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 in 1948 at McDonald Observatory in Texas. The moon is named after a character 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, 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 about 470 kilometers, or 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.

Miranda has some of the most interesting landscapes of any object in the Solar System. It features steep cliffs, such as Verona Rupes, which may be one of the tallest cliffs known. The moon also has unusual shapes called coronae, created by tectonic forces. Scientists are still learning more about how Miranda formed and why it looks the way it does.

Discovery and name

Miranda was found on 16 February 1948 by astronomer Gerard Kuiper. He used a big telescope at the McDonald Observatory. Its path around the planet Uranus was checked a few weeks later. It was the first moon of Uranus found in almost 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. It orbits 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. This means it always shows the same face to Uranus, a condition called tidal locking.

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

Observation and exploration

Miranda's apparent magnitude is +16.6, which means it is too faint to see with many small telescopes. Most of what we know about Miranda comes from when the spacecraft Voyager 2 flew by Uranus on January 24, 1986. This was the closest any spacecraft has ever come to Miranda, at a distance of 29,000 kilometers. The pictures from Voyager 2 surprised scientists because Miranda's surface looked very different from what they expected. In 2017, NASA thought about sending a new spacecraft to Uranus in the 2020s because it would take less time to get there than to Neptune.

Composition and internal structure

Miranda is the least dense of Uranus's round satellites. Its density shows it is made of more than 60% water ice. Its surface looks mostly like water ice, but it has more rock than similar moons of Saturn. This suggests that heat from radioactive decay may have caused rocks and organic compounds to move inside Miranda.

Miranda is not a perfect circle. It is a little wider around the middle than at the poles. Scientists think Miranda may have had a liquid ocean about 100 km thick under its surface in the past few hundred million years. One idea is that Miranda's old path around Uranus caused tidal heating, which might have warmed its inside enough to make 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 is a moon of Uranus. Scientists have different ideas about how it formed and changed. One idea is that it formed from a disk of gas and dust around Uranus, maybe after a big collision.

Miranda's surface looks young in some places, which is surprising because small moons usually cool quickly. Scientists think Miranda's surface changed a lot because of 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, making cracks and patterns we see today. Over billions of years, Miranda went through many stages of heating and cooling, shaping its surface with old craters and younger areas.