Just 3.8 million years after the solar system’s first solids formed, Jupiter was still roughly twice its current radius and its surface magnetic field was about 50 times stronger — conclusions a 2025 Nature Astronomy study reconstructed partly from the slight orbital tilts of two tiny inner moons, Amalthea and Thebe.
Jupiter left no photograph of its infancy. It did, however, leave a dynamical problem in two small moons…
