Here's why:

* Uranus: Its axial tilt is a whopping 97.77 degrees, which means it essentially spins on its side. This extreme tilt is believed to be the result of a collision with a massive object early in its history.

The other Jovian planets have much smaller tilts:

* Jupiter: 3.13 degrees

* Saturn: 26.73 degrees

* Neptune: 28.32 degrees