Sunday, August 22, 2021

How Uranus and Neptune swapped their position?

In this article we will discuss how Uranus and Neptune swapped their position? How some small scattered bodies from Kuiper belt caused this migration of planets? We will discuss the effect of Jupiter’s huge mass on the migration of these two outermost planets of solar system? and many more things. So let us start.

The early solar system before the planetary migration consisted of the eight planets where Uranus and Neptune were in opposite locations as compared to their present location. The outer planets were more compact and much closely spaced than in present days. The planets then migrated until they reached their current location. But how did they migrated from their position and what actually happened during the migration? Let us have a look.[Read – Main asteroid belt-an overview]

To better understand the migration of outer planets many models have been proposed till now. Among such model, Nice model is the most promising and accepted model to explain the migration of outer planets. This model was developed by Rodney Gomes, Hal Levinson, Alessandro Morbidelli and Kleomenis Tsiganis.

According to this model the four giant planets i.e. Jupiter, Saturn, Uranus and Neptune were originally found on near-circular orbits between about 5.5 and 17 AU. As of now, their orbits lie between 5.2 and 30 AU. A large, dense disk of small, rock and ice planetesimals also known as the proto-Kuiper belt, extended from the orbit of the outermost giant planet to about 35 AU.[Read – Planet X – why astronomers believe that there exists a planet beyond Pluto?]


The small bodies at the inner edge of proto-Kuiper belt occasionally passed through gravitational encounters with the outermost giant planet, which eventually changed these small bodies’ orbits. And due to this, these small bodies were scattered inwards towards the inner solar system. Due to the inward scattering of small bodies, an exchange of angular momentum took placed which eventually pushed the outermost planet slightly outwards.


After that the inwards moving objects came closer to the gravitational influence of the next gas giants, and this process repeated and the planetesimal were further scattered inwards. ==Slowly slowly not only the small bodies were moving inwards, but the gas giants were also changing their orbits to farther distances from the Sun.

Yes yes you are thinking right that how much puch will some small scattered body apply on these gas gaints. Of course the push these gas giants received while interacting with the small bodies was very small and almost negligible. But, the combined effect of encounters with many small bodies shifted the orbits of these gas giants significantly over time.

But this process came to an end when these small bodies encountered the most massive planet in our solar system i.e. Jupiter. Due to the enormous mass of Jupiter, small scattered bodies were forced to move on highly eccentric orbits and Jupiter even kicked many of them out of the solar system. Due to the conservation of momentum, Jupiter very slowly moved inwards, by scattering the small bodies outwards.

After 500 to 600 million years of slow but gradual migration, Jupiter and Saturn reached their 1:2 mean motion resonance which eventually increased their respective orbital eccentricities. This strong resonance caused a destabilization of the entire solar system, due to which Jupiter pushed Saturn to its current location.


Also due to mutual interaction of Jupiter with the two ice giants, Uranus and Neptune, the two ice giants ended up with by far more eccentric orbits and finally they swap positions making Neptune the outermost planet of our solar system.

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