lpetrich
Contributor
Planet Uranus is well-known for its high axial tilt, a tilt that makes it seem to roll on its side. It is 97.77d or 82.23d retrograde. Other planets are not quite as tilted. Mercury: 0.03d, Venus 177.36d or 2.64d retrograde, Earth 23.44d, Mars 25.19d, Jupiter 3.13d, Saturn 26.73d, Neptune 28.32d.
Planet-Shifting Collision Shaped Uranus’ “Rolling” Rotation | NASA -- shows a simulation of an off-center collision.
Another possible source is precession-orbit resonances. Not only do planets' spins precess, but also their orbit orientation and pericenter directions. If they do so at close enough frequencies, that can amplify the axial-tilt variation due to orbit-orientation precession.
The Earth is rather far from such a resonance due to its moon -- its obliquity varies by only a degree from average. Mars does not have a big moon, and its obliquity varies by some 10 degrees in the short term (several hundred thousand years) and more than that in the long term (several tens of millions of years and more).
However, the outer-planet obliquities seem to be rather stable.
Planet-Shifting Collision Shaped Uranus’ “Rolling” Rotation | NASA -- shows a simulation of an off-center collision.
Another possible source is precession-orbit resonances. Not only do planets' spins precess, but also their orbit orientation and pericenter directions. If they do so at close enough frequencies, that can amplify the axial-tilt variation due to orbit-orientation precession.
The Earth is rather far from such a resonance due to its moon -- its obliquity varies by only a degree from average. Mars does not have a big moon, and its obliquity varies by some 10 degrees in the short term (several hundred thousand years) and more than that in the long term (several tens of millions of years and more).
However, the outer-planet obliquities seem to be rather stable.