Massive Planetary Embryo Crashed into Jupiter 4.5 Billion Years Ago
An energetic head-on collision between a large planetary embryo and the proto-Jupiter about 4.5 billion years ago could explain puzzling gravitational readings from NASA’s Juno spacecraft, which suggest that Jupiter’s core is less dense and more extended that expected.
An artist’s impression of a collision between the proto-Jupiter and a massive protoplanet in the early Solar System. Image credit: K. Suda & Y. Akimoto, Mabuchi Design Office / Astrobiology Center, Japan.
Several models of Jupiter’s structure that fit data from NASA’s Juno spacecraft suggest that the gas giant has a diluted core, with a total heavy-element mass ranging from ten to a few tens of Earth masses (5-15% of the Jovian mass), and that heavy elements — elements other than hydrogen and helium — are distributed within a region extending to nearly half of Jupiter’s radius.
“This is puzzling. It suggests that something happened that stirred up the core, and that’s where the giant impact comes into play,” said Dr. Andrea Isella, an astronomer at Rice University.
“Leading theories of planet formation suggest Jupiter began as a dense, rocky or icy planet that later gathered its thick atmosphere from the primordial disk of gas and dust that birthed our Sun.”
Impacts at a grazing angle could result in the impacting planet becoming gravitationally trapped and gradually sinking into Jupiter’s core, and smaller planetary embryos about as massive as Earth would disintegrate in Jupiter’s thick atmosphere.
“The only scenario that resulted in a core-density profile similar to what Juno measures today is a head-on impact with a planetary embryo about 10 times more massive than Earth,” said Dr. Shang-Fei Liu, a researcher at Sun Yat-sen University and Rice University.
The team’s calculations suggest that even if this impact happened 4.5 billion years ago, it could still take many, many billions of years for the heavy material to settle back down into a dense core.
“The study’s implications reach beyond our Solar System,” Dr. Isella said.
“There are astronomical observations of stars that might be explained by this kind of event.”
“This is still a new field, so the results are far from solid, but as some people have been looking for planets around distant stars, they sometimes see infrared emissions that disappear after a few years.”
“One idea is that if you are looking at a star as two rocky planets collide head-on and shatter, you could create a cloud of dust that absorbs stellar light and reemits it. So, you kind of see a flash, in the sense that now you have this cloud of dust that emits light. And then after some time, the dust dissipates and that emission goes away.”
The research is published in the journal Nature.
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Shang-Fei Liu et al. 2019. The formation of Jupiter’s diluted core by a giant impact. Nature 572: 355-357; doi: 10.1038/s41586-019-1470-2
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