|
|
Rhea: Saturn's Second Larges
…
| Title |
Rhea: Saturn's Second Largest Moon |
| Explanation |
Rhea [ http://www.nineplanets.org/rhea.html ] is the second largest moon of Saturn [ http://pds.jpl.nasa.gov/planets/choices/saturn1.htm ], behind Titan [ http://www.nineplanets.org/titan.html ], and the largest without an atmosphere. It is composed mostly of water ice, but has a small rocky core. Rhea [ http://www.solarviews.com/eng/rhea.htm ]'s rotation and orbit are locked together (just like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ]) so that one side always faces Saturn. A consequence of this is that one side always leads the other. Rhea's leading surface is much more heavily cratered than its trailing surface. The above photograph [ http://www.solarviews.com/cap/sat/rhea2.htm ] was taken with the Voyager 1 spacecraft [ http://voyager.jpl.nasa.gov/spacecraft/index.html ] in 1980. NASA's Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/ ] is currently on route to Saturn and will arrive in 2004. |
|
Saturn, Rings, and Two Moons
| Title |
Saturn, Rings, and Two Moons |
| Explanation |
NASA's robot spacecraft Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap960629.html ] 2 made this image [ http://nssdc.gsfc.nasa.gov/photo_gallery/caption/saturn.txt ] of Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ] as it began to explore the Saturn system [ http://www.jpl.nasa.gov/cassini/Images/astro/23209.html ] in 1981. Saturn's famous rings [ http://ringside.arc.nasa.gov/www/saturn/saturn.html ] are visible along with two of its moons, Rhea [ http://bang.lanl.gov/solarsys/rhea.htm ] and Dione [ http://antwrp.gsfc.nasa.gov/apod/ap951009.html ] which appear as faint dots on the right and lower right part of the picture. Astronomers believe that Saturn's moons play a fundamental role in sculpting its elaborate ring system [ http://newproducts.jpl.nasa.gov/saturn/back.html ]. A robot spacecraft named Cassini [ http://www.jpl.nasa.gov/cassini/ ] was launched [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] last October and is expected to rendezvous [ http://www.jpl.nasa.gov/cassini/Mission/tour.html ] with the giant gas planet in 2004. |
|
Sylvia, Romulus and Remus
| Title |
Sylvia, Romulus and Remus |
| Explanation |
Discovered in 1866, main belt asteroid [ http://www.nineplanets.org/asteroids.html ] 87 Sylvia lies 3.5 AU from the Sun, between the orbits of Mars and Jupiter. Also shown in recent years to be one in a growing list of double asteroids [ http://antwrp.gsfc.nasa.gov/apod/ap001101.html ], new observations during August and October 2004 made at the Paranal [ http://antwrp.gsfc.nasa.gov/apod/ap050817.html ] Observatory convincingly demonstrate that 87 Sylvia in fact has two moonlets - the first known triple asteroid system [ http://www.eso.org/outreach/press-rel/pr-2005/ pr-21-05.html ]. At the center of this composite of the image data, potato-shaped 87 Sylvia itself is about 380 kilometers wide. The data show [ http://www.obspm.fr/actual/nouvelle/aug05/sylvia.en.shtml ] inner moon, Remus, orbiting Sylvia at a distance of about 710 kilometers once every 33 hours, while outer moon Romulus orbits at 1360 kilometers in 87.6 hours. Tiny Remus and Romulus are 7 and 18 kilometers across respectively. Because 87 Sylvia was named after Rhea Silvia [ http://www.pantheon.org/articles/r/rhea_silvia.html ], the mythical mother of the founders of Rome, the discoverers [ http://www.berkeley.edu/news/media/releases/2005/08/ 10_sylvia.shtml ] proposed Romulus and Remus as fitting names [ http://www.eso.org/outreach/press-rel/pr-2005/ pr-21-05_p2.html ] for the two moonlets. The triple system is thought to be the not uncommon result of collisions producing low density, rubble pile [ http://www.boulder.swri.edu/~bottke/rubble/rub.html ] asteroids that are loose aggregations of debris. |
|
|
