Why do all the planets occupy, more or less, the same orbital plane? The best astronomical conjecture indicates that they move in the same orbital plane because they were born from the same and unique disk of matter that was quite flat.
Theories suggest that the Solar System was originally a huge mass of rotating gas and dust, perhaps spherical at first. Under the influence of his own gravitational attraction was condensing, which had to start spinning faster and faster to preserve the angular momentum.
At a certain point in this process of increasing condensation and rotation, the centrifugal effect eventually broke off a portion of matter from the equatorial plane. This portion of torn matter, which represented a small percentage of the total, formed a large flat disk around the main central portion of the cloud.
In one way or another (because there is not a general consensus on the details) a series of planets were condensed from that disk, while the bulk of the cloud became the Sun. The planets continued to spin on the region previously occupied by the disk, and for that reason they all revolve more or less in the same plane of the solar equator.
For similar reasons, the planets, as they condensed, formed satellites that rotate, usually in a single plane, which coincides with that of the planet's equator.
It is believed that the exceptions to this rule are due to violent events that occurred long after the general formation of the solar system. The planet Pluto rotates in a plane that forms an angle of 17 degrees with the plane of revolution of the Earth. No other planet has such an inclined orbit.
Some astronomers have conjectured that Pluto might once be a satellite of Neptune and that it managed to break free thanks to some undetermined cataclysm. Of the current satellites of Neptune, the main one, which is Triton, does not rotate in the equatorial plane of Neptune, which is another indication of some cataclysm that affected that planet.
Jupiter has seven small and distant satellites that do not rotate in the plane of its equator. The outermost satellite of Saturn is in the same case. It is likely that these satellites did not form in their present position, at the time the solar system was born, but rather they were asteroids captured much later by those giant planets.
Many of the asteroids that rotate between the orbits of Mars and Jupiter have very inclined orbital planes. Once again, everything seems to indicate a catastrophe. It is quite possible that the asteroids were originally a single small planet that rotated in the general plane. Long after the formation of the solar system, an explosion or series of explosions could fragment that evil world, placing the fragments in orbits that, in many cases differed greatly from the general orbital plane.
Comets rotate in all possible planes. Now, there are astronomers who believe that a scattered cloud of comets exists just outside the solar system, about a light-year from the Sun. These comets may have condensed from the outermost portions of the original spherical cloud, before the general contraction begins and before the equatorial disk is formed.
In such circumstances, when occasionally a comet leaves that spherical layer and precipitates into the inner regions of the solar system (perhaps as a result of the gravitational influence of distant stars), its plane of rotation around the Sun can be any.
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