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.

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

www.nasa.gov/hubble

or

hubblesite.org/news/2005/33

Eamonn A

Wonderful,thank you,this solar system has much more to offer us, I am sure!

Deirdre Kelleghan
IAS
www.irishastrosoc.org

Great Hubble links too Eamonn, cheers! I think I read somewhere that Uranus' rings are composed of one of the least reflective substances known in the solar system. Is this true?

I received yesterday technical/observational discovery details from Harvard Electronic Telegram no. 236. The information here is for those who are interested in alot more detail of the discovery.

RINGS OF URANUS

M. R. Showalter, SETI Institute; and J. J. Lissauer, Ames Research
Center, NASA, report the discovery of two rings of Uranus, R/2003 U 1 and
R/2003 U 2. Both are faint, dusty rings orbiting well beyond Uranus'
previously known ring system. R/2003 U 1 peaks in brightness at 97 700 km from the center of Uranus, coinciding with the orbit of Uranus XXVI (Mab), which is almost certainly the ring's primary source body. The ring has a broad triangular profile, with an inner limit at 86 000 km--near the orbit of Uranus XV (Puck)--and an outer limit at 103 000 km. R/2003 U 2 peaks in brightness at 67 300 km, where no known moons are present.

This ring also has a triangular profile, terminating near the orbits of Uranus XII (Portia) on the inside and Uranus XIII (Rosalind) on the outside. The rings are visible in data from the High Resolution Channel of the Hubble Space Telescope (HST) Advanced Camera for Surveys. They appear in 250-second clear-filter (300-700 nm) images obtained on 2003 Aug. 25 (24 images), 2004 Aug. 20 (40 images), 2004 Aug. 26 (40 images) and 2005 Aug. 20 (18 images). When images from a single date are co-added, S/N > 10. Both rings vary in brightness with the opening angle, as is expected for optically thin rings. R/2003 U 1 has a peak reflectivity at opposition (times the sine of the opening angle) of 9 x 10^(-7) and an estimated normal optical depth of 9 x 10^(-6). R/2003 U 2 has a peak of 4 x 10^(-7) and an estimated normal optical depth of 6 x 10^(-6)

I. de Pater, University of California at Berkeley; H. B. Hammel, Space
Science Institute; and S. Gibbard, Lawrence Livermore National Laboratory, write: "We report the detection of a faint uranian ring at a distance of about 67 700 km from Uranus (outside the epsilon ring). We identify this ring as the first ground-based detection of /2003 U 2, reported by Showalter and Lissauer above. We obtained the images at K' band (2.2 microns) on 2005 Aug. 23 UT with the 10-m Keck II Telescope (+ NIRC2/AO) on Mauna Kea. The small ring opening angle (about8.4 deg) and small phase angle (0.4 deg, close to opposition), along with a full hour of integration time, combined to make this faint ring detectable. We also made a probable detection of this same ring in Oct. 2005, but the ring opening and phase angles were less favorable. We searched out to 115 000 km from Uranus in Oct. 2005 and saw no additional rings. This will establish upper limits on the 2-micron brightness of any material out to that distance, including R/2003 U 1 reported by Showalter and Lissauer from HST data."

Eamonn A

Fascinating read. Begs to wonder how much more can be discovered in our backyard, so to speak...