The Frankenstein Moon: A Patchwork Like No Other
When Voyager 2 flew past Uranus in January 1986, it delivered a surprise: one of its moons looked like a hodgepodge of tectonic scars, cliffs, ridges, craters, and bizarre “patchwork” terrain. That moon is Miranda — small, icy, and yet one of the most geologically diverse surfaces known. Because its terrain appears so disjointed — like stitched-together fragments of different landscapes — scientists sometimes call it a “Frankenstein moon.”
Miranda is the innermost of Uranus’s large moons, small in size (about 470 km across) and composed of mixtures of water ice and rock. Under its tenuous gravity, features grow and persist in striking relief. Its orbit is also unusually inclined compared to Uranus’s equatorial plane, hinting at a tumultuous orbital past.
Topographic Extremes: Cliffs, Coronæ, and Terrains
Verona Rupes: The Titanic Cliff
One standout feature is Verona Rupes, possibly the tallest cliff in the Solar System. Estimates suggest it drops some 20 km (12+ miles) in places — unimaginable heights on Earth. Given Miranda’s low gravity (only about 1% of Earth’s), a fall from its rim might take many minutes.
Coronae: The Puzzle Patches
Miranda hosts three major coronae — Arden, Elsinore, and Inverness. These are oval, “crown-shaped” tectonic or uplifted regions, often with concentric ridges, faults, grooves, and chevron-patterned features. The contrast between coronae and the surrounding heavily cratered terrain is stark.
Notably, coronae are relatively crater-scarce, which suggests they are geologically younger than the older, cratered plains. Their internal ridges, grooves, and faults imply extensional forces, upward movement, or diapiric upwelling (i.e. material pushing upward from below).
Other Scars & Faults
Outside the coronae lie ancient, heavily cratered plains. But even these show fractures, grabens (down-dropped blocks), scarps, and terraces. Some boundaries look abrupt: sharply delineated transitions between smooth and rough terrains. The diversity is so striking that no two neighboring regions look alike.
Theories Behind the Patchwork
Why does Miranda look so chaotically assembled? Scientists have proposed several (non-exclusive) hypotheses:
1. Tidal Heating in Resonance
One leading idea is that in its past, Miranda was trapped in a 3:1 orbital resonance with Umbriel (another Uranian moon). This resonance would have forced Miranda into a more eccentric orbit, causing tidal flexing and internal frictional heating. That heating, even modest, might soften ice and allow flows or deformation.
As the ice heated and deformed, convection or diapirism might have pushed warm material upward, forming the coronae. The surface would stretch, crack, and rearrange.
2. Global Resurfacing by Convection
Geologic modeling suggests that convective overturning within the ice shell might explain resurfacing. In this scenario, warmer ice beneath could flow upward, disturb overlying layers, and rework the surface. Coronae might represent centers of upwelling, surrounded by faulted, stretched terrain.
3. Reassembly After Disruption
Some past models speculated that Miranda might have been partially shattered and later reassembled, producing a “patchwork” of crustal fragments. While intriguing, this idea is less favored now compared to internal deformation models.
4. Reorientation / True Polar Wander
The orientation of Miranda might have shifted over time. The creation of large, mass-redistributive structures (e.g. forming coronae) could alter its moment of inertia and cause reorientation. That would change how terrains appear relative to one another, possibly making the patchwork look more disjointed.
What’s New: Hidden Oceans and Recent Models
Recent studies have proposed that Miranda might once have hosted a subsurface ocean — at least partially — when its interior was warmer. In particular, new modeling suggests a scenario in which a liquid layer of 100 km thickness lay beneath an ice shell of ~30 km, active around 100–500 million years ago. That kind of interior state aligns with stress patterns matching the observed coronae and ridges.
If true, that implies more internal mobility in Miranda than previously believed, and it adds a new dimension to its “Frankenstein” appearance: a moon that might once have been active, but is now frozen in place.
Why Miranda Still Captivates
Miranda is small, dim, and remote. The only close images we have came from Voyager 2. Yet even with that limited data, it has become one of the most curious bodies in the outer Solar System. There’s no other moon in quite the same league in terms of topographic contrast.
Its oddities forced scientists to reconsider how small, icy bodies evolve. Miranda shows us that even modest tidal forces—and internal rearrangement—can leave lasting, dramatic scars.
As future missions to Uranus get proposed, Miranda is often flagged as a must-see target. A closer survey would shed light on the moon’s interior, confirm whether it once had an ocean, and help us connect the dots on how small worlds can display enormous geologic ambition.