Evidence

The observed natural tendency for binary (occurs when two objects orbit around a point that lies in between them) Kuiper Belt objects (KBO) and their properties can be a natural consequence of KBO formation by gravitational instability.

Gravitational collapse (GC) occurs when large objects rapidly form in the protoplanetary disk and collapse under their own gravity. GC that occurred during our solar system’s growth most likely caused the formation of Kuiper Belt (KB) binaries. An example of KB binaries are the interactions between Pluto and Charon. Most of the classical cold KB objects (KBOs) are binaries. Understanding how much an orbit is tilted compares to the plane of the elliptic, or an object’s inclination, can give clues to how the object formed. Knowing the inclination distribution of KBO binaries can help constrain KBO formation. Studying inclination and other properties of KBO binaries can lead to a better understanding about the physical conditions that existed in the trans-Neptunian disk when large KBOs formed. This is important because KB binaries are thought to be remnants from the earliest days of our solar system. This means that planetary migration might not have formed the Kuiper Belt.

Authors

Nesvorny, D., Youdin, A. N., and Richardson, D. C.

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Evidence

The solar system spread to its current size during the growth and dynamical evolution of the ice giants, and planetary ejections, which are thought to have populated the Kuiper Belt, are very rare.

Recently the theory that very massive planets with unstable orbits must have ejected planetesimals out to the Kuiper Belt and the Oort Cloud was proposed. This has since been refuted through a series of simulations that were done to test this theory. It was found that this theory leads to a planet to be in orbit far beyond the current orbit of Neptune. Also, it was found that Uranus and Neptune would not be able to grow to their current size if this theory were true. This simulation suggests that planetary migration must not have played a part in forming the Kuiper Belt and the Oort Cloud.

Authors

Levinson, H. F. and Morbidelli, A.

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Evidence

Simulations of the Nice Model have proven that it is not an accurate migration theory.

The Nice Model explains the origin of the late heavy bombardment in the inner solar system, the existence of the trojans around Jupiter and around Neptune, and the orbits of the giant planets.1 Because of the late heavy bombardment that occurs in the Nice Model, about 99.999% of the asteroids are destroyed in catastrophic collisions before they join the Oort cloud. This happens because these bodies originated in the inner solar system where they collisionally evolve for about ten million years. Nice Model simulations only produce about 0.1% of the Oort Cloud asteroids that are observed today. These simulations demonstrate that the Nice Model cannot explain how or why the objects on our solar system have stable orbits.

Authors

Shannon, A., Jackson, A. P., and Wyatt, M. C. (

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Evidence

The Sun captured comets that now make up its Oort Cloud from other stars while it was still in its initial formation period.

Sun growth simulations have produced two possible ways that the Oort Cloud most likely formed. The first is that the comets were randomly captured during possible close encounters with other nearby stars. They would have been captured because their velocities would have matched that of their new parent star. The second, and rarer, way was through direct encounters with another star that would have been about half the mass of our Sun. Due to the mass difference, the comets would have been affected by the large gravitational pull of our Sun. It has been concluded that over 90% of the observed Oort Cloud comets and rocky material have an extrasolar origin. This suggests that planetary migration did not help form the Oort Cloud.

Authors

Levinson, H. F., Duncan, M. J., Brasser, R., and Kaufmann, D. E.

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Evidence

The Sun’s original galactocentric distance, which was much closer to the center of the Milky Way Galaxy, and its associated stronger gravity might have caused Oort cloud bodies to be stripped or cycled back into the planetary region, closer to the Sun.

In a recent simulation of the Milky Way Galaxy, some stars were studied based on their solar-like ages, their position in the Galaxy, and their kinematics. It was found that the position of these stars in the Galaxy have varied dramatically during their growth and seem to have many different orbital histories possible for stars like our Sun. 90337 Sedna, thought to be an asteroid or a possible dwarf planet, was discovered in the Oort Cloud and it has the second longest orbital period in our solar system. It is believed to have a similar composition to Kuiper Belt objects (KBOs), but it is located in the inner edge of the Oort Cloud. Out of the multiple runs of the simulation, only about 30% generated asteroids with an orbit like Sedna’s. So, Sedna’s orbital dynamics could be a clue to understanding the Sun’s history in the Milky Way. This simulation demonstrates that as our Sun migrated through the Galaxy it effected the orbits and locations of objects in the solar system.

Authors

Kaib, N. A., Roškar, R., and Quinn, T.

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