Jupiter was once twice as prominent with a supercharged magnetic field

Jupiter’s early formation shaped the structure of the Solar System, influencing its overall development. However, the exact timeline of its formation remains uncertain due to gaps in current models, making independent studies essential for a better understanding.

A new study reveals that about 3.8 million years after the Solar System began forming, Jupiter was much larger and had a stronger magnetic field than it does today. Researchers analyzed its early state, showing how it evolved as the Sun’s surrounding gas and dust, known as the protoplanetary nebula, began to fade.

Scientists studied Jupiter’s small moons, Amalthea and Thebe, to estimate their original size. Their analysis suggests that early Jupiter was twice its current radius, with a volume of over 2,000 Earths. Its magnetic field was 50 times stronger than today.

Despite 4.5 billion years of change, these findings reveal that traces of Jupiter’s ancient form still exist in the Solar System.

Jupiter like exoplanets formed earlier than previously thought

Instead of relying on uncertain planetary formation models, researchers used Jupiter’s moon orbits and angular momentum—directly measurable factors—to reconstruct its early state. Their analysis captures the moment the solar nebula evaporated, when the building materials for planets disappeared, and when the solar system’s structure was set.

The findings refine planet formation theories, supporting that Jupiter and other giant planets formed through core accretion, where a rocky core rapidly collects gas. This study builds on decades of research, offering precise measurements of Jupiter’s early size, spin rate, and magnetic field—key details in understanding the evolution of giant planets.

Konstantin Batygin (PhD’ 12), a professor of planetary science at Caltech, said, “While Jupiter’s first moments remain obscured by uncertainty, the current research significantly clarifies our picture of the planet’s critical developmental stages. What we’ve established here is a valuable benchmark—a point from which we can more confidently reconstruct the evolution of our solar system.”

Journal Reference:

1. Batygin, K., Adams, F.C. Determination of Jupiter’s primordial physical state. Nat Astron (2025). DOI: 10.1038/s41550-025-02512-y