A new study has revealed that Jupiter—our solar system’s largest planet—was once even more enormous than it is today.
In fact, around 3.8 million years after the first solid materials in the solar system formed, Jupiter was roughly twice its current size and had a magnetic field 50 times stronger.
The study, published in Nature Astronomy, was conducted by planetary scientists Konstantin Batygin from Caltech and Fred C. Adams from the University of Michigan.
Their goal was to better understand the early evolution of Jupiter, which holds key clues to how the entire solar system took shape.
Jupiter is often called the “architect” of the solar system because its strong gravity helped shape the orbits of other planets and influenced the structure of the gas and dust disk around the young sun. That disk, known as the protoplanetary nebula, was the source of material for planet formation.
Batygin and Adams looked at the orbits of two of Jupiter’s small inner moons, Amalthea and Thebe.
These moons, which lie closer to Jupiter than the well-known Galilean moons, have slightly tilted orbits.
By studying those small tilts, the researchers were able to calculate how large Jupiter must have been when the gas around the sun was disappearing. Their analysis showed that Jupiter once had a volume equal to over 2,000 Earths.
The researchers also discovered that Jupiter’s magnetic field was dramatically stronger during this early period. These findings are important because they help us understand not only Jupiter’s early days but also the critical moment when the solar system’s structure was solidified.
What makes this study stand out is how it avoids relying on uncertain parts of traditional planet formation models. Usually, scientists have to guess at things like how fast gas was added to the growing planet or what its core was made of. Instead, Batygin and Adams based their analysis on directly measurable things like the motion of Jupiter’s moons and the planet’s angular momentum, which is a measure of how fast it spins.
This gives scientists a more reliable snapshot of what Jupiter was like at a key point in the solar system’s history—just as the solar nebula was evaporating and no more planets could form.
While we still don’t know everything about how Jupiter first came to be, this new research brings us closer to understanding the earliest chapters in the story of our solar system.
As Batygin puts it, this study offers a solid starting point for exploring how the planets—and perhaps even life—came to exist.
