Long before it became the giant planet we know today, Jupiter was even larger and had a significantly stronger magnetic field, according to a recent study that looked back at its early history.
Researchers published their findings on Tuesday (May 20) in the journal Nature Astronomy. Their calculations indicate that just 3.8 million years after the solar system’s first solid objects formed, Jupiter had grown to twice its current size and possessed a magnetic field at least 50 times stronger than it does now.
“We’ve identified exact conditions that future models need to replicate, setting strict limits on when and how Jupiter formed,” said Konstantin Batygin, a planetary science professor at the California Institute of Technology who led the study. “This takes us a step closer to uncovering how not just Jupiter, but the entire solar system, came to be.”
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Tiny Moons Reveal Big Clues About Jupiter’s Early History
To uncover Jupiter’s ancient planetary conditions, Batygin and his team largely bypassed the assumptions of existing planetary formation models, such as the rate at which primordial gas was gathered by young planets. Instead, they focused on two of Jupiter’s lesser-known moons, Amalthea and Thebe.
These small satellites orbit very close to Jupiter and follow slightly tilted paths that helped the scientists trace the past position of Io, Jupiter’s innermost large moon. That, in turn, helped the researchers pinpoint the inner edge of Jupiter’s ancient circumplanetary disk, which was key to determining how fast Jupiter once spun. By applying the principle of conservation of angular momentum, the team reverse-engineered Jupiter’s original size, Batygin told.
“It felt remarkable that two relatively minor moons provided such clear evidence of Jupiter’s early state,” the researcher recalled. “The real excitement was achieving this result independently of complex accretion models that depend on a series of assumptions.”
Jupiter’s Early Growth Offers Key to Solar System’s Formation
Although the study doesn’t directly explore how such a massive Jupiter would have influenced the early solar system, it emphasizes that the planet’s formation and early evolution played a “pivotal role” in shaping the solar system’s overall architecture.
According to Batygin and his team, the new findings also capture Jupiter at a crucial point in time, when the cloud of gas and dust left over from the sun’s formation evaporated. This marked the end of planet formation and locked in the basic layout of the solar system.
“What we’ve established here is a valuable benchmark,” Batygin said in the statement. “A point from which we can more confidently reconstruct the evolution of our solar system.”
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