A massive head-on collision between Jupiter and a still-forming planet roughly 4.5 billion years ago may be to blame for puzzling gravitational readings from NASA’s Juno spacecraft, according to a new study.
Astronomers from Rice University and Sun Yat-sen University in China say this startling impact scenario could explain surprising readings on the Gas Giant’s gravitational field, which suggest that Jupiter’s core is more extended and less dense than expected, said a Rice University press release. The team detailed their findings in a study published in Nature on Aug. 14.
“This is puzzling,” said Rice astronomer and study co-author Andrea Isella. “It suggests that something happened that stirred up the core, and that’s where the giant impact comes into play.”
According to Isella, leading planet formation theories suggest that the Gas Giant started off as a dense, rock, or icy planet that later on collected its thick atmosphere from the primordial disk of dust and gas that gave birth to the sun.
At first, Isella was skeptical when lead study author Shang-Fei Liu suggested the possibility that the confusing data could be explained by a colossal impact that changed Jupiter’s core, mixing its core’s dense contents with less dense layers above. However, something changed his mind when Liu showed that the collision scenario may have played a role in the puzzling readings.
“It sounded very unlikely to me,” Isella explained. “Like a one-in-a-trillion probability. But Shang-Fei [Liu] convinced me, by shear calculation, that this was not so improbable.”
The research team ran thousands of computer simulations and discovered that a fast-growing Jupiter may have unsettled the orbits of neighboring “planetary embryos,” protoplanets that were in early planet formation stages. According to Liu, these calculations included estimates of the probability of collisions happening under different situations and distribution of impact angles.
In all cases, the team determined there was at least a 40 percent chance that Jupiter would “gobble up” a planetary embryo within its first few million years. According to the study, the Gas Giant also mass-produced “strong gravitational focusing,” making head-on collisions more common. Furthermore, Liu ran 3D computer models that showed how a head-on collision would impact Jupiter’s core.
“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,” Isella added. “Before impact, you have a very dense core, surrounded by atmosphere. The head-on impact spreads things out, diluting the core.”
According to Liu, smaller planetary embryos about as big as Earth would break apart in Jupiter’s thick atmosphere. Collisions at a grazing angle may result in the impacting planet becoming gravitationally stuck and slowly sinking into the Gas Giant’s core.
“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,” Liu explained.
Even though calculations suggest that the collision occurred about 4.5 billion years ago, it could take billions of years for Jupiter’s core to recover from this major event.
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