The rings of Uranus are invisible to all but the largest telescopes-they were not even discovered until 1977-but they're surprisingly bright in new heat images taken by two large telescopes in the high deserts of Chile.
The thermal glow gives astronomers another window on the rings, which they reflect because they are a little light in the visible, or optical, range and in the near-infrared. The new images taken by the Atacama Large Millimeter / submillimeter Array (ALMA) and the Very Large Telescope (VLT) allowed 77 Kelvin, or 77 degrees above absolute zero
The observations also confirm that Uranus's brightest and densest ring, called the epsilon ring, differs from the other known ring systems in our solar system, in particular the spectacularly beautiful rings of Saturn.
"Saturn's mainly icy rings are broad, bright and have a range of particle sizes, from micron-sized dust to the inside diameter," said Imke de Pater, a UC Berkeley professor of astronomy.
By comparison, Jupiter's rings are mostly small, micron-sized particles (a micron is a thousandth of a millimeter).
"We already know that the epsilon ring is a bit weird because we do not see the smaller stuff," said Graduate student Edward Molter. "Something has been sweeping the smaller stuff out, or it's all glomming together." We just do not know . "
Rings could be former asteroids captured by the planet's gravity, remnants of moons that crashed into one another and shattered, the remains of moons torn apart when they got too close to Uranus, or remains 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 led the ALMA observations, while Michael Roman and Leigh Fletcher from the University of Leicester in the United Kingdom led the VLT observations.
"The rings of Uranus are 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, "Molter said. Saturn's are 100's or thousands of kilometers wide. "
The lack of dust-sized particles in Uranus's main rings what first noted when Voyager 2 flew by the planet in 1986 and photographed them. The spacecraft was unable to measure the temperature of the rings, however.
To date, astronomers have counted a total of 13 around the planet, with some bands of dust between the rings. The rings differ in other ways from those of Saturn.
"It's cool that we can not do this with the instruments," he said. It was amazing. "
Both the VLT and ALMA observations were designed to explore the temperature structure of Uranus' atmosphere, with VLT probing shorter wavelengths than ALMA.
"This is an exciting opportunity for the upcoming James Webb Space Telescope, which will be vastly improved spectroscopic constraints on the Uranian rings in the coming decade.
Thermal Emission from the Uranian Ring System, arXiv: 1905.12566 [astro-ph.EP] arxiv.org/abs/1905.12566
Astronomers see 'warm' glow of Uranus's rings (2019, June 20)
retrieved 20 June 2019
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