Uranus, the Sideways Planet

Why We Study Uranus

There’s no getting around it: for English speakers, Uranus is the butt of all planet jokes. But there’s much more to this world than potty humor. Like its cousin Neptune, Uranus has only been visited by one spacecraft. Yet most of the planets we’ve found around other stars are Uranus and Neptune-sized, so learning this mysterious world teaches us about other solar systems and whether our own is unique.

Uniquely among our planets, Uranus and the orbits of its rings and moons float through space sideways. How this happened isn’t known for sure. Another large world could have crashed into the planet long ago, or a larger, previous ring system could have caused Uranus to wobble and tip over. Figuring out what happened would give scientists important insights into how planets evolve.

Uranus’ atmosphere is mostly hydrogen and helium like Jupiter and Saturn, with traces of methane that absorb red light and give the planet its cyan appearance. Beneath the atmosphere is an exotic slush of partially frozen water, ammonia, and methane. For this reason we call Uranus an ice giant, even though the ice isn’t like anything you’d put in your drink: super-compressed ice can reach temperatures of thousands of degrees!

Uranus lies 20 times further from the sun than Earth. At this distance, the disk of gas and dust that formed our solar system 4.5 billion years ago was probably too thin to form Uranus. Like Neptune, Uranus was probably born closer to the sun before migrating outward. Piecing together what happened would tell us what the early solar system was like before life arose on Earth.

Uranus’ five largest moons in order of ascending size are Miranda, Ariel, Umbriel, Oberon, and Titania. The latter two may be warmed enough by gravitational tugs from Uranus and other moons to create liquid water beneath their surfaces. Investigating this possibility would help us learn about the possibilities for life far outside the habitable zone, the not-too-hot, not-too-cold region around stars where liquid can exist on planetary surfaces.