The rings of Uranus are invisible to all except the largest telescopes ̵
The thermal glow gives the astronomers another window on the rings, which were only seen because they reflect some light in the visible or optical range and in the near infrared. With the new images of the Atacama Large Millimeter / Submillimeter Array (ALMA) and the Very Large Telescope (VLT), the team was first able to measure the temperature of the rings: cool 77 Kelvin or 77 degrees above absolute zero – – The boiling point of liquid nitrogen equals 320 degrees below zero Fahrenheit.
The observations also confirm that the brightest and densest ring of Uranus, called the Epsilon Ring, differs from the other known ring systems in our solar system, especially the spectacularly beautiful Saturn rings.
"Saturn's mostly icy rings are wide, bright, and have a range of particle sizes, from microns large dust in the innermost D-ring to several tens of meters in the main rings," he told Imke de Pater, a professor of astronomy at the University of California in Berkeley. "The small end is missing in the main rings of Uranus, the brightest ring, epsilon, consists of golf ball sized and larger stones."
In comparison, Jupiter's rings usually contain small particles in micrometer size (microns) thousandths of a millimeter). Neptune's rings are mostly dust, and even Uranus has broad layers of dust between its narrow main rings.
"We already know that the epsilon ring is a bit strange because we do not see the smaller stuff," said graduate student Edward Molter. "Something has swept out the smaller material, or it all fits together, we just do not know it, this is a step to understanding their composition and determining whether all rings are from the same source material or different for each ring."  Rings could be former asteroids caught in the planet's gravity, remnants of moons collapsing and shattering, remnants of moons that were torn apart when they came too close to Uranus, or debris from the time of formation 4.5 billion years ago.
The new data were published this week in the Astronomical Journal . De Pater and Molter conducted the ALMA observations, while Michael Roman and Leigh Fletcher of the University of Leicester in the United Kingdom conducted the VLT observations optically and infrared the albedo is much lower: they are really dark like charcoal, "said Molter are also extremely narrow in comparison to the rings of Saturn. The widest, the epsilon ring, is between 20 and 100 kilometers wide, while the Saturn is 100 or tens of thousands of miles wide. "
The lack of dust is large particles in Uranus' main rings were first discovered when the Voyager 2 flew around the planet and photographed it in 1986. However, the spaceship was unable to measure the temperature of the rings.
So far, astronomers have counted a total of 13 rings around the planet, with dust streaks between them in other respects from those of Saturn.
"It's cool that we can even do this with our instruments," he said, "I was just trying to make the planet look as good as possible, and I have the rings seen. It was amazing. "
Both VLT and ALMA observations were designed to study the temperature structure of the Uranus atmosphere, with VLT testing shorter wavelengths than ALMA.
" We were amazed to see how the rings clearly sprang out "This is an exciting opportunity for the upcoming James Webb Space Telescope, which will provide a tremendous amount of enhanced spectroscopic constraints on uranium rings in the coming decade.
Berkeley research funded by the National Aeronautics and Space Administration (NNX16AK14G) The work of Leicester University was supported by the European Research Council (GIANTCLIMES) under the Horizon 2020 research and innovation program of the European Union (723890) ,
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