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Today, our solar system boasts four colossal planets. However, in its nascent stages, it may have hosted an additional one or two. (Image credit: Silicon Worlds)Share this article 0Join the conversationFollow usAdd us as a preferred source on GoogleSubscribe to our newsletter
A recent study suggests that something about the orbital paths of our solar system’s eight planets and their numerous moons doesn’t quite align.
Based on research that analyzed over 100 simulations of our cosmic neighborhood’s early development, it’s possible that two extra giant planets once roamed the outer solar system, altering the trajectories of other planets before eventually being expelled into the void between stars.
The early solar system was in a constant state of flux. A significant event known as the giant planet instability may have caused the gas giants—Jupiter, Saturn, Uranus, and Neptune—to shift from their original positions, ending up farther from the sun.
This planetary migration, first theorized in 2005 by French astronomers as part of the “Nice Model,” likely originated from extremely close interactions between the planets and residual planetary material called planetesimals. Furthermore, refinements made in 2011 proposed the existence of a fifth giant planet that, through gravitational encounters with its neighbors, was ultimately ejected from our celestial vicinity.
However, details about this missing planet remain largely unknown. To gain further insight, the new study “methodically examined the impact of close encounters between giant planets on the orbital stability of their accompanying satellites,” Matthew Clement, a research scientist at the Johns Hopkins University Applied Physics Laboratory and the lead author, informed Live Science via email.
Replaying cosmic history
For their examination, the scientists employed computer models simulating the early outer solar system. Each model tracked the paths of the giant planets and a thousand planetesimals over a period of 20 million years.
From a pre-existing collection of 100,000 such models, the researchers selected a smaller group of 122 simulations that exhibited final configurations broadly consistent with the current arrangement of giant planets. Approximately two-fifths of these selected simulations began with five giant planets, while the remainder started with six. The team then “‘replayed’ these sequences of encounters with the giant planets’ satellites included,” Clement stated.
A composite image featuring Jupiter and its four largest satellites. From top to bottom: Io, Europa, Ganymede, and Callisto.
(Image credit: NASA/JPL/DL)
The simulations indicated that the additional giant planet (or planets) jostled among their neighbors before ultimately being expelled from the system. However, the simulations also yielded an unexpected outcome: Jupiter’s moons largely maintained their stability in simulations featuring two extra ice giants, whereas Uranus’ moons remained stable in those with only one additional giant planet. In essence, Jupiter’s and Uranus’ moons appear to have been preserved through separate occurrences— a result the researchers found surprising.
The scientists observed that three of Jupiter’s major moons—Io, Europa, and Ganymede—currently exist in a complex orbital resonance of 1:2:4. This means Io completes four orbits around Jupiter for every two orbits of Europa and one orbit of Ganymede. Such a finely tuned arrangement suggests that Jupiter’s moons have remained largely undisturbed since their formation, thereby supporting the hypothesis of two additional ice giant planets, according to the researchers.
Planet ping-pong
While ricocheting between the gas giants and Uranus, these supplementary planets likely destabilized Uranus’ moons, leading to collisions. Such impacts would have at least partially fractured the moons and vaporized volatile substances like ice, which subsequently accumulated on the fragments. This could potentially explain why Uranus’ moon Miranda contains 50% more ice than the planet’s other moons, the researchers proposed.
However, this is not the sole potential explanation. Two simulations presented a scenario mirroring the present-day solar system, where both Jupiter’s and Uranus’ satellites endured the same instability. In those particular cases, only one extra ice giant planet was involved. Consequently, further simulations will be necessary to determine whether there was one additional ice giant or two, the researchers noted in their study.
Little can be deduced about the now-absent planets, apart from their masses. In the five-giant-planet scenarios, the extra planet possessed a mass comparable to Neptune’s, while in the six-planet cases, the two additional planets had masses between those of Earth and Neptune, classifying them as “super-Earths.”
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“Considering that the masses are not vastly different from Uranus and Neptune, the physical characteristics of these long-lost planets likely resembled those of the ice giants,” co-author Nathan Kaib, a senior scientist at the Planetary Science Institute in Tucson, Arizona, informed Live Science via email.
Although the researchers do not intend to conduct direct research on the fugitive planets, they plan to continue examining Uranus’ moons to identify signs of disruption and to ascertain “the actual consequences of what happens if the satellites do go unstable,” Clement remarked.
The team’s findings were published online on March 25 in the journal Icarus.
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Sourse: www.livescience.com
