Ever wonder where the edge of our solar system lies? You have likely assumed it is just beyond Neptune, the furthest planet from our Sun. Yet, according to astrophysicist Susanne Pfalzner of Forschungszentrum Jülich, a stellar flyby may have stretched the boundaries of the solar system even further.
Thousands of objects with eccentric orbits
"Several thousand celestial bodies are known to move beyond the orbit of Neptune," said Pfalzner. "Surprisingly, many of these so-called trans-Neptunian objects move on eccentric orbits that are inclined relative to the common orbital plane of the planets in the solar system.“
But why do they behave like this? Pfalzner, along with her student Amith Govind and Simon Portegies Zwart from Leiden University , may have found the answer.
The researchers noted that some force must have lifted these trans-Neptunian objects (TNOs) from the disk where they formed and altered their orbits .
"One popular hypothesis is that the planets originally were in a more compact configuration; the TNOs formed between them and were scattered outwards when the planets moved to their current locations," wrote the study authors. "Here, we build on a completely different hypothesis for the TNOs’ origin."
Blame it on the star flyby
The trio conducted over 3,000 computer simulations to test a captivating theory: what if another star caused these peculiar orbits? They found that a close flyby of another star can indeed explain why these TNOs move the way they do.
This hypothetical star could even be responsible for the bizarre orbits of specific TNOs like the dwarf planet Sedna, discovered in 2003, and those that move almost perpendicular to the planet's orbits, such as 2008 KV42 and 2011 KT19.
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"The best match for today's outer solar system is a star slightly lighter than our Sun - about 0.8 solar masses," noted Govind.
"This star passed our Sun at a distance of around 16.5 billion kilometers - about 110 times the distance between the Earth and the Sun, or just under four times the distance to Neptune."
The influence of close star flybys
The findings not only shed light on the motion of trans-Neptunian objects but also open avenues for future astronomical research.
Understanding the influence of close stellar flybys may help astronomers refine their models of solar system formation and dynamics.
Furthermore, the research prompts the question of whether other stellar encounters have similarly shaped the orbits of celestial bodies within our solar system and beyond.
As we continue to explore the mysteries of the outer solar system , we are reminded that our local cosmic landscape is both rich and varied. The existence of numerous TNOs, including intriguing objects like the enigmatic Eris and Haumea, illustrates the complex gravitational dance that defines this region.
Ripple effects closer to home
In a twist, the team discovered that the star's flyby could explain additional mysteries within our solar system.
In their simulations, some trans-Neptunian objects got flung toward the inner solar system, right into the domain of the outer gas giants - Jupiter, Saturn, Uranus, and Neptune.
"Some of these objects could have been captured by the giant planets as moons," said Portegies Zwart. "This would explain why the outer planets of our solar system have two different types of moons."
While regular moons orbit close to planets on circular orbits, irregular moons orbit their planets at a greater distance on inclined, elongated orbits. The research provides the first possible explanation for this intriguing phenomenon.
Solving the mysteries of our solar system
The seemingly straightforward model may hold answers to additional questions as well. "The beauty of this model lies in its simplicity. It answers several open questions about our solar system with just a single cause," said Susanne Pfalzner.
So, perhaps it's time to revisit our view of the solar system's boundaries and consider the impact of a close flyby star from billions of years ago. Ultimately, the research suggests that these types of interstellar interactions may be pivotal in the evolution of planetary systems.
The study is published in the journal Nature Astronomy .
Video Credit: Forschungszentrum Jülich
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