Uranus has a sideways tilt together with its 27 known moons compared to the plane of the Solar System. A new modeling strategy explains why.
Uranus orbits the Sun on the same plane as the rest of the planets in the Solar System. Unlike the rest, however, Uranus is tilted more than 90 degrees compared to that plane. And so are the gaseous planet’s ring system and the orbits of its 27 known moons.
The research, published in Nature Astronomy, reveals a huge cosmic crash might have led to the strange behaviors observed from the ice giant.
The new model suggests “a small icy planet – roughly 1-3 times the mass of the Earth,” knocked Uranus on its side shortly after it formed.
The collision also apparently altered the planet’s rotation. Uranus spins around its axis once every 17 hours, significantly faster than Earth does.
Giant impacts in the cold and dark outer solar system have different consequences than smashups much closer to the sun, such as the ancient collision that resulted in the formation of Earth’s moon, the researchers found.
About 4.5 billion years ago a Mars-sized body called Theia likely crashed into Earth and cracked off our planet. Debris from the impact coalesced into a single mass and gave rise to our Moon.
But the material released during the Uranus collision was much more volatile and remained gaseous longer. The proto-Uranus gobbled most of this gas up, leaving less of it around to form moons.
“This model is the first to explain the configuration of Uranus’ moon system, and it may help explain the configurations of other icy planets in our solar system such as Neptune,” study lead author Shigeru Ida, of the Earth-Life Science Institute at the Tokyo Institute of Technology in Japan, said in a statement.