Did Something Massive Smash Into Uranus?

By Ryan F. Mandelbaum on at

You might be aware of one of Uranus’ complexities: It spins on its side, and its moons orbit on that same rotated plane. New evidence strengthens the case that Uranus was smashed in a giant collision, resulting in its sideways orientation to its orbital plane and perhaps explaining some of the planet’s other mysteries.

A new paper performs a series of simulations on Uranus early in its history, taking note of what an early impact may have done to its rotation rate, atmosphere, and internal structure. The impact could have left a clear signature still visible inside the planet we see today.

Uranus really is strange. Not only does it rotate on an axis that sits at a 98-degree angle to its orbital plane, but, unlike the other giant planets, it doesn’t appear to release more heat than it receives from the Sun. Its magnetic field, too, appears warped compared to the Earth’s. An impact could perhaps help explain some of these strange traits.

Scientists have been simulating giant impacts into Uranus since the early 1990s, according to the new paper published in the Astrophysical Journal. This time around, researchers built a new simulation with the newest and best available data of the planet’s composition. This allowed them to model how a giant impactor, perhaps one to three times the mass of Earth, would have deposited “material and energy inside Uranus” and how much debris would be left over, from which moons could form.

“This study provides some great new insights into what might have happened all those billions of years ago, with material left over from the impact possibly even serving to trap some of that heat inside,” Leigh Fletcher, Royal Society Research Fellow at the University of Leicester, told Gizmodo.

But this is just a simulation, and like we always say: All models are flawed, but some are interesting. Models can’t tell us exactly what happened; it will take a lot more data to fully understand Uranus’ story. “Of course, what we really need next is an ambitious robotic mission to explore Uranus and its diverse satellite system,” said Fletcher. “Gravitational, atmospheric, and magnetic field mapping, following what we’ve done at Jupiter with Juno, and at Saturn with Cassini, could provide some new clues to better constrain these models, by unlocking the secrets of an ice giant interior for the first time.”

Uranus is truly a mystery. Will humans finally take up the task to explore it? [ApJ]

Featured image: ESA/Hubble