How was Uranus found on his side? We discovered

Uranus is probably the most mysterious planet in the solar system – we know very little about it. Until now, we had visited the planet only once, with the Voyager 2 spacecraft in 1986. The most obvious thing about this ice giant is the fact that It turns on itself.

Unlike all the other planets, which turn about "vertically" with their axes of rotation almost perpendicular to their orbits around the sun, Uranus is inclined almost at right angles. Thus, in summer, the North Pole points almost directly to the sun. And unlike Saturn, Jupiter, and Neptune, which are surrounded by horizontal rings, Uranus has vertical rings and moons that revolve around its tilted equator.

The ice giant also has a surprisingly cold temperature and a disordered and eccentric magnetic field, unlike the ordered form of magnetic bars of most other planets like Earth or Jupiter. Scientists suspect that Uranus was once similar to other planets in the solar system, but was suddenly returned. So, what has happened? Our new research, published in the Astrophysical Journal and presented at a meeting of the American Geophysical Union, offers a clue.

Cataclysmic collision

Our solar system was previously 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 the Uranus rotation is the consequence of a dramatic collision. We tried to find out how that could have happened.

We wanted to study the giant impacts on Uranus to see exactly how such a collision could have affected the evolution of the planet. Unfortunately, we can not (yet) build two planets in a lab and break them together to see what's really going on. Instead, we ran computer models simulating events using a powerful supercomputer as the next best thing.

The basic idea was to model the planets colliding with millions of particles in the computer, each representing a block of planetary material. We give simulation equations describing how physics works, such as gravity and the pressure of materials, so that it can calculate how particles change over time when they break. In this way, we can study even incredibly complicated and disordered results of a giant impact. Another advantage of using computer simulations is that we have total control. We can test a wide variety of different impact scenarios and explore the range of possible outcomes.

Our simulations (see above) show that a body at least twice as mbadive as the Earth could easily create the strange tour de force that Uranus has today in projecting itself and by merging with a young planet. For a larger number of collisions, the impacting body material would likely disperse in a thin warm shell near the edge of the Uranus ice sheet under the hydrogen and helium atmosphere.

This could prevent the mixing of materials inside Uranus, trapping the heat of its formation deep inside. It is interesting to note that this idea seems to correspond to the observation that the exterior of Uranus is so cold today. The thermal evolution is very complicated, but it is at least clear how a giant impact can reshape a planet both inside and out.

Super calculations

The research is also exciting from a computer point of view. Just like the size of a telescope, the number of particles in a simulation limits what we can solve and study. However, simply trying to use more particles to allow new discoveries is a major IT challenge, which means it takes a lot of time, even on a powerful computer.

Our latest simulations use more than 100 m of particles, about 100 to 1,000 times more than most other studies. In addition to producing breathtaking images and animations about the impact of this giant impact, it opens up a whole new set of new scientific questions that we can now begin to tackle.

This improvement is due to SWIFT, a new simulation code that we designed to take full advantage of contemporary "supercomputers". These are basically a lot of normal computers connected to each other. Thus, the execution of a large simulation depends on the division of calculations between all parts of the supercomputer.

SWIFT estimates the duration of each calculation task in the simulation and tries to share the job carefully with care for maximum efficiency. Just like a new large telescope, this jump to 1000 times higher resolution reveals details never seen before.

Exoplanets and beyond

In addition to learning more about the specific story of Uranus, another important motivation is understanding the formation of the planet in general. In recent years, we have discovered that the most common type of exoplanets (planets that orbit other stars than our sun) is quite similar to Uranus and Neptune. Thus, everything we learn about the possible evolution of our own ice giants contributes to our understanding of their distant cousins ​​and the evolution of potentially habitable worlds.

An interesting detail that we have studied and that is very relevant to the question of extraterrestrial life is the fate of an atmosphere after a giant impact. Our high-resolution simulations reveal that part of the atmosphere that survives the initial collision can still be eliminated by the violent bulge of the planet. The absence of atmosphere makes a planet much less likely to accommodate life. Here again, mbadive energy input and the addition of materials could also contribute to the creation of useful chemicals for life. Rocky materials from the core of the impacting body can also mix with the outside atmosphere. This means that we can search for certain trace elements that may indicate similar impacts if we observe them in the atmosphere of an exoplanet.

Uranus and giant impacts in general still pose many questions. Even though our simulations are more and more detailed, we still have a lot to learn. So many people are calling for a new mission to Uranus and Neptune to study their strange magnetic fields, their strange families of moons and rings and even just what they are made of.

I would love that to happen. The combination of observations, theoretical models and computer simulations will help us understand not only Uranus, but also the myriad of planets that fill our universe and how they were created.