Giant planet Jupiter used to be TWICE as big

Jupiter, the biggest planet in our solar system, used to be even bigger.

Scientists researching the planet have discovered that the young Jupiter was roughly double the size it is today.

Just 3.8 million years after the very first solid objects started to form in space, Jupiter had a radius (that's how far it is from the centre to its outside edge) that was nearly twice as big.

That means over 2,000 Earths could fit inside it. Whereas today, it can fit about 1,321 Earths - still huge, but not quite as big as before.

To find this out, a team of scientists led by Professor Konstantin Batygin from the California Institute of Technology didn't look at Jupiter directly.

Instead, they studied two of its tiny moons called Amalthea and Thebe.

These moons are really close to Jupiter and have been moving around the planet in orbit in the same way since the early days of the solar system - like two walkers moving in a circle but never changing their steps.

When a moon goes around a planet, it usually follows a flat path, like a ring around a hula hoop.

But when Jupiter was much bigger, it had a super strong magnetic field - like a mega magnet.

These magnetic forces were strong enough to nudge the moons' orbits just a tiny bit, tilting them.

Once the tilted orbit happens, it can continue that way for billions of years. And tracing those movements helped the scientists work out that Jupiter used to be much, much bigger.

Professor Batygin says the study, "brings us closer to understanding how not only Jupiter but the entire solar system took shape."