Nevada and Miranda: Geologic Siblings a Billion Miles Apart
With 3 Mars missions, each representing a different country of origin, all reaching the red planet between February 9th and 19th this year, there is renewed global interest in what the surfaces of other worlds look like. Analog sites, places on Earth specifically studied due to their resemblance to conditions on another planet or moon, cover a variety of locales from the rugged desert of Utah as a stand-in for Mars to hydrothermal vents that might resemble hypothetical environments on the ocean moons Europa and Enceladus. While Nevada seems like a good analog for the cold deserts of Mars, there’s a much more interesting comparison that can be made between the Nevadan landscape and one of our solar system’s least studied worlds.
Uranus’ moon Miranda in approximate color (NASA/JPL/Jason Major)
Miranda: a celestial body 1/7th the size of our Moon that orbits the distant planet of Uranus. At over 1.5 billion miles (2.41 billion kilometers) from Earth, the only spacecraft to have seen the surface of this elusive moon was NASA's Voyager 2 in 1986. What little of Miranda they were able to image was, and still is, amazing. This far-flung world has one of the most unique landscapes in our entire solar system, including geologic features that haven’t been found anywhere else. Yet, the process believed to be behind Miranda’s one of a kind landscape is the exact same geologic process that defines Nevada’s terrain.
Nevada and sections of neighboring states from space (NASA/GSFC/MODIS)
Nevada has the most mountain ranges of any state at a whopping 314 named ranges. You may notice there are also countless "valleys" or basins, especially in the northern part of the state. The alternating pattern of basins and ranges cause Nevada's terrain to have a distinct wrinkly appearance from space. These peaks and valleys are known in geology as horst and graben. "Blocks" of the earth's crust move along faults, and if a set of blocks move so that one gets pushed up while the other drops down, they cause high ridges (the horsts) with ever-widening troughs (the grabens) between them. Thanks to this process, known as normal faulting or extensional faulting, the Great Basin desert is full of horst and graben.
Elsinore Corona (center) and a small part of Inverness Corona (bottom right) on the surface of Miranda (NASA/JPL/Jason Major)
Back on Miranda, the irregularly shaped regions of striping on its surface are called coronae. Three coronae are visible from the Voyager 2 images while computer modeling suggests there’s at least one additional corona on an unseen part of the moon. While the coronae themselves haven’t been found anywhere else in the solar system, part of their unique wrinkly striping is due to horst and graben. Of the three coronae, which are named Inverness, Elsinore, and Arden after places in Shakespeare plays, Elsinore Corona is the one where this geologic process is most noticeable. Well defined highs and lows in alternating bands make up the visible part of the Corona from Voyager 2’s images. These features create an even starker contrast on Miranda where the gravity is 1/124th as strong as it is on Earth, so geologic features are able to form to more extreme heights. Miranda also doesn’t have an atmosphere so there’s no erosion to wear down these dramatic landscapes, unlike here in Nevada where snowmelt, ice, rain, wind, and plants are all constantly at work breaking down the rock and flattening the terrain.
Left Photo: Verona Rupes (NASA/JPL-Caltech/Kevin M. Gill/Jason Major), Right Photos: Genoa Fault Scarp (Gigapan)
Both the lower gravity and lack of erosion also contribute to another incredible feature on Miranda’s surface. Near Inverness Corona is the fault scarp Verona Rupes, which is the tallest cliff in our solar system at 12 miles (20km) tall. The surface where two blocks of the crust meet to form a fault is called the faulting plane, and fault scarps are sections of this faulting plane that jut out of the ground after being pushed up by earthquakes along that fault. Verona Rupes is a fault scarp caused by normal faulting just like the horst and graben are. Similarly, Nevada also has visible fault scarps. One of the most striking is Genoa Fault Scarp, which is over 50 feet (15m) tall and found just south of Genoa, Nevada near Walley’s Hot Springs. It took multiple large earthquakes to raise this scarp, while the exact formation behind Verona Rupes is still unknown.
While these features may point towards Miranda being a geologically active world like Earth, it’s important to note that these features are likely very old even by geologic standards. Geologic activity is driven by heat within a celestial body. On Earth this heat is caused by the planet’s warm inner layers, fueled by churning material still hot from the Earth’s formation and heat put off by radioactive decay. On Miranda, the two leading ideas are that the heat needed for these processes was caused by the moon being pulled on by Uranus’ gravity and other moons, which might still be enough to keep geologic activity ongoing, or that the heat was generated from a one time massive impact with another object, which may never happen again.
While Miranda’s geologic past and future may remain unknown for decades, here in Nevada the horst and graben, fault activity, and widening of the Great Basin will continue for the foreseeable future. One day, maybe in our lifetimes, we’ll revisit this unique little moon of the Outer Solar System and be able to learn more things about it that remind us of home.
NASA page on Miranda: https://solarsystem.nasa.gov/moons/uranus-moons/miranda/in-depth/
NPS “Basin and Range Province”: https://www.nps.gov/articles/basinrange.htm?utm_source=article&utm_medium=website&utm_campaign=experience_more&utm_content=small
NPS “Horst and Graben”: https://www.nps.gov/articles/horst-and-graben.htm
UNR “Prominent Fault Scarps in Western Nevada”: