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Planetary News: Cassini-Huygens (2007)Four New Moons for SaturnBy Emily LakdawallaJuly 19, 2007 Both space-based and ground-based astronomers continue to find tiny bodies in orbit around the ringed planet. Ground-based observers Scott Sheppard, David Jewitt, Jan Kleyna, and Brian Marsden added three more irregular satellites, provisionally named S/2007 S1, S/2007 S2, and S/2007 S3, and the Cassini imaging team spotted a truly tiny one between Methone and Pallene, temporarily called S/2007 S4 (but apparently known inside the Cassini science team as "Frank"). In addition, four moons discovered in 2006 by Sheppard's team have lately received upgrades from their provisional designations to full names: Skoll (formerly known as S/2006 S8), Kari (S/2006 S2), Surtur (S/2006 S7), and Loge (S/2006 S5). Saturn can now boast 60 satellites. The Cassini discovery was made in images captured by the spacecraft on May 30, 2007. Among the many activities that the Cassini imaging team has instructed their camera to do is periodically to point at the edge of Saturn's rings and capture long time-series of images for the express purpose of searching for previously unobserved satellites. The team member whose job it is to sift through all these images, ignoring known moons and screening out image specks caused by cosmic ray hits on the camera's detector to search for undiscovered bodies, is Carl Murray of Queen Mary, University of London. "I was looking at images of the region near the Saturnian moons Methone and Pallene and something caught my eye," Murray says.
Saturn's total of 60 moons is approaching Jupiter's total of 63. However, unlike Saturn, Jupiter has not yet had the benefit of an orbital spacecraft that was able to perform these lengthy sets of observations to search for new moons. Galileo was in a position to do so, but alas, the failure of its high-gain antenna meant that it was not capable of broadcasting back to Earth the large numbers of images necessary for moon searches. The discovery of moons like S/2007 S4 at Jupiter will have to wait for another orbital mission. The names that Saturn's satellites receive depend upon where and how they orbit Saturn. Inner, regular satellites -- which most likely formed at the same time that Saturn did -- receive names associated with Titans or giants. However, most of Saturn's moons are irregular ones, occupying distant, elliptical, inclined or even retrograde orbits, which suggest that they are captured bodies. There are several distinct families of these satellites; within a family, satellites have similarly sized and inclined orbits. Prograde satellites belong to one of two families, which receive names from either Inuit or Celtic mythology. (Newly discovered or named satellites are in bold text.) Moons with prograde orbits and inclinations of about 34 degrees receive
Greek names: Moons with prograde orbits and inclinations around 45 degrees receive
Inuit names: All retrograde satellites -- of which there are many subfamilies -- receive names from Norse mythology. Moons with retrograde orbits and inclinations of 145 degrees: Moons with retrograde orbits and inclinations of 150 to 161 degrees: Moons with retrograde orbits and inclinations of 163 to 177 degrees: In addition to the four moons discovered this year, eight moons discovered in 2004 and 2006 still have yet to receive official names. |
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