Uranus’ moons have always been difficult to spot, as not only are they very small but they are covered in a very dark material. Oberon and Titania, Uranus’ biggest moons, were first spotted by the British astronomer William Herschel in 1787. In 1986, ten other moons were discovered. Among these moons are Desdemone and Cressida which could soon collide according to recent calculations.
Discovered in 1996 by the Voyager 2 probe, Cressida is a natural satellite of Uranus. We know very little about Cressida apart from it’s orbiting characteristics and estimations regarding it’s size. We do know that it belongs to the most densely packed group of satellites in the Solar System. Uranus’ nine moons have orbits which lie within 18,000 kilometres from one another. However the astrophysicist Robert Chancia from the University of Idaho has recently discovered the weight of Cressida. With this information, Chancia has also been able to determine the moon’s decline. He believes the moon will soon collide with another of the giant frozen planets’ satellites.
By studying Cressida’s orbiting rings, Chancia and his team have discovered that it’s orbit is slightly triangular rather than a perfect circle. Researchers believe that this small moon, which is only 82 kilometres in diameter, has a distorted orbit due to gravitational pulls. Individual particles in the ring orbit faster than the moon itself. These particles complete three orbits of Uranus while Cressida has completed only two. As a result, the team of researchers were able to determine the weight of the moon.
Cressida is supposedly quite light, weighing only about 1/300000th of Earth’s moon. According to researchers their discovery marks, “the first direct measurement of the weight of an internal satellite of Uranus.” Now that they know the moon’s mass and orbit, the researchers were then able to “predict” it’s future decline. Researchers believe that Cressida could collide with another of Uranus’ moons called Desdemone which is located only 900 km from Cressida’s orbit. Previous astronomers estimated this collision wouldn’t happen for another hundred million years. However this recent study predicts this event could happen within the next million years.