Saturn is said to eat his offspring in Greek mythology. Jupiter, on the other hand, turns out to be the one that eats the infant planets.

Researchers analysing data from Nasa’s Juno spacecraft discovered Jupiter’s core is more massive than certain previous theories of the gas giant’s origin would have anticipated in a new report published in the journal Icarus.

One theory is that Jupiter ate planetesimals — or tiny planets — in the past, transforming them into a centre of mass that pulled in the rest of the material that eventually created the large planet.

Jupiter is the Solar System’s biggest planet, with twice the mass of all the other planets combined, and has sucked up most of the hydrogen gas left over after the Sun’s birth.

That plentiful hydrogen makes up the vast majority of Jupiter’s immense atmosphere, and at higher depths, it is liquified by pressure into a large ocean of electrically conductive, metallic liquid hydrogen, which is the source of the big planet’s massive magnetic field.

According to some ideas, Jupiter formed from a huge cloud of gas, with parts of the cloud spinning tighter and increasing in mass until they collapsed in on themselves, similar to how stars develop, but without getting large enough to initiate a thermonuclear explosion and become a tiny star. Other hypotheses propose that tiny, cold space objects collided and created a small rocky seed around which Jupiter as we know it solidified.

However, it is unknown whether Jupiter has a compact rocky core or a larger “fuzzy” core made up of heavy elements diluted by hydrogen and helium. “There is no one answer for Jupiter’s interior structure,” the researchers write in their new report, “and more than one density profile can fulfil all the observational constraints.”

Much of what scientists know about Jupiter’s interior comes from NASA’s Juno probe, which has been circling and researching the gas giant since 2016.

The researchers discovered an oddity when analysing the Juno data: earlier models showed Jupiter’s core, whatever it is made of, takes up around 10% of the planet’s mass. However, the researchers discovered that this area accounts for 30% or more of the planet’s mass in their revised models based on Juno data, reflecting a greater than anticipated proportion of heavier components than hydrogen and helium.

Several scenarios might explain the new model, but the researchers choose the one they believe is most likely: Jupiter’s early expansion could have been powered by collisions between much larger planetesimals, rather than by the agglomeration of microscopic space rocks.

This would explain the heavier metals discovered in Jupiter’s core, but it might also have far-reaching ramifications for our understanding of planet formation around the Sun and other stars.
Scientists know that Jupiter’s gravity influenced the creation and orbits of other planets, and that comparable influences may be exerted by huge, early-forming gas giants in other star systems.

However, if gas giants must also eat planetesimals that might one day evolve into rocky planets like Earth if they survive, then gas giants may have far greater impact over the formation of other planets — and life as we know it — than previously imagined.

There are alternative, if less likely, theories for Jupiter’s heavy centre, according to the researchers, including a massive impact by a huge rocky body during Jupiter’s early years.

“Future high-resolution investigations of planet-forming zones surrounding other stars, from observed and modelled designs of extrasolar systems with large planets, and future Juno data gathered during its extended mission,” they write, will be needed to know for sure.