Researchers have proposed a possible solution to the puzzle that is Jupiter’s core. Based on data from NASA’s Juno mission, the giant planet's core is less dense than previously thought and quite extended. In the journal Nature, the team suggests that these characteristics were caused by a head-on collision with Jupiter and another planet.

According to their model, the other planet was a fledgling object expected to be about 10 times the mass of Earth: very big by our standard, but a minor contribution to a planet that today is 318 times as massive as Earth. In agreement with the thousands of simulation the team ran, this is the impact scenario that best reproduces the core we see today.

Jupiter’s core has between 10 and a few tens of Earth-mass amounts of heavy elements (anything that it is not hydrogen or helium). According to planetary formation theories, these should have settled at the very center of the planet in the early stages of Jupiter’s formation. Instead of this compact core, researchers have found evidence of heavy element regions extending to nearly half Jupiter’s radius.

“This is puzzling,” Rice astronomer and study co-author Andrea Isella said in a statement. “It suggests that something happened that stirred up the core, and that’s where the giant impact comes into play. Before impact, you have a very dense core, surrounded by an atmosphere. The head-on impact spreads things out, diluting the core.”

Isella admits that he was skeptical of the idea when he first heard it, as he considered it a one-in-trillion scenario. Lead author Shang-Fei Liu from Sun Yat-sen University convinced him “by sheer calculation”. Liu and colleagues estimated that there was at least a 40 percent chance that Jupiter swallowed a nearby forming planet within its first few million years of existence.

This work will certainly not be the last word on the subject of Jupiter’s peculiar core, and with new data constantly being received from Juno, researchers can continue to perfect models and scenarios to explain its characteristics.

Juno has been orbiting Jupiter since July 2016. Thanks to its highly eccentric orbit, the spacecraft got closer to the giant planet than ever before (snapping some pretty great photos as well). Its suite of instruments is measuring the gravitational and magnetic field of the planet, as well as its atmospheric composition.