Orbits in the Solar System

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If the planets in our solar system really condensed from a single cloud of dust(the old-earth theory), why are some of them orbiting in different directions?

Almost all bodies in the Solar System orbit and rotate in the same direction, although several exceptions exist. This predominant direction is called prograde (if you were to look down on the Solar System from the Sun's North Pole, it would be counter-clockwise), and the opposite direction is called retrograde. It is sometimes claimed that, if the Solar System really condensed from a dust cloud as is generally accepted, then all orbits should be prograde without exception.

A closer look shows those bodies that do have retrograde orbits (such as comets and Neptune's moon Triton) show other signs that they are not in their original orbits. These signs include high inclinations and eccentricities (other indicators of irregularity in an orbit), compositions that are different from other nearby bodies, and in some cases (such as Triton), indications of extreme tidal heating due to the body's being forced into a new orbit.

The conclusion from these observations is that these objects were formed elsewhere in the Solar System (presumably with prograde orbits), and then were thrown into their present orbits by later events (See Comets in the Solar System). So the theory that all Solar System bodies were formed with prograde orbits remains intact.(1)

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