Miranda looks like it’s been Frankensteined together. The small, lumpy moon orbits Uranus and has a surface covered by patches of intersecting ridges, weirdly bumpy terrain and pockmarked plains, and dark, irregular canyons. It’s kind of like a badly crafted moon-quilt, except there’s nothing warm and fuzzy about a barren chunk of icy rock with grooves that make the Grand Canyon look like a paper cut.
Earlier this week, I asked a bunch of scientists to share what they’ve been the most surprised by in the solar system. “The absolute weirdness of Miranda,” was one of the responses from planetary scientist Bill Bottke of the Southwest Research Institute. There are a number of bizarre satellites in the solar system, so Bottke pointing to Miranda meant it was worth a closer look.
Miranda was spotted in 1948 by Gerard Kuiper, but it wasn’t until Voyager 2 swung by the solar system’s most unfortunately named planet in 1986 that we got a good look at its little moon. Miranda is only 500 kilometers across, or about one-seventh the size of our moon.
Basically, Miranda appears as though it’s made out of pieces that don’t quite fit together properly, sort of like poor, lurchy Frankenstein. How the moon came to be like this is still a mystery. One theory suggests that in its first incarnation, Miranda was a less-grotesque, more-normal version of itself — until a giant impact or five came along and blew the moon apart. The pieces eventually reassembled, but not in a way that made much sense. Another hypothesis suggests that meteorite impacts locally melted the moon, and slush rising to the surface formed the giant, ridged patches scientists call “coronae.” Other theories have thrown in a little icy volcanism and internal heating caused by gravitational interactions with Uranus and its other moons. Or, Miranda could have begun to differentiate, with its internal layers separating into something like a core, mantle, and crust — but froze before it finished the job.