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The planet Uranus is another solar system anomaly, where according to the NASA profile has an axial tilt of 97.8 degrees, also considered to be retrograde. This NASA summary "Uranus" suggests the current theory of a large planet-sized impact earlier in its history.

Does the planet-impact theory still hold true or have new accepted theories come to light?

Most of all, are there any results from any simulations available?

A note, this is posted as a separate question to my other question "What is the current accepted theory as to why Venus has a slow retrograde rotation?" as the axial tilt is significantly different.

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up vote 8 down vote accepted

Nasa.gov speculates that "It is possible that an Earth-sized object crashed into Uranus and caused Uranus to rotate on its side."

A recent test by Space.com suggests that "Planet Uranus Got Sideways Tilt From Multiple Impacts".

They found that a series of at least two smaller collisions can explain the moons' motions much better than a single giant impact, researchers said. The early solar system thus may have been a more volatile and violent place than previously thought, they added.

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