A Passing Star May Have Shaped Our Solar System's Odd Moons
Recent research suggests that a passing star might have shaped the strange moons of giant planets like Jupiter and Saturn, reports Live Science. This notion implies that a solitary stellar traveler could have significantly influenced how these moons came to exist in our time.
The study brings forth a bold model that challenges previously held assumptions about solar system evolution. It suggests that over three-quarters of the moons could trace their origins to this celestial encounter.
Moons of the Giant Planets
The giant planets are known for their extensive moons. Saturn currently has 146 moons, with Jupiter following closely behind at 95. Many of these moons share similarities with Earth's own moon. They typically orbit their parent planets in alignment with the rotation of those planets. These moons, designated as regular moons, exhibit nearly circular orbits that align with the planets' equators.
However, not all moons fit this pattern. Saturn's moon Phoebe presents a striking example. It follows an oval-shaped, tilted orbit contrary to Saturn’s rotation — a phenomenon labeled as retrograde motion. Oddly, the solar system has three irregular moons for every regular moon, like Phoebe.
Previous Theories and Current Findings
Previous theories linked the broader presence of irregular moons to Neptune's dynamic movement. William Bottke of the Southwest Research Institute asserted that Neptune played a pivotal role by migrating through a precursor of the Kuiper Belt. This chain of events likely destabilized the rocky bodies in the area, leading many to venture near the giant planets. Through gravity, some bodies could be captured by these planets.
Even so, this interpretation struggles to clarify all facets of the irregular moons — exemplified by their peculiar reddish hues. A newly published study in The Astrophysical Journal Letters offers an alternative theory that a passing star introduced these moons into their current orbits.
The Role of a Visiting Star
The study's lead author, Susanne Pfalzner of Jülich Supercomputing Center, was motivated by prior research indicating that a stellar flyby might have influenced Kuiper Belt objects (KBOs). To investigate, Pfalzner and her team simulated a star's approach to the early solar system. This star, modelled to possess about four-fifths of the sun’s current mass, made a close encounter at around 110 Earth-sun distances.
Through their simulations, the researchers analyzed the gravitational influence of both the sun and the visiting star on thousands of KBOs. They monitored how these trajectories altered over a century.
The findings indicated that a star passing at a 70-degree angle to the ecliptic plane likely redirected 7% of KBOs into elongated orbits near the giant planets. Many of these objects, particularly those drawn near Jupiter and Saturn, exhibited retrograde motion or rarity in being very red — characteristics that define today’s irregular moons.
The simulations indicated that roughly 85% of the KBOs eventually exited the solar system. The remaining KBOs contributed to the formation of irregular moons.
Competing Perspectives
The results were unexpected, according to Pfalzner. This new model offers clear and straightforward explanations about irregular moons and KBO interactions in the solar system. Moreover, stellar encounters are frequent events — primarily involving around 140 million stars within the Milky Way.
However, not all experts are on board with these conclusions. Bottke, who did not take part in this recent study, highlighted that such an exceptionally close pass seems improbable based on statistical analysis. He also pointed out that any significant stellar encounter would likely disrupt the current orbits of the giant planets, effects that should be observable today.
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