- A new study suggests that Jupiter was hit by a young planet with 10 times the mass of Earth about 4.5 billion years ago.
- The planet hit Jupiter's core and stirred the heavy elements inside. According to the study, Jupiter absorbed the impacting planet.
- This collision would explain readings from NASA's Jupiter orbiting spacecraft, Juno, which indicates the planet's core is less dense and has more diffuse heavy elements than scientists expected.
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When Jupiter was young, about 4.5 billion years ago, a protoplanet crashed 10 times the mass of Earth's head-on onto its surface.
The impact shook Jupiter to its core – literally.
It is found by a new study by astronomers at Rice University and China's Sun Yat-sen University, which was published last week in the journal Nature.
An ancient collision, the researchers suggest, would explain why Jupiter's core is less dense and more diffuse than the scientists expected.
NASA's Jupiter orbiting spacecraft, Juno, has been gathering information on the internal structure and composition of our solar system's largest planet since it arrived there in July 2016. Two years ago, it sent back some odd gravitational measurements.
Scientists expected heavy elements would be concentrated in the center of Jupiter, leaving an outer "envelope" of light hydrogen and helium around the densest part of the nucleus. Instead, Juno's measurements showed that heavy elements are diffuse throughout the center of Jupiter, in an area up to half the planet's radius.
"This is confusing," Andrea Isella, an astronomer and co-author of the study, said in a press release. "It suggests that something happened that touched the core and that is where the gigantic influence comes into play."
Shang-Fei Liu, who worked as a postdoctoral researcher on Isella's team, was the first to suggest that an early collision could be blamed for spinning Jupiter's core.
"It sounded very unlikely to me," Isella said. "Like a one-in-a-trillion probability. But Shang-Fei convinced me by pure calculation that this was not so unlikely."
Liu is now a faculty member at Sun Yat-sen University and the lead author of the new study.
The violent history of our solar systems
The early history of our solar system was full of giant collisions.
The moon formed after a giant body collided with Earth 4.5 billion years ago, and its craters are the scars of a billion-year bombardment of asteroids. Scientists believe that the significant slopes of the rotating axes of Saturn, Uranus and Neptune could also indicate that the planets were subject to major collisions long ago.
To investigate Jupiter's past, Liu & # 39; s team estimated the probability of different collision scenarios at different angles, running thousands of computer simulations. The team found that the immense mass and gravity of the young Jupiter strongly influenced the "embryos" of nearby planets – bodies made of slowly coalescing dust and debris.
So front-on collisions were more likely than windy blows due to the impact of Jupiter's gravity. In each scenario the team analyzed, there was at least a 40% chance of Jupiter absorbing another planet in its first few million years, the researchers concluded.
"The only scenario that resulted in a nuclear density profile similar to what Juno is measuring today is a front-on impact with a planetary embryo that's about 10 times more massive than Earth," Liu said.
The core of the crashed planet would then be merged with Jupiter's core.
"Because it's close and it comes with a lot of energy, the impacter would be like a bullet going through the atmosphere and hitting the core in the front," Isella said. "Before impact, you have a very dense core surrounded by atmosphere. The main impact is spreading things out and diluting the core."
The impact of the crash on Jupiter kills today
Jupiter's diluted core is probably still recovering from the old crunch.
"It can still take many, many billions of years for the heavy material to settle into a dense core under the circumstances suggested by the paper," Isella said.
Information about these planetary collisions can also help scientists study star systems beyond our own.
Isella is co-investigator in NASA's CLEVER planets team investigating the origin of elements important to life on young rocky plants. The project, he said, has observed spurts of infrared light in distant star systems.
"Since some people have been looking for planets around distant stars, they sometimes see infrared emissions that disappear after a few years," Isella said.
One explanation, he said, could be that these observations show violent collisions that Jupiter experienced. If two rocky planets collide and burst, it could give off a cloud of dust reflecting the nearby star's light. For astronomers' telescopes, it would appear as a light but fleeting flash, as the reflected light would disappear as the dust particles in the cloud flow apart.
Fortunately, however, our own solar system has settled in the 4.5 billion years since Jupiter's major collision.