Uranus has got a big, icy ring (Getty Images/Stocktrek Images)

For the first time ever astronomers have been able to measure the temperatures of one of the rings around Uranus.

They found that the faint clusters of ice and rock that surround the blue giant are a frosty 77 kelvin. That’s about the same temperature as the boiling point of liquid nitrogen.

Or, to put it another way, nearly -200 degrees Celsius.

The researchers used thermal imaging from the Atacama Large Millimeter Array and Very Large Telescope, based in Chile, to probe the distant planet. The fact that Uranus has rings (13 of them) wasn’t even known until 1977 because they’re so faint/




The paper outlining the discovery is titled Thermal Emission From The Uranian Ring System and was published in the Astrophysics Journal.

Composite image of Uranus’s atmosphere and rings at radio wavelengths, taken with the ALMA array – they measure a frigid 77 kelvin (UC Berkeley image by Edward Molter and Imke de Pater)

‘Saturn’s main icy rings are broad, bright and have a range of particle sizes, from micron-sized dust in the innermost D ring, to tens of metres in size in the main rings,’ said Imke de Pater, coauthor of the paper and an astronomy professor at the University of California, Berkeley, in the US. ‘The small end is missing in the main rings of Uranus; the brightest ring, epsilon, is composed of golf ball-sized and larger rocks.’

Uranus widest ring is called Epsilon and stretches 100 kilometers wide. That’s a fraction of the size of Saturn’s, which stretch for tens of thousands of kilometers.

While the rings are composed of dust, ice and rock, astronomers still aren’t able to really dig in and see if there are different particles in there.

‘We already know that the epsilon ring is a bit weird, because we don’t 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 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.’

Uranus, pictured during Nasa’s Voyager 2 flyby (Nasa)

At present, the best we can do is say the rings are made up from chunks of material from asteroid or moon fragments left over from the formation of the solar system four and a half billion years ago.

There may even be more than 13 rings around Uranus. Scientists are continuing to study the planet to unlock its secrets and they plan to use the soon-to-be-launched James Webb Space Telescope to look at it in greater detail.