Uranus is arguably the most mysterious planet in the solar system – we know very little about it. So far, we have only visited the planet once, with the Voyager 2 spacecraft back in 1986. The most obvious odd thing about this ice giant is the fact that it is spinning on its side. Unlike…
Uranus is arguably the most mysterious planet in the solar system – we know very little about it. So far, we have only visited the planet once, with the Voyager 2 spacecraft back in 1986. The most obvious odd thing about this ice giant is the fact that it is spinning on its side.
Unlike all the other planets, which spin roughly “upright” with their spin axes at close to right angles to their orbits around the sun, Uranus is tilted by almost a right angle. So in its summer, the north pole points almost directly towards the sun. And unlike Saturn, Jupiter, and Neptune, which have horizontal sets of rings around them, Uranus has vertical rings and moons that orbit around its tilted equator.
The ice giant also has a surprisingly cold temperature and a messy and off-centre magnetic field, unlike the neat bar-magnet shape of most other planets like Earth or Jupiter. Scientists therefore suspect that Uranus was once similar to the other planets in the solar system but was suddenly flipped over. So what happened? Our new research, published in the Astrophysical Journal and presented at a meeting of the American Geophysical Union, offers a clue.
Our solar system used to be a much more violent place, with protoplanets (bodies developing to become planets) colliding in violent giant impacts that helped create the worlds we see today. Most researchers believe that Uranus’ spin is the consequence of a dramatic collision. We set out to uncover how it could have happened.
We wanted to study giant impacts on Uranus to see exactly how such a collision could have affected the planet’s evolution. Unfortunately, we can’t (yet) build two planets in a lab and smash them together to see what really happens. Instead, we ran computer models simulating the events using a powerful supercomputer as the next best thing.
The basic idea was to model the colliding planets with millions of particles in the computer, each representing a lump of planetary material. We give the simulation the equations that describe how physics like gravity and material pressure work, so it can calculate how the particles evolve with time as they crash into each other.
