Frozen, scarred, and utterly mysterious, the Uranian moon of Miranda is one of the strangest objects in our solar system. None of the hundreds of extraterrestrial objects we’ve discovered looks so battle-worn—but the reasons for its tears, patches, and inexplicable surface features are not altogether clear to us yet. Could the same unexplained geological forces that contributed to its patchwork appearance have produced, and perhaps sustained, some form of life?
It would only be a small oversimplification to say that when exobiologists consider possible extraterrestrial habitats in our outer solar system, they are looking primarily for two things: a large amount of underground water ice and enough geological activity to keep it in a liquid state (since simple heat from the Sun won’t melt surface ice at that distance). These characteristics put Enceladus and Europa on the shortlist of possible extraterrestrial habitats, and we can’t completely eliminate either possibility in our study of Miranda.
The water ice is a given; astronomers have long suspected that it makes up as much as half of Miranda’s composition. But is there any ice to be found underneath the surface in a liquid state? The presence of Miranda’s unusual surface characteristics suggests dramatic geological activity of some kind in its past, but one would expect present-tense geological activity to erode these scars and smooth out the planet’s surface, as it has elsewhere in the solar system. So it’s quite possible to read Miranda’s surface features as indicating a lack of geological activity in the present day, and subsequently a cold interior that can’t sustain anything we would recognize as life.
But it’s not an open and shut case. The strongest evidence to be found in favor of some kind of geological activity on Miranda is its proximity to Uranus; as the closest moon of a planet 15 times the size of Earth, it could face strong tidal forces that would both shape the landscape, in the long run, and keep underground water ice in liquid form long enough for life to evolve. It’s a long shot, but as we know for certain of only one planet that contains life (and still haven’t explored its largest possible habitat), exobiology is the study of long shots. Miranda doesn’t belong on the shortlist with Enceladus and Europa, but it is certainly one of our solar system’s possible habitats for extraterrestrial life.