Uranus’ odd tilt possibly explained by new model

Tokyo Institute of Technology researchers have published a model that seems to explain Uranus’ bizarre tilt – a collision between a young Uranus and a massive ice world that could have both tipped Uranus over, and also formed its rings and its 27 moons in the process.

Links

Uranus: The Ringed Planet That Sits on its Side

• Uranus: The Ringed Planet That Sits on its Side (Space.com)

Transcript

This is the Daily Space for today, Monday, April 6, 2020.

Welcome to the Daily Space, I am your host, Dr Pamela Gay, and I am here to put science in your brain. Most Mondays through Fridays either I or my co-host Annie Wilson will be here, bringing you a quick run down of all that is new in space and astronomy.

As the effects of the Coronavirus percolate through all of our societies, we’re going to see a tapering off of research as papers already in the queue for publication all get published, but with fewer and fewer associated press releases because universities are shut down. We will also see fewer and fewer papers getting submitted for publication, reviewed, and published as people involved in every step are limited in what they can accomplish by these trying times we live in.

A lot of people have been talking about how Newton was able to go into seclusion during the black plague and come out with heaps of new research accomplished – talking about how it was his most productive time. Well, Newton had 3 things we don’t. 1) There was no internet to distract him with pages of news reports and a myriad of Zoom meetings to fill his day. 2) He had a staff to cook, clean, and risk their lives finding the stuff needed to get by. And 3) He didn’t make the same kinds of social connections so many people need so he wasn’t distracted by loneliness or worry for others. While there are folks out there using this time to perfect their hobbies and advance their work, there are also a lot of folks sitting on their sofa, binge eating whatever snack food was left on the shelf at their grocery store, while binge watching Tiger King and playing Animal Crossing. If that’s what you need to get through your day – that’s ok. There are others struggling to balance their work-from-home job and child care, and everything is  a struggle. That’s reality. We aren’t all Newton. Some of us notice that we’re lying in the gutter looking at the stars, and the smell of the shit around us just makes it hard to get work done. 

As the news continues to taper out, we’re going to work to bring scientists on stream to talk about their work. This week, we will have Stuart Robbins joining us tomorrow to talk about his recent work doing a consistent analysis of Mars changing colors. On Thursday Greg Gbur will join us to talk about gravity, cats, and the intersectional physics of the two. 

For today though, it seems like we might as well talk about Uranus.

In new research coming out of the Tokyo Institute of Technology, researchers have published a model that seems to explain Uranus’ bizarre tilt. This 7th planet from the Sun is knocked on its side, with its rotational pole sitting in the plane of the planets and periodically pointing at the Sun. This is not normal. This is not how planets form. To get into this weird inclination, something had to happen to Uranus. Since this pale blue planet is a swirling mass of gas, we can’t directly see scars left by impacts the same way we can on solid worlds like the Moon or Mars. What Uranus has instead are a set of icy rings and icy moons… and a weirdo tilt.

In their new model, scientists led by Sigeru Ida describe how a collision between a young Uranus and a massive ice world could have both tipped Uranus over and also formed its rings and its 27 moons in the process. The colliding body would have needed to be 1-3 Earth Masses in size, which is larger than any icy body so far found, but is consistent with the kind of world we expect to find out on the edge of the Kuiper Belt, as planet 9. 

While this process was similar in many ways to what happened with our moon, the differences between a rocky impactor and an icy impactor left their marks. The press release explained this so well, we’re just going to quote it: 

“Because the temperature at which water ice forms is low, the impact debris from Uranus and its icy impactor would have mostly vapourised during the collision. This may have also been true for the rocky material involved in Earth’s Moon-forming impact, but in contrast this rocky material had a very high condensation temperature, meaning it solidified quickly, and thus Earth’s Moon was able to collect a significant amount of the debris created by the collision due to its own gravity. In the case of Uranus, a large icy impactor was able to tilt the planet, give it a rapid rotation period (Uranus’ ‘day’ is presently about 17 hours, even faster than Earth’s), and the leftover material from the collision remained gaseous longer. The largest mass body, what would become Uranus, then collected most of the leftovers, and thus Uranus’ present moons are small. To be precise, the ratio of Uranus’ mass to Uranus’ moons’ masses is greater than the ratio of Earth’s mass to its moon by a factor of more than a hundred. Ida and colleagues’ model beautifully reproduces the current configuration of Uranus’ satellites.”

In retrospect, the Earth got kind of lucky in how we got knocked around. We could have ended up as tilted as Uranus, which would have made our seasons much more severe and made the kind of ecosystem we enjoy impossible. As it is, we have a nice tilt that gives us reasonable seasons and a giant moon that gives us a small bit of stability in this crazy universe.

And that rounds out our show for the day.

<———————>

As part of helping keep us all occupied in these really weird times, we’re going to be hosting a lot of additional content on our Twitch channel, and we want to remind you that CosmoQuest has an active community on Discord where you can talk science, volunteer for various projects,  and even find other people to join you in playing some online games. You can find links to everything that is going on at CosmoQuest.org.

Thank you all for listening. Today’s script was written by Pamela Gay, and the Daily Space is produced by Susie Murph. The Daily Space is a product of the Planetary Science Institute, a 501(c)3 non profit dedicated to exploring our Solar System and beyond. We are here thanks to the generous contributions of people like you. The best way you can support us is through Patreon.com/cosmoquestx  Like us? Please share us! You never know whose life you can change by adding a daily dose of science.