One of the most enduring mysteries of the Solar System may be a step closer to being solved.
It is well known that Uranus is an oddball, orbiting around the sun on its side, but little is known about how the huge planet came to be this way.
Although the general consensus is that Uranus was involved in some kind of cosmic hit-and-run, two researchers from Paris think the gas giant may have gradually wobbled over millions of years, eventually tipping due to the presence of a large moon.
Usually the planets orbit the sun upright, with the axis of rotation perpendicular to the solar system's plane (i.e. in relation to Earth, pointing "north"). That is, apart from Venus and Uranus. Venus, however, is a more extreme case where the entire planet was turned upside down causing it to rotate in an opposite fashion to Earth.
Uranus is tilted 97 degrees to the vertical. The Earth's tilt is a little over 23 degrees, and it is this tilt that gives our planet seasons. Needless to say, the seasons on Uranus are a little more extreme than ours; each Uranian hemisphere experiences 42 years of continuous sunlight (a year on Uranus is 84 Earth years).