While observing Uranus, astronomers made an accidental discovery: According to infrared images of Uranus’ five main satellites, their composition is closer to that of dwarf planets such as Pluto and Haumea, that is, compact rock objects with an icy crust.
We don’t have many observations of Uranus, as the frozen giant orbits the Sun at an average distance of about 20 times that of Earth. Observe the celestial body with Earth’s telescopes, makes moons very difficult to see; they are much smaller and reflect much less sunlight than Uranus, so they are dimmed.
“The moons, which are between 500 and 7,400 times fainter on the planet, are so close to Uranus that they merge with equally bright celestial bodies.“, according to astronomer Gábor Marton of the Konkoly Observatory in Hungary.”Only the brightest moons, Titania and Oberon, stand out a little from the surrounding glow.“
The five main moons of Uranus are, in decreasing order of magnitude, Titania, Oberon, Umbriel, Ariel and Miranda. All five satellites have a rounded shape. This indicates the achievement of hydrostatic equilibrium, i.e. a mass sufficient to develop a symmetrical and rounded shape under its own gravity. And they also appear to be composed of rock and ice.
These five main moons are very similar to the dwarf planets Pluto and Haumea, with their dense rocky bodies and ice-encrusted surfaces. This suggests that Titania, Oberon, Umbriel, Ariel and Miranda have formed in the same way, although the exact chemical composition of the rock and ice is yet to be determined.
The discovery was made during observations by a team of astronomers between 2010 and 2012. When the team subtracted Uranus from the data using a specially developed algorithm, the discovery emerged. “We were all surprised when four moons clearly appeared on the images, and we could even detect Miranda, the smallest and innermost of the five largest Uranian moons.“said astronomer Örs H. Detre of the Max Planck Institute for Astronomy.