The solar system's tallest cliff would take 12 minutes to fall down
On Uranus's small moon Miranda sits Verona Rupes, an enormous cliff estimated to be around 20 kilometers deep—roughly ten times deeper than the Grand Canyon. Because Miranda has very weak gravity, an astronaut stepping off the top of this precipice would fall freely for over 12 minutes before reaching the bottom.
An Improbable Precipice in the Outer Solar System
Perched on the icy surface of Uranus's moon Miranda lies Verona Rupes, an enormous cliff face widely regarded as the tallest known scarp in the solar system. While estimates of its exact vertical drop vary among planetary scientists, the scarp is frequently cited as reaching depths of up to twenty kilometers. To put that scale into perspective, Verona Rupes plunges more than ten times deeper than the Grand Canyon in Arizona and surpasses the total height of Mount Everest above sea level more than twice over. On a planetary body with a diameter of only roughly 470 kilometers, a vertical feature of this magnitude is extraordinary, making Miranda one of the most topographically extreme worlds known.
The sheer proportions of Verona Rupes challenge intuitive notions of planetary geology. On Earth, massive vertical cliffs are constantly eroded and worn down by wind, water, and tectonic restructuring, while the planet's strong gravity limits how steep a rock wall can become before collapsing under its own weight. On Miranda, however, the freezing conditions of the outer solar system and the moon's predominantly water-ice crust have preserved an almost vertical face that cuts deep into the frozen crust, serving as a monument to ancient and violent geological forces.
The 1986 Encounter: Discovery by Voyager 2
Verona Rupes was revealed to humanity in January 1986, when NASA's Voyager 2 spacecraft executed its historic flyby of the Uranian system. Because Uranus and its moons are tilted dramatically on their sides relative to the plane of the solar system, Voyager 2 was only able to map the sunlit southern hemispheres of the Uranian satellites during its rapid pass. Among all the moons observed, Miranda was the closest target of the encounter, and the images sent back stunned planetary geologists who had expected a cold, geologically inactive ball of ice.
Instead, the photographs depicted a chaotic jigsaw of distinct geological terrains. Alongside smooth, heavily cratered regions were massive grooved structures and enormous fault lines, with Verona Rupes standing out prominently at the edge of one of these dramatic zones. In accordance with the International Astronomical Union's convention of naming Uranian moons after characters from the works of William Shakespeare and Alexander Pope, features on Miranda are named after locations and characters in Shakespeare's plays. Verona Rupes was named after the Italian city of Verona, the primary setting of Romeo and Juliet.
The Physics of a Twelve-Minute Fall
The headline-grabbing aspect of Verona Rupes is the surreal experience of falling from its edge. Miranda is a very small moon with a fraction of Earth's mass, resulting in a surface gravity of less than one percent of Earth's—approximately 0.08 meters per second squared. Combined with the total absence of a substantial atmosphere, any object dropped from the top of the cliff would experience pure, unhindered gravitational acceleration without any aerodynamic drag or terminal velocity limit imposed by air resistance.
Under these conditions, a dropped object or an intrepid astronaut stepping off the edge would accelerate at a languid pace compared to Earth. It would take roughly twelve minutes of continuous free fall to traverse the estimated twenty-kilometer drop. However, despite the slow rate of acceleration, the continuous accumulation of speed over such a vast distance means that the falling object would reach the bottom travelling at roughly 140 to 200 kilometers per hour (roughly 90 to 125 miles per hour). Without an active propulsion system or specialized landing mechanism, the impact at the base would remain catastrophic.
Theories of Formation: Tectonics and Disruption
How a diminutive moon like Miranda developed such monumental topography remains a central question in planetary science. Miranda's surface is scarred by giant, ovoid-to-trapezoidal structures known as coronae—specifically named Arden, Elsinore, and Inverness Coronae. Verona Rupes is closely associated with this complex terrain, appearing as a massive extensional fault, or graben wall, where the crust was pulled apart by immense internal stress.
Two main hypotheses have competed to explain this extreme geological activity. An early, dramatic theory proposed that Miranda was catastrophically shattered by a massive impact early in its history, after which the fragments gravitationally reassembled in a jumbled, haphazard arrangement with dense silicate rock and lighter water ice settling irregularly. A more widely accepted modern model suggests that Miranda experienced intense tidal heating caused by orbital resonances with other Uranian moons. This internal heating may have driven diapirism—the buoyant upwelling of warm, less-dense subsurface ice—which stretched and cracked the brittle surface crust, producing enormous normal faults and deep tectonic canyons like Verona Rupes.
Measurement Uncertainties and Geological Context
While the twenty-kilometer estimate is widely cited, determining the precise depth of Verona Rupes from Voyager 2's single flyby dataset involves notable uncertainties. Scientists rely on shadow measurements, limb profiles, and stereo imaging derived from the limited angles captured during the encounter. Consequently, alternate scientific estimates place the vertical scarp height anywhere between five and ten kilometers in certain sections, with the twenty-kilometer mark representing the upper bound or cumulative drop across the fault zone.
Even at the conservative estimate of five to ten kilometers, Verona Rupes remains exceptionally steep and stands among the most dramatic sheer vertical faces in the known solar system. For comparison, the vast canyon system of Valles Marineris on Mars features walls up to eight kilometers deep, but these slope at gentler angles across vast distances. Verona Rupes is distinguished by the sheer steepness of its exposed scarp wall relative to the tiny radius of the world it occupies.
What Verona Rupes Reveals About Ice Worlds
The existence of Verona Rupes fundamentally reshaped planetary scientists' understanding of small icy satellites. Prior to Voyager 2's encounter with Miranda, prevailing models suggested that small, distant moons would lack the heat energy required to drive extensive tectonic deformation, remaining largely static, heavily cratered relics. Miranda proved that even modest gravitational interactions and tidal forces can leave enduring scars on icy worlds.
Verona Rupes also serves as a prime candidate for future exploration. Because Voyager 2 only provided a brief snapshot of Miranda's southern hemisphere, more than half of the moon remains completely unmapped at high resolution. Proposed future missions to the Uranian system, such as a dedicated Uranus orbiter and probe, aim to capture comprehensive 3D topographical data of Miranda, allowing scientists to confirm the precise geometry of Verona Rupes and finally resolve the mysteries of its formation.
Key takeaways
•Verona Rupes on Uranus's moon Miranda is estimated to be up to 20 kilometers deep, making it the tallest known cliff face in the solar system.
•Because Miranda has less than one percent of Earth's gravity and no atmosphere, falling from the cliff would take over twelve minutes, reaching an impact speed of roughly 140 to 200 kilometers per hour.
•The scarp was discovered during the Voyager 2 flyby in 1986 and was named after the setting of William Shakespeare's Romeo and Juliet.
•Geologists believe Verona Rupes formed either through intense extensional faulting driven by tidal heating and upwelling ice, or via the catastrophic breakup and reassembly of the moon.