Four decades after their detection,
the 13 enigmatic rings around Uranus stunned astrophysicists again this summer.
In June, new pictures captured their warm glow for the first time. Well, warm
for Uranus.
At -320 degrees Fahrenheit,
the rings are 10 degrees warmer than the
planet's surface, which is the coolest in our solar system. Researchers found
the rings' temperature thanks to these thermal imageries. The results were
described in a study issued
last month in The Astronomical Journal. To take the images, scientists used
the Atacama Large Millimeter Array and the Very Large Telescope in Chile to
measure the temperature structure of Uranus' atmosphere. They were astonished
to discover that they'd picked up thermal readings of the planet's rings.
"It's cool that we can
even do this with the instruments we have," Edward Molter, a graduate
student at the University of California at Berkeley and the study's lead
author, said
in a press release. "I was just trying to image the planet as best I
could and I saw the rings. It was amazing."
Molter and his coauthor Imke
de Pater, a professor of astronomy, made the above composite image, which displays
the rings' thermal glow at radio wavelengths. The dark bands in the picture
capture molecules that absorb radio waves; in Uranus' case, that's possibly hydrogen
sulfide. The yellow spot is the planet's North Pole, where those molecules
are thin.
"We were astonished to
see the rings jump out clearly when we reduced the data for the first
time," said Leigh Fletcher, who led the telescope observations.
The study established that
Uranus' epsilon ring — the brightest, broadest, and thickest of the planet's
rings — is peculiar among other rings in our solar system. Saturn's ice rings,
bright and wide enough to see with a typical telescope, are made of particles
of variable sizes, from dust with a width of one-thousandth of a millimeter to
house-sized chunks of ice. Jupiter's and Neptune's rings are generally made up
of those tiny dust particles. Uranus' epsilon ring, though, comprises only of rocks
at least the size of golf balls.
"We already know that
the epsilon ring is a bit weird, because we don't see the smaller stuff,"
Molter said. "Something has been sweeping the smaller stuff out, or it's
all glomming together. We just don't know. This is a step toward understanding
their composition and whether all of the rings came from the same source
material, or are different for each ring."
Astrophysicists first discovered
Uranus' rings in 1977. It took so long to detect them since they're much
thinner and darker than Saturn's rings. They reflect only minute amounts of
light in the visible range, with more reflection in the infrared and
near-infrared ranges.
"They are really dark,
like charcoal," Molter said.
After Voyager 2 soared by
Uranus and captured the first up-close pictures of the planet in 1986, researchers
observed the lack of tiny dust particles in its rings. The reasons for this distinctive
ring makeup are still unknown. Uranus' rings could have come from asteroids
that fell into orbit around Uranus, the leftovers of moons that collided with
each other or got torn apart by the planet's gravity, or discarded debris from
the creation of the solar system.
NASA's James Webb Space
Telescope, set to launch in 2021, should be capable of observing the enigmatic
rings in greater detail.
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