Study: A massive object may have struck Uranus, tilting it and ejecting material
A new study suggests that the ice giants Neptune and Uranus may have had catastrophic impacts in the past, resulting in why they look so different from one another, despite having similar mass and size.
As Erika Carlson writes in Discover Magazine:
... [A] team of researchers has used computer simulations to show that collisions with large, rocky bodies could have led to the two planets’ diverging histories, possibly explaining why they look so different.
Perhaps the most obvious difference between the ice giants is their rotation angles. The spin of the planet Uranus is tilted by about 98 degrees compared to its orbital plane. Meanwhile, Neptune and most of the solar system's other planets have rotations that are more or less aligned with their orbits (though Venus likewise rotates the "wrong" way).
Past studies have suggested that giant impacts might explain the tilted spin of Uranus, while also accounting for other differences between the ice giants. So Christian Reinhardt of the University of Zurich and other researchers decided to test whether today’s state-of-the-art 3D simulations would support these ideas.
Uranus*. Image credit:* NASA Goddard
The study explains that, according to their simulations, a large impact "could mix the interior" of Neptune, leading to an "adiabatic temperature profile". A large, dense object could have penetrated to the center of Neptune, "leading to a less centrally concentrated interior".
Neptune. Image credit: NASA/JPL
For Uranus, the authors explain that their simulations suggest that an oblique impact could tilt Uranus and result in enough material being ejected from Uranus "to create a disk where the regular satellites are formed". The authors go on to state that this could explain the formation of Uranus' natural satellites.
Cover image: An infrared composite image of the two hemispheres of Uranus obtained with Keck Telescope adaptive optics. Credit: Lawrence Sromovsky, University of Wisconsin-Madison/W.W. Keck Observatory