Jupiter was once twice its current size, study reveals – how did it shrink?

Jupiter Was Once Twice Its Size, Say Scientists (Image: Canva)

When you were a kid, you could've envisioned Jupiter as a giant of planets. As it happens, your imagination wasn't so far-fetched. Recent studies now indicate that this gas giant was much larger in its early days — perhaps more than double its present size.

Jupiter's Massive Past

A Caltech and University of Michigan study shows that Jupiter, the Solar System's heavyweight already, would have been able to contain 2,000 Earths within it at one time. That enormous size gradually decreased as the planet cooled and shrunk. They made their discovery, reported in Nature Astronomy, providing a new window into the early evolution of the Solar System, sometime about 3.8 million years after solids first formed.

Jupiter's vast gravity assisted the sculpting of orbits for other developing planets. Being the initial planet to develop, it assisted in determining the structure of our solar system. Caltech Professor Konstantin Batygin, co-author of the study, states that this work assists in tracing our beginnings and understanding planetary development better.

Moons Reveal the Clues

Scientists focused on Jupiter's little moons Amalthea and Thebe. Their peculiar orbits didn't quite fit with Jupiter's current size. Rather than solely depending on planet formation theories, the group examined observable information such as angular momentum and moon dynamics.

Their math indicates that 4.5 billion years ago, Jupiter's radius was as much as 2.5 times its modern value. Its magnetic field, already 20,000 times Earth's, may have been 50 times stronger then.

Shaping the Solar System

These discoveries alter the way that we envision the early solar system. Around then, a massive ring of gas and dust known as the protoplanetary disc encircled the Sun. It was from this disc that planets formed.

The findings agree with the generally accepted core-accretion model. According to this model, giant planets such as Jupiter formed as solid cores, which then attracted nearby gases. When their mass accumulated to some threshold, accretion of gas proceeded at a furious rate.

Although the actual planet-building process is still controversial, the researchers feel that their measurements provide a defining landmark. These accurate measurements of Jupiter's initial size, rotation, and magnetism will inform future research.

Professor Batygin says this benchmark brings us a step closer to piecing together the evolution of the Solar System and our place in it.