Which planet rotates on its side, causing extreme axial tilt?

Uranus is unique among the planets in our solar system because it has an axial tilt of about 98 degrees, which essentially means it rotates on its side compared to the plane of the solar system. This extreme tilt suggests that Uranus experienced a significant collision or gravitational interaction in its past that altered its orientation. As a result, the planet's poles face the Sun directly during different parts of its orbit, leading to extreme seasonal variations.

In contrast, Earth, Neptune, and Venus have much smaller axial tilts. Earth has an axial tilt of approximately 23.5 degrees, which contributes to the seasons we experience. Neptune tilts at about 28 degrees, while Venus has a tilt of roughly 177 degrees but rotates in the opposite direction to its orbit. These smaller tilts do not lead to the same extreme seasonal effects seen on Uranus. Thus, it is Uranus that stands out for its dramatic axial tilt and the peculiar rotational characteristics that arise from it.