Jupiter's anomalous size and location in our Solar System has been puzzling researchers for years, since it does not fit our understanding of planet formation. Now, astronomers think they've figured out how the gas giant has ended up in its curious position
According to current models, giant planets form in the outermost reach of a system, migrate inwards, and end up very close to their star. Not Jupiter, though: a huge planet more than twice as massive as the rest of the Solar System planets combined, but orbiting pretty much in the thick of it
The new research appears to have demystified Jupiter's history. According to computer simulations, the gas giant formed around four times farther out than its current location, just inside Uranus' current orbit, and slowly spiraling its way inwards over the course of 700,000 years
"This is the first time we have proof that Jupiter was formed a long way from the Sun and then migrated to its current orbit, "said astronomer Simona Pirani of Lund University in Sweden
The research was based on asteroids called Trojans. These share Jupiter's orbit;
But there's a conundrum. "The asymmetry has always been a mystery in the Solar System," said astronomer Anders Johansen of Lund University
So the team ran simulations of Jupiter's formation to figure out what might have caused such a strange imbalance
They tested a variety of timeframes and even an outward migration patterns, and found that the scenario that results in Trojan populations
Within two to three million years, it would have migrated inwards to its current position of 5.2 astronomical units. This took roughly 700,000 years.
As it began this spiraling journey closer and closer to the Sun, drawn along by the gravitational force of gases lingering in the Solar System, the baby planet gravitationally picked up the Trojans, with more in the lead group than the trailing group
This occurred before the planetesimal had accreted its gas; at that point, it was still accreting the rock that would collapse to form the planet's core, so it's also likely that Jupiter's core is made up of similar chunks of rock to that found in Trojans, the researchers said.
Where Jupiter formed has been a problem that has long vexed planet scientists, since it seems like gas giants can not form close to a star. The intense gravity, stellar radiation (including heat) and powerful stellar winds in close quarters would prevent the gas from staying together long enough to coalesce into a planet
So, while this contradicts previous research predicated on the formation of Jupiter near the Sun, followed by an outward migration, it also offers a solution – bringing Jupiter into line with what we understand based on observations of other planetary systems
And, of course, if the team's simulations are correct, the asteroids could be "
" We can learn a lot about Jupiter's core and formation from studying the Trojans, "said Johansen.
NASA plans to launch a probe called Lucy's study them in October 2021, so we will not have to wait long to find out
The research has been accepted into Astronomy & Astrophysics and can be read on arXiv