Juno alongside Jupiter
Source: Business Insider

In Roman mythology, the god Jupiter, who was fond of mortal woman, would hide his misdeeds by wrapping himself in clouds. Every time, like a wife following her husband to the casino, the goddess Juno would unveil his guilty secrets by peeking through the clouds. Now life is repeating mythology as NASA’s Juno spacecraft uncovers the ancient secrets hidden deep inside the core of Jupiter, the largest planet in the Solar System. Recently Juno hit the scientific jackpot with the sensational revelation of 4.5 billion year old collision that changed the entire history of the Solar System.

 A puzzle at the core

Juno entered Jupiter’s orbit in July 2016. Apart from capturing the most stunning images of the gas giant that we have yet, Juno measured the planet’s gravitational field. This resulted in a surprising discovery that raised more questions than it answered. Researchers at Rice University looked at Juno’s data about Jupiter’s gravity and realised that instead of a small, dense core as previously thought, the titanic planet has a larger, diluted, “fuzzy” core instead. This suggests that in addition to rocks and ices, the core is mixed with less-dense hydrogen and helium. 

“It suggests that something happened that stirred up the core,” said astronomer Andrea Isella.

Until now, scientists believed that Jupiter began its career as a dense, frozen, rocky world that over time collected tremendous quantities of gas from the Solar System’s primordial disk. Enormous gravity and pressure should have given the core a smooth surface. To explain the difference between this theory and what the Juno spacecraft has found, scientists have proposed a dramatic theory. The surprising form of Jupiter’s core could be the result of a massive impact between Jupiter and a large body.

“[A] sufficiently energetic head-on collision (giant impact) between a large planetary embryo and the proto-Jupiter could have shattered its primordial compact core and mixed the heavy elements with the inner envelope,” states a research article in the journal Nature.

The unique gravitational field of Jupiter
Source: Business Insider

When worlds collide

To better understand what happened, researchers at Rice University conducted a series of virtual simulations. They wanted to know how the theoretical collision could produce the “fuzzy” core that the Juno spacecraft observed. In the simulations, when large bodies impacted Jupiter at an angle, they were swallowed up in the planet’s powerful gravitational field. When Earth-sized bodies hit Jupiter directly, they simply disintegrated in the massive world’s atmosphere.

Eventually, the team found that the “fuzzy” core could have been produced by a planet ten times the mass of Earth smashing head-on into Jupiter 4.5 billion years ago and mixing dense layers in the deep core with less-dense material nearer the surface. 

“Because it’s dense, and it comes in with a lot of energy, the impactor would be like a bullet that goes through the atmosphere and hits the core head-on. Before impact, you have a very dense core, surrounded by atmosphere. The head-on impact spreads things out, diluting the core,” Isella said.

Changing solar history

Because Jupiter is so incredibly huge, it has a big influence on all the other bodies in the Solar System. This means that a change in its gravity would have changed how the other planets in the Solar System developed. The small planetary embryos would have been drawn towards the gas giant as it expanded. Jupiter’s tremendous mass would also have acted as a focus for incoming bodies. Head-on collisions would have been much more frequent.

As for Juno, the intrepid spacecraft will orbit Jupiter until July 2021 before diving into the gas giant’s atmosphere. This will destroy the vehicle and prevent any microbes that may have accompanied the spacecraft from contaminating any of Jupiter’s moons.