• Sai Charan

Miranda: The Moon Of Uranus

Miranda as seen from Voyager-2. Credit: NASA/JPL-Caltech.

The smallest satellite of Uranus is Miranda. It also has the closest orbit to Uranus. It was discovered by Gerald Kuiper on 16 February 1948 at McDonald Observatory, Texas. It is named after Miranda from William Shakespeare’s play The Tempest. The crater count of Miranda indicates that it is old with a similar geological history to that of its fellow satellites. Few of the craters are very huge suggesting that most of the craters have formed in its distant past. It has a diameter of just 470 km and has less than 1% of the gravity on Earth.

Miranda likely has an inner core of rock and a mantle of ice. The temperature at its south pole is about 85 Kelvin. Pure water ice adopts the characteristics of rocks at this temperature. Astrophysicists have observed that the substance behind the surfacing of Miranda is too viscous to be just pure water but too fluid to be solid water. Therefore, It is thought to be consisting of a mixture similar to that of lava, and composed of water and ammonia, and likely freezes at 176 Kelvin. This indicates that Miranda might not have a uniform composition and temperature.

Uranus appears approximately forty times larger from Miranda when compared to the Moon from the Earth. Although it is very small, about one-seventh the size of our moon, it is home to the highest cliff in the solar system, the Verona Rupes. It is widely known for its chevron-shaped tectonics called Coronae. The most popular theory that was able to explain the formation of the coronae in the 20th century was that Miranda could have been smashed apart by a massive impact and reassembled in a haphazard way creating the Coronae. However, recent strides in research solutions have suggested that the Coronae have formed due to the upwelling of warm ice from Miranda itself.

It has a broken terrain and has canyons hundreds of kilometers long and tens of kilometers wide. Voyager 2 visited this natural satellite in February 1986. It could take photos of only the Southern Hemisphere of Miranda due to Uranus’s orientation. The central mystery is the weird topography of it. A celestial body that is as small as it would most likely not have enough internal energy to produce the geographical structures seen on it.

The most widely accepted hypothesis today is that the structures could have been created due to tidal heating when it was in an orbital resonance with its fellow satellite Umbriel. The resonance might have increased its orbital eccentricity to 0.1 and could have generated tidal friction. The force of the tidal friction could have increased as it moved towards Uranus and decreased as it moved away from Uranus. These changes in the net force exerted on Miranda might have warmed it and caused melting.

I believe that sending another space probe to the Northern Hemisphere of Miranda can help us ascertain the facts. The Northern Hemisphere of Miranda might just be waiting to unravel itself.