[meteorite-list] NASA's Hubble Discovers New Rings and Moons Around Uranus

[Ron Baalke]

Dec. 22, 2005

Dwayne Brown/George Deutsch
Headquarters, Washington
(202) 358-1726/1324

Ray Villard
Space Telescope Science Institute, Baltimore
(410) 338-4514 

RELEASE: 05-590

NASA'S HUBBLE DISCOVERS NEW RINGS AND MOONS AROUND URANUS

NASA's Hubble Space Telescope photographed a new pair of rings around 
Uranus and two new, small moons orbiting the planet. 

The largest ring is twice the diameter of the planet's previously 
known rings. The rings are so far from the planet, they are being 
called Uranus' "second ring system." One of the new moons shares its 
orbit with one of the rings. Analysis of the Hubble data also reveals 
the orbits of Uranus' family of inner moons have changed 
significantly over the past decade. 

"The detection of these new interacting rings and moons will help us 
better understand how planetary systems are formed and sustained, 
which is of key importance to NASA's scientific exploration goals," 
said Dr. Jennifer Wiseman, program scientist for Hubble at NASA 
Headquarters. 

Since dust orbiting Uranus is expected to be depleted by spiraling 
away, the planet's rings must be continually replenished with fresh 
material. "The new discoveries demonstrate that Uranus has a youthful 
and dynamic system of rings and moons," said Mark Showalter of the 
SETI Institute, Baltimore. 

Showalter and Jack Lissauer of NASA's Ames Research Center, Moffet 
Field, Calif., propose that the outermost ring is replenished by a 
12-mile-wide newly discovered moon, named Mab, which they first 
observed using Hubble in 2003. 

Meteoroid impacts continually blast dust off the surface of Mab. The 
dust then spreads out into a ring around Uranus. Mab's ring receives 
a fresh infusion of dust from each impact. Nature keeps the ring 
supplied with new dust while older dust spirals away or bangs back 
into the moon. 

Showalter and Lissauer have measured numerous changes to the orbits of 
Uranus' inner moons since 1994. The moon's motions were derived from 
earlier Hubble and Voyager observations. "This appears to be a random 
or chaotic process, where there is a continual exchange of energy and 
angular momentum between the moons," Lissauer said. His calculations 
predict moons would begin to collide as often as every few million 
years, which is extraordinarily short compared to the 4.5 billion 
year age of the Uranian system. 

Showalter and Lissauer believe the discovery of the second ring, which 
orbits closer to the planet than the outer ring, provides further 
evidence that collisions affect the evolution of the system. This 
second ring has no visible body to re-supply it with dust. The ring 
may be a telltale sign of an unseen belt of bodies a few feet to a 
few miles in size. Showalter proposes that a previous impact to one 
of Uranus' moons could have produced the observed debris ring. 

Hubble uncovered the rings in August 2004 during a series of 80, 
four-minute exposures of Uranus. The team later recognized the faint 
new rings in 24 similar images taken a year earlier. Images from 
September 2005 reveal the rings even more clearly.

Showalter also found the rings in archival images taken during Voyager 
2's flyby of Uranus in 1986. Uranus's first nine rings were 
discovered in 1977 during observations of the planet's atmosphere. 
During the Voyager encounters, two other inner rings and 10 moons 
were discovered. However, no one noticed the outer rings, because 
they are extremely faint and much farther from the planet than 
expected. Showalter was able to find them by a careful analysis of 
nearly 100 Voyager images.

Because the new rings are nearly transparent, they will be easier to 
see when they tilt edge-on. The new rings will increase in brightness 
every year as Uranus approaches its equinox, when the sun shines 
directly over the planet's equator. When it happens in 2007, all of 
the rings will be tilted edge-on toward Earth and easier to study. 
These research data will appear in an upcoming issue of the journal 
Science.

The Hubble Space Telescope is a project of international cooperation 
between NASA and the European Space Agency. The Space Telescope 
Science Institute in Baltimore conducts Hubble science operations. 
The Institute is operated for NASA by the Association of Universities 
for Research in Astronomy, Inc., Washington. The Harvard-Smithsonian 
Center for Astrophysics in Cambridge, Mass. is a joint collaboration 
between the Smithsonian Astrophysical Observatory and the Harvard 
College Observatory. 

For images and information about Hubble and this research on the Web, 
visit: 

http://www.nasa.gov/hubble 

or 

http://hubblesite.org/news/2005/33 

	
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