Miranda (moon)

Miranda is the smallest and innermost of the five round moons that orbit the planet Uranus. It was discovered by astronomer Gerard Kuiper on February 16, 1948, at McDonald Observatory in Texas. The moon is named after the character Miranda from William Shakespeare's play The Tempest. Like the other large moons of Uranus, Miranda orbits close to Uranus's equatorial plane. Because Uranus spins on its side as it travels around the Sun, Miranda's orbit is nearly perpendicular to the ecliptic—the plane of Earth's orbit around the Sun.

Miranda is very small, with a diameter of just 470 kilometers, or about 290 miles. Its surface area is roughly the same size as the U.S. state of Texas. The only close-up images we have of Miranda come from the Voyager 2 probe, which flew by Uranus in January 1986. During that flyby, Miranda’s southern hemisphere faced the Sun, so that is the part we studied.

Miranda has some of the most interesting and varied landscapes of any object in the Solar System. It features steep cliffs, such as Verona Rupes, which may be the tallest cliff known, rising about 20 kilometers high. The moon also has unusual chevron-shaped features called coronae, created by tectonic forces. Scientists are still working to understand how Miranda formed and why it looks the way it does.

Discovery and name

Miranda was discovered on 16 February 1948 by planetary astronomer Gerard Kuiper using the McDonald Observatory's 82-inch telescope. Its orbit around Uranus was confirmed a few weeks later. It was the first moon of Uranus found in nearly 100 years. Kuiper named it "Miranda" after a character in Shakespeare's The Tempest. The other moons of Uranus were also named after characters from Shakespeare or Alexander Pope.

Orbit

Miranda is the closest of Uranus's five round satellites, orbiting at about 129,000 km from the planet's surface. It is the smallest moon to orbit a major planet this closely. Miranda's orbital period is 34 hours, matching its rotation period, so it always shows the same face to Uranus, a condition called tidal locking.

Miranda's orbital inclination is unusually high at 4.34°, much greater than the other major moons of Uranus. Scientists aren't sure why this is, but they think it may have been influenced by past gravitational interactions with other moons. Unlike moons of Jupiter or Saturn, moons in the Uranian system can more easily escape these gravitational effects due to the planet's shape and the size of its satellites.

Observation and exploration

Miranda's apparent magnitude is +16.6, making it invisible to many amateur telescopes. Almost everything we know about its surface was learned when the spacecraft Voyager 2 flew by Uranus on January 24, 1986. This was the closest any spacecraft has come to Miranda, at a distance of 29,000 kilometers. The pictures surprised scientists, as Miranda's surface looked very different from what they expected. In 2017, NASA considered sending a new spacecraft to Uranus in the 2020s, choosing it over Neptune because the travel time would be shorter.

Composition and internal structure

Miranda is the least dense of Uranus's round satellites, with a density that suggests it is made up of more than 60% water ice. Its surface appears to be mostly water ice, but it contains more rock compared to similar moons of Saturn. This indicates that heat from radioactive decay might have caused rocks and organic compounds to settle inside Miranda.

Miranda is not perfectly round, being slightly wider around the equator than at the poles. Scientists think Miranda may have had a liquid ocean about 100 km thick beneath its surface in the past few hundred million years. One theory is that Miranda's past orbit around Uranus caused tidal heating, which could have warmed its interior enough to create this ocean.

Geography

Miranda has a very interesting surface with many different features like fractures, valleys, craters, ridges, and cliffs. Some areas are older and darker with many craters, while other parts have bright and dark strips and complex patterns of ridges. Scientists believe Miranda's surface is made mostly of water ice, with some silicate rocks and other materials buried beneath.

Miranda is special because it has large circular features called coronae. There are three known coronae: Inverness Corona near the south pole, Arden Corona, and Elsinore Corona. These areas have unique patterns and structures, including bright and dark bands, and they show evidence of past geological activity. Miranda also has huge cliffs called rupes, with some faults being very old and others more recent. During the Voyager 2 mission in 1986, scientists observed many craters on Miranda, mostly in the southern hemisphere. These craters vary in shape and size, and their numbers help scientists understand the age of different surface areas on Miranda.

Origin and formation

Miranda, a moon of Uranus, has several theories about how it formed and changed over time. One idea is that it formed from a disk of gas and dust around Uranus, either naturally or after a big collision. Miranda has some very young surface areas, which is surprising because such small moons usually cool quickly and stop changing.

Scientists think Miranda's surface changed a lot due to things like tidal forces from Uranus, possible collisions with other space objects, and movements inside the moon. These forces might have stretched and twisted Miranda's materials, creating cracks and patterns we see today. Over billions of years, Miranda went through many stages of heating and cooling, which helped shape its surface into the mix of old craters and younger areas we see now.