Saturn is not the only object in the Solar System with rings. The other gas giants, as well as a few asteroids, have rings too, although they're certainly not quite as ostentatious. Uranus has rings that are very difficult to see as they reflect very little light. For this reason, researchers recently used a different approach to study them and were able to measure their temperature for the first time.
In a paper accepted for publication in The Astronomical Journal, researchers discuss observations conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Very Large Telescope (VLT) to estimate that the main rings are at a chilling -196.15°C (-321.07°F ), roughly the boiling point of nitrogen.
The study shows how different these rings are from any others in the Solar System. In particular, the epsilon ring, the densest and brightest in the Uranian system, is unlike any other we have studied so far.
“The rings of Uranus are compositionally different from Saturn’s main ring, in the sense that in optical and infrared, the albedo is much lower: they are really dark, like charcoal,” lead author Edward Molter, from the University of California, Berkeley, said in a statement. “They are also extremely narrow compared to the rings of Saturn. The widest, the epsilon ring, varies from 20 to 100 kilometers [12-62 miles] wide, whereas Saturn’s are hundreds or tens of thousands of kilometers wide.”
But it is also the size of the particles that make up the rings. Uranus' particles don't show the same variation as the particles present in Saturn’s rings. Most of the smaller particles have either been swept away or are clumped up in the structures seen in the observations.
“Saturn’s mainly icy rings are broad, bright and have a range of particle sizes, from micron-sized dust in the innermost D ring, to tens of meters in size in the main rings,” said Imke de Pater, a UC Berkeley professor of astronomy. “The small end is missing in the main rings of Uranus; the brightest ring, epsilon, is composed of golf ball-sized and larger rocks.”
While several mysteries endure, these observations will help researchers to model possible origin scenarios for the rings. Currently, we don’t know if they are the remains of an asteroid captured by the planet, remnants of moons that crashed into each other or were destroyed by Uranus, or even just debris from the very beginning of the Solar System.