The Major Moons Of Uranus Are Not That Different From Pluto

Voyager 2 images of the five largest Uranian moons Miranda, Ariel, Umbriel, Titania, and Oberon, with the diameter of each satellite shown to scale. NASA/JPL/MPIA

Uranus has only been visited by human probes once, and while we long to go back, there is still much we can do in exploring from afar. This latest discovery about the ice giant's moons started accidentally but has revealed some previously unknown facts about its five largest satellites.

As reported in the journal Astronomy & Astrophysics, researchers used data from the European Herschel Space Telescope to study Uranus's moons Titania, Oberon, Umbriel, Ariel, and Miranda. They were able to measure how the moons get heated by the light of the Sun, which is roughly 3 billion kilometers (1.87 billion miles) away.

The researchers discovered that these major moons store surface heat surprisingly well and cool down comparatively slowly. This profile is akin to what researchers have observed beyond the orbit of the other ice giant in our Solar System, Neptune, in dwarf planets like Pluto and Haumea.

These observations are in contrast with previous independent studies of the outer and irregular moons of Uranus. Those are similar to the Transneptunian Objects, smaller bodies that orbit the further edges of the Solar System. This duality of thermal properties is more evidence that the irregular moons might not have formed with the planet.

“This would fit with the speculations about the origin of the irregular moons,” co-author Thomas Müller, from the Max Planck Institute for Extraterrestrial Physics, said in a statement. “Because of their chaotic orbits, it is assumed that they were captured by the Uranian system only at a later date.”

The study used data from the now-defunct European Space Agency’s Herschel Observatory, an infrared space telescope. But getting the data wasn’t easy. The thermal signature of Uranus is extremely bright. These five moons are between 500 and 7,400 times fainter than the planet so the team had to come up with creative solutions to extract the faint signal from the moons. By knowing exactly where the moons were located, the team was able to pick up all of their signals around the planet.

“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,” lead author Örs Detre, from the Max Planck Institute for Astronomy, said.

The only spacecraft to visit Uranus was Voyager 2 in 1986. Performing just a quick flyby, the probe was limited to how much it could observe of the planet and its moons. Studies such as these provide important new insights that will have to tide us over until a new mission is sent to visit and explore.

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