A planetary body may have smashed into Jupiter, creating its weird core

A planetary smashup billions of years ago may be to blame for Jupiter’s weirdly puffy core.

Recent measurements of Jupiter’s gravitational field indicate that, rather than a dense pit of rock and ice, Jupiter’s core is a haze of heavy elements possibly spanning half the planet’s radius (SN: 6/24/17, p. 14). That observation, made by NASA’s Juno spacecraft that started orbiting Jupiter in 2016, flies in the face of current planet formation models (SN: 6/25/16, p. 16). Those models suggest that Jupiter would have formed from a dense kernel that accumulated a thick envelope of gas.

New computer simulations now show that a collision between Jupiter and another large planetary body could have shattered Jupiter’s original compact core into the scattered collection of heavy elements seen today. Understanding the origins of Jupiter’s internal structure may give insight into the processes that shape other gas giants in our solar system and around other stars, researchers report in the Aug. 15 Nature.

“This impact may have happened when the solar system was very, very young, and in a chaotic phase when there were lots of objects roaming around,” says Andrea Isella, an astronomer at Rice University in Houston. As the biggest planetary body in its neighborhood, Jupiter was liable to gravitationally attract other objects wandering the solar system, he says.

In the simulations, Isella and colleagues found that a planetary body of about 10 Earth masses could have broken apart and merged with Jupiter’s dense core, causing that jumble of material to mix into the planet’s inner gaseous envelope. Within hours, the merger would have transformed Jupiter’s original core, around only 15 percent the planet’s radius, into a dilute core that extended to nearly half of Jupiter’s radius. Further simulations confirmed that this diffuse core could have persisted for over 4 billion years to the present day.

The idea that a giant impact reshaped Jupiter’s internal structure is plausible, says Juno mission leader Scott Bolton of the Southwest Research Institute in San Antonio, who wasn’t involved in the study. But other scenarios — such as heavy elements mixing with gas during Jupiter’s formation, or an internal churning process dredging up core material — may also explain Jupiter’s diffuse core. Computer simulations of those competing scenarios may help scientists tease out which is most likely, Bolton says, noting that figuring out how Jupiter formed and evolved is very much “a work in progress.”