'Cataclysmic' collision shaped Uranus' evolution

July 2, 2018, Durham University
The collision with Uranus of a massive object twice the size of Earth that caused the planet's unusual spin, from a high-resolution simulation using over ten million particles, coloured by their internal energy. Credit: Jacob Kegerreis/Durham University

Uranus was hit by a massive object roughly twice the size of Earth that caused the planet to tilt and could explain its freezing temperatures, according to new research.

Astronomers at Durham University, UK, led an international team of experts to investigate how Uranus came to be tilted on its side and what consequences a giant would have had on the planet's evolution.

The team ran the first high-resolution computer simulations of different massive collisions with the ice giant to try to work out how the planet evolved.

The research confirms a previous study which said that Uranus' tilted position was caused by a with a massive object—most likely a young proto-planet made of rock and ice—during the formation of the solar system about 4 billion years ago.

The simulations also suggested that debris from the impactor could form a thin shell near the edge of the planet's ice layer and trap the heat emanating from Uranus' core. The trapping of this internal heat could in part help explain Uranus' extremely cold temperature of the planet's outer atmosphere (-216 degrees Celsius, -357 degrees Fahrenheit), the researchers said.

The findings are published in The Astrophysical Journal.

A simulation showing a grazing giant impact between a massive object and the young Uranus. Research led by Durham University, UK, confirms that a massive object roughly twice the size of Earth hit Uranus about 4 billion years ago and caused the planet's unusual tilt. The collision could explain Uranus' freezing temperatures. The clock in the top left of the animation shows hours since the start of simulation. Credit: Jacob Kegerreis/Durham University

Lead author Jacob Kegerreis, Ph.D. researcher in Durham University's Institute for Computational Cosmology, said: "Uranus spins on its side, with its axis pointing almost at right angles to those of all the other in the solar system. This was almost certainly caused by a giant impact, but we know very little about how this actually happened and how else such a violent event affected the planet.

"We ran more than 50 different impact scenarios using a high-powered super computer to see if we could recreate the conditions that shaped the planet's evolution.

"Our findings confirm that the most likely outcome was that the young Uranus was involved in a cataclysmic collision with an object twice the mass of Earth, if not larger, knocking it on to its side and setting in process the events that helped create the planet we see today."

There has been a question mark over how Uranus managed to retain its atmosphere when a violent collision might have been expected to send it hurtling into space.

According to the simulations, this can most likely be explained by the impact object striking a grazing blow on the planet. The collision was strong enough to affect Uranus' tilt, but the planet was able to retain the majority of its atmosphere.

A 2004 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.

The research could also help explain the formation of Uranus' rings and moons, with the simulations suggesting the impact could jettison rock and ice into orbit around the planet. This rock and ice could have then clumped together to form the planet's inner satellites and perhaps altered the rotation of any pre-existing moons already orbiting Uranus.

The simulations show that the impact could have created molten ice and lopsided lumps of rock inside the planet. This could help explain Uranus' tilted and off-centre magnetic field.

Uranus is similar to the most common type of exoplanets—planets found outside of our solar system—and the researchers hope their findings will help explain how these planets evolved and understand more about their chemical composition.

Explore further: Study of Uranus suggests some of its moons are on a collision course

More information: Astrophysical Journal (2018). DOI: 10.3847/1538-4357/aac725

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5 / 5 (8) Jul 02, 2018
The unusual coloration and orientation of Uranus is endlessly fascinating.
Mark Thomas
5 / 5 (7) Jul 02, 2018
Uranus is the nearest planet to have never been orbited by a probe from Earth. I would be so awesome to get close up images of Uranus, including its rings and moons, like the kind the Cassini probe returned from Saturn.
3.7 / 5 (3) Jul 02, 2018
Yes, drone probes to Uranus would be very useful if the supposition that many planets in other star systems display predictable patterns of similar collisions. That such events may be quite common among newly forming systems.
2.6 / 5 (5) Jul 02, 2018
Oh stop...you guys are killing me.
1 / 5 (7) Jul 03, 2018
I like the 'series of bumps' argument. Our Vulcan (Planet 9) causes comet swarms to form that would threaten Uranus at the same nominal point in its orbit. They last about a million years before they are destroyed or ejected from our solar system. Every so often Uranus would be bumped by some of these massive Kuiper Belt bodies drawn into 3:2 Resonate orbits (with Vulcan):
A Dangerous New Jovian Sized Body In Our Solar System
A 2 Earth sized collision would almost destroy Uranus leaving many small asteroid like bodies and these are not found in the local regions.
1 / 5 (7) Jul 03, 2018
Most of the time, the comet swarms formed by Vulcan would not affect Uranus. But once there was a major impact, there would be a similar opportunity at every Resonate interval (9938 years). The celestial geometries would 'line up', but Uranus would have to be at the same nominal point in its orbit or it would mot get hit. The swarms seen to be about 5 years long in length judging by the one that threatens earth. But maybe each swarm could be very different.
4.2 / 5 (6) Jul 03, 2018
Cool, and very analogous to how Earth/Moon, Mars/northern plains+moons and Pluto/Charon formed.

@yaridanjo: "Vulcan" was a hypothetical planet inside Mercury orbit; relativity explained Mercury's orbit. Planet Nine is a modern hypothetical, explaining some anomalous Kuiper Belt Object behavior as well as the planetary plan tilt (of 6 degrees).

But Planet Nine orbit is - if it exists - well inside the comet Oort cloud (600 au vs 100,000 au) - and does not affect comets aside from spreading the Oort cloud early on, until its effect was guaranteed nil. No peer review publications using elaborate simulations claim what you without any evidence whatsoever claimed.

Please refrain from spamming irrelevant links. Most readers here are interested in factual nature and science.
1 / 5 (6) Jul 03, 2018
Torbjorn: we have the complete set of orbital parameters and an estimate of mass for our Vulcan in the outer solar system. Two of these seem to be very close to what some astronomers expect for Planet Nine. The Spanish astronomers think it's semi-major axis is in the 300-400 AU range and the UofAz astronomers think its orbital inclination is 18 or 48 degrees.
These are close to what we (and Forbes 1880) found. Madam Blavatsky named this body Vulcan, but she never claimed it was close to the Sun. Astronomers erroneously thought so. The parameter correlation is discussed in the cited link in my previous post if you wish to read it, including several other independent ways to verify its orbital period.
1 / 5 (4) Jul 04, 2018
It is a well-known fact that the Earth's axis was differently lean through history. And not because of cataclysmic collision.
"help explain the formation of Uranus' rings and moons"
Speculations against science. They have also argued that Pluto will have rings, in contrast to empirical science that has consistently respected the laws of physics. http://www.svemir...nd-Pluto
Ring formation is a scientific discipline that does not use speculation. https://www.acade..._objects
not rated yet Jul 04, 2018
"No peer review publications using elaborate simulations claim what you without any evidence whatsoever claimed. "

Putting faith in a simulation as an accurate proxy for reality is fine as long as the simulation is using, for the most part measured variables. I like that they put links under the article to other articles in which different theories are proposed, keeps one from putting too much stock in one where we are missing a planet of twice the earths mass or evidence one was ever here. The trajectory of a "grazing" blow which would cause Uranus to orient this way and where the other body wound up are a couple of key points to ponder.

"Cool, and very analogous to how Earth/Moon, Mars/northern plains+moons and Pluto/Charon formed."

Properly, the article uses the words, "could, suggested, almost certainly, most likely," several times to indicate that this is a theory based on a simulation. The statement above assumes this theory is 100% correct, careful...
1 / 5 (4) Jul 04, 2018
"No peer review publications using elaborate simulations claim what you without any evidence whatsoever claimed. "
How is the 'peer review process' doing so far in finding Planet Nine? Our Vulcan has two of the six orbital parameters that are consistent with what some astronomers are anticipating for Planet Nine. Our Vulcan is in a stable orbite that would not be ejected by a passing star over the lifetime of our solar system. It is not a captured exoplanet:
Our Vulcan explains Ice Ages and past castrophic events:
But let's all just close our eyes because there is no standard 'peer review' which usually are not worth much anyway.
not rated yet Jul 04, 2018
So apparently Uranus took a pounding!
5 / 5 (1) Jul 10, 2018
For everything that science does not know to explain, it invents some phenomena in which they believe, and convict other people in such nonsense. If science believes that the universe was created from nothing (big bang), then it is no wonder that we hear many fatamorgans from "great scientists" like Einstein.
Science does not even know today the true path of heavenly bodies, nor does it know why our Moon always has its own side facing Earth. If this is known, then science would not invent nebulosity and stupidity, because it would understand the structure of the universe and the laws that all things are in the infinite universe. Why Uranus has a retrograde spin like Venus and more planet planners (months).
This can be explained, if this issue of our month is solved.

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