s gravitational influence, often referred to as the “creator” of our solar system, was pivotal in forming the orbital trajectories of other planets and in shaping the disk of gas and dust from which they originated.

In a recent study published in the journal Nature Astronomy, Konstantin Batygin (PhD ’12), a professor of planetary science at Caltech, along with Fred C. Adams, a professor of physics and astronomy at the University of Michigan, present a comprehensive overview of Jupiter’s original condition. Their findings indicate that approximately 3.8 million years following the formation of the solar system’s initial solids—a critical juncture when the material disk surrounding the Sun, known as the protoplanetary nebula, was vanishing—Jupiter was substantially larger and possessed an even more intense magnetic field.

“Our primary aim is to comprehend our origins, and accurately defining the early stages of planet formation is crucial for unraveling the mystery,” Batygin remarks. “This brings us nearer to grasping how not just Jupiter, but the entire solar system came into being.”

Batygin and Adams tackled this inquiry by examining Jupiter’s diminutive moons Amalthea and Thebe, which orbit closer to Jupiter than Io, the smallest and nearest of the planet’s four principal Galilean moons. Given that Amalthea and Thebe possess slightly tilted orbits, Batygin and Adams scrutinized these minor orbital differences to estimate Jupiter’s original dimensions: roughly double its present radius, with a predicted volume that is equivalent to over 2,000 Earths. The researchers also concluded that Jupiter’s magnetic field at that time was about 50 times more powerful than it is now.

Adams emphasizes the incredible legacy the past has imprinted on today’s solar system: “It’s remarkable that even after 4.5 billion years, sufficient clues persist to enable us to reconstruct Jupiter’s physical condition at the beginning of its existence.”

Significantly, these revelations were achieved through independent parameters that circumvent traditional ambiguities in planetary formation frameworks, which often depend on assumptions regarding gas opacity, accretion rate, or the mass of the heavy element core. Rather, the team concentrated on the orbital dynamics of Jupiter’s moons and the conservation of the planet’s angular momentum—variables that are directly quantifiable. Their examination provides a distinct snapshot of Jupiter at the instant the surrounding solar nebula dissipated, a crucial transition phase when the materials for planet formation vanished and the primordial structure of the solar system was solidified.

The findings contribute essential insights to existing planet formation theories, which propose that Jupiter and other massive planets around different stars formed through core accretion, a mechanism whereby a rocky and icy core swiftly accumulates gas. These foundational frameworks have been formulated over decades by numerous researchers, including Caltech’s Dave Stevenson, the Marvin L. Goldberger Professor of Planetary Science, Emeritus. This recent study enhances that foundation by offering more precise measurements of Jupiter’s dimensions, rotation rate, and magnetic environment at an early, crucial epoch.

Batygin highlights that while Jupiter’s formative moments remain shrouded in uncertainty, the present research greatly refines our understanding of the planet’s significant developmental phases. “What we’ve established here serves as an important reference point,” he states. “A basis from which we can more assuredly retrace the evolution of our solar system.”

The paper is titled “Determination of Jupiter’s Primordial Physical State.” Funding was provided by Caltech, the David and Lucile Packard Foundation, the National Science Foundation, the University of Michigan, and the Leinweber Center for Theoretical Physics at the University of Michigan.

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