In its distant past, Jupiter may have been something of a planetary cannibal—and its core paid the ultimate price.
A new computer simulation published yesterday in the journal Nature suggests that some 4.5 billion years ago, a youthful Jupiter may have collided with another primordial planetary body. This violent rendezvous likely ended in Jupiter swallowing its dance partner whole—a merger that fractured Jupiter’s hard, compact core into the diffuse, borderless ball of gassy fluff it still has today.
Prior to NASA’s recent Juno mission, researchers assumed that Jupiter’s core was a solid pit of rock and ice—a dense seed that was able to attract clouds of hydrogen and helium with its gravitational pull. But the spacecraft’s measurements of the gas giant’s gravitational field in 2016 painted a very different portrait, with no clear delineation between the core and its gas envelope. Jupiter’s heart, it seems, is hazy, dilute, and massive, spanning up to half the planet’s radius.
Though there’s no time machine that can transport researchers back to the era of Jupiter’s genesis, the new model—the brainchild of a team of researchers led by Shang-Fei Liu of Sun Yat-sen University—offers a possible explanation for this puzzling observation.
The early days of the solar system were an especially tumultuous time. Space rocks ricocheted about; primitive planetary bodies crashed together and came apart. Even in its fetal state, Jupiter was the heftiest kid on the block, boasting a gravitational pull that could have easily sucked in another cosmic nugget on the rise, study author Andrea Isella, an astronomer at Rice University in Houston, told Maria Temming at Science News.
In the researchers’ proposed scenario, this object was about 10 times as massive as Earth (for perspective, Jupiter’s mass is more than 300 times that of our home planet), and “smacked head-on” into the growing gas giant, Liu told Chelsea Gohd at Space.com.
As the ill-fated planetary embryo was absorbed into Jupiter, the pair’s cores combined, their materials mingling with heavy elements in the newly-expanded planet’s gaseous sheath. As a result, the diameter of Jupiter’s core more than doubled.
The model isn’t easy to confirm, and it’s not the only theory that’s been put forth. Other researchers have suggested that Jupiter’s dilute core has a more mundane origin: Gas may have been present in the core from the start, rather than glomming on during the planet’s adolescence, for instance.
More computer simulations could help researchers compare these competing theories, Juno mission leader Scott Bolton of the Southwest Research Institute in San Antonio, who wasn’t involved in the study, told Temming.
If the impact scenario is correct, though, it might not actually be that big of a surprise. Researchers have long been aware of the solar system’s chaotic beginnings, and few planets—if any—escaped unscathed. Even Earth’s moon might not be around if not for a calamitous collision.
What’s more, the internal structure of several planets, including Saturn, Uranus, and Neptune, remain vastly unexplored. Jupiter’s quirky core may yet be par for the course.