A study published in Nature Astronomy posits that Jupiter was significantly larger earlier in its history and its more powerful magnetic field greatly influenced the formation of the solar system.
"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," Konstantin Batygi 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.
It's like a 4.5bn year-old cold case—and rocks don't lie: "Batygin emphasizes that while Jupiter's first moments remain obscured by uncertainty, the current research significantly clarifies our picture of the planet's critical developmental stages."
The formation and early evolution of Jupiter played a pivotal role in sculpting the large-scale architecture of the Solar System, intertwining the narrative of Jovian early years with the broader story of the Solar System's origins. The details and chronology of Jupiter's formation, however, remain elusive, primarily due to the inherent uncertainties of accretionary models, highlighting the need for independent constraints. Here we show that, by analysing the dynamics of Jupiter's satellites concurrently with its angular-momentum budget, we can infer Jupiter's radius and interior state at the time of the protosolar nebula's dissipation. In particular, our calculations reveal that Jupiter was 2 to 2.5 times as large as it is today, 3.8 Myr after the formation of the first solids in the Solar System. Our model further indicates that young Jupiter possessed a magnetic field of B♃† ≈ 21 mT (a factor of ~ 50 higher than its present-day value) and was accreting material through a circum-Jovian disk at a rate of –2.4 M♃ Myr−1. Our findings are fully consistent with the core-accretion theory of giant-planet formation and provide an evolutionary snapshot that pins down properties of the Jovian system at the end of the protosolar nebula's lifetime.
What happened to all that mass? It's still there—the planet got denser. Jupiter got cut.
"Determination of Jupiter's Primordial Physical State." [nature.com]
