Jupiter is the largest planet in the solar system and has a mass that is 2.5x more than all the other planets put together. Most would remember that Jupiter is mostly made out of helium and hydrogen. But unlike most other gas giants, there is a significant presence of metals in the planet’s composition. Scientists have finally managed to determine where this metal in Jupiter originated from – other terrestrial planets that Jupiter consumed before they managed to fully form.

Using the Gravity Science instrument onboard NASA’s Juno probe, scientists set out to determine the composition of Jupiter. Juno, named after the Roman Goddess of the same name who was married to the Roman God Jupiter, entered the orbit of Jupiter in 2016 and used radio waves to measure the gravitational field around the planet.

Scientists have used the instruments to determine that the metallic elements found in Jupiter, which has a total mass of 11 to 30 times the mass of the Earth, were buried deep inside the planet. The metals were nearer to the centre of Jupiter than in the outer layers.

“There are two mechanisms for a gas giant like Jupiter to acquire metals during its formation: through the accretion of small pebbles or larger planetesimals,” said lead author Yamila Miguel of the study titled “Jupiter’s inhomogeneous envelope inhomogeneous envelope,” published in the journal Astronomy and Astrophysics.

“We know that once a baby planet is big enough, it starts pushing out pebbles. The richness of metals inside Jupiter that we see now is impossible to achieve before that. So we can exclude the scenario with only pebbles as solids during Jupiter’s formation. Planetesimals are too big to be blocked, so they must have played a role.”

Planetesimals are solid objects in space that form out of cosmic dust grains. Once they grow to about a kilometre in size, these planetesimals are able to use their gravitational field to grow bigger – into protoplanets.

“Our results imply that Jupiter continued to accrete heavy elements in large amounts while its hydrogen-helium envelope was growing, contrary to predictions based on the pebble-isolation mass in its simplest incarnation, favouring instead planetesimal-based or more complex hybrid models,” said Miguel.