Uranus rings the changes

This image from NASA's Hubble Space Telescope shows how the ring system around the distant planet Uranus appears at ever more oblique (shallower) tilts as viewed from Earth - culminating in the rings being seen edge-on in three observing opportunities in 2007 (Image © NASA)

New images of the planet Uranus have given Earth-based astronomers the first edge-on view of its rings since they were discovered in 1977.

Uranus only appears at this angle to the Earth every 42 years as the planet follows a leisurely 84-year orbit around the sun. The last time the rings were tilted edge-on to Earth, astronomers didn’t even know they existed.

The rings, made from fine dust particles, have changed significantly since the spacecraft Voyager photographed the planet 21 years ago. The inner rings are far more prominent than expected, revealing material in regions which were thought to be empty.

The fainter outer rings appeared in 2003 Hubble images, but were not noticed there until they were seen in 2005 Hubble images, which prompted astronomers to analyse the previous ones more carefully. Uranus has a total of 13 dusty rings.

Dr Imke de Pater, from the University of California at Berkeley, said: "There are a lot of forces acting on small dust grains, so it is not that crazy to find that the arrangement of rings has changed."

Uranus is the 7th planet from the sun. Its diameter, without the rings, is about 32,000 miles (51,000 kilometres) at the equator.

In the image, the edge-on rings appear as spikes above and below the planet. The rings cannot be seen running fully across the face of the planet because the bright glare of Uranus has been blocked out in the Hubble photo. A small amount of residual glare appears as a fan-shaped image artifact, along with an edge between the exposure for the inner and outer rings.

A number of different telescopes on Earth, as well as the orbiting Hubble space telescope, were used to observe the Uranus ring system.

Two small moons called Cordelia and Ophelia straddle the brightest "epsilon" ring and keep it in place. Astronomers believe analysis of the new images may reveal more moons.

The research was reported in the journal Science. 

 

This series of images from NASA's Hubble Space Telescope shows how the ring system around the distant planet Uranus appears at ever more oblique (shallower) tilts as viewed from Earth - culminating in the rings being seen edge-on in three observing opportunities in 2007. The best of these events appears in the far right image taken with Hubble's Wide Field Planetary Camera 2 on August 14, 2007 (Image © NASA, ESA, and M. Showalter/SETI Institute)
This series of images from NASA's Hubble Space Telescope shows how the ring system around the distant planet Uranus appears at ever more oblique tilts as viewed from Earth - culminating in the rings being seen edge-on in three observing opportunities in 2007. The best of these events appears in the far right image taken with Hubble's Wide Field Planetary Camera 2 on August 14, 2007.