7/20/2023 0 Comments Sarurn moon atlas pancake![]() ![]() How did Pan get its strange shape? The leading idea is that the flange of ice around its equatorial bulge is ring material swept up and collected by the moon as it cruises through the Encke Gap. Brave Little Moonįor a while now, scientists have had a hunch that there's something askew about Pan and Atlas, based on distant views obtained by Cassini in 2007. While the Daphnis is slightly inclined to the plane of Saturn's rings by 0.0036 degrees and kicks up vertical waves in its wake, the orbit of Pan is nearly flat with an inclination of only 0.0001 degrees, and it induces spiral density waves in the ring plane. Unlike the narrow 35-kilometer-wide Keeler gap occupied by the tiny moonlet Daphnis, the wider 325-kilometer Encke Gap also hosts a tenuous ringlet that Pan braids and modifies. The moon has an albedo (or reflectance) of 50%, equivalent to dirty snow. On Earth, Pan would just barely fit inside Tampa Bay. The moon orbits Saturn every 13.8 hours from an average distance of 134,000 kilometers (80,150 miles), equivalent to about one-third the Earth-Moon distance, and just 73,000 miles from the Saturnian cloud tops), the 34x31x21-kilometer moon carves out the Encke Gap in Saturn's outermost bright A Ring. After accurately predicting the moon's orbit, Pan was found in 11 images taken by Voyager 2 during its August 1981 flyby. Showalter and colleagues first inferred the tiny moon's presence by the waves it kicked up in the wake of its passage through the Encke Gap. Mark Showalter (then at Stanford University) discovered Pan on July 16, 1990. “Here is 35-km Pan in mind-blowing detail with its unmistakable accretionary equatorial bulge.” Cassini's flyby of Pan, frame by frame. “Nearing its end, Cassini delights again,” says Carolyn Porco (Space Science Institute) on Twitter. NASA's Cassini spacecraft flew just 15,268 miles past the moonlet (closer than the distance to the geosynchronous satellites from Earth) on March 7th. ![]() Appropriately named after the half-man, half-goat satyr from Greek mythology, Pan is nestled in the Encke (pronounced EN-key) Gap within Saturn's A ring. Who ordered that? The universe served up a piece of astro-pareidolia last week, when humanity got its first closeup look at Saturn's tiny moon Pan. NASA / JPL-Caltech / Space Science Institute doi: 10.1016/j.icarus.2010.01.025.Cassini gave us a good look a Saturn's moon Pan last week. "Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission" (PDF). ![]() "The orbits of Saturn's small satellites derived from combined historic and Cassini imaging observations". "Satellites of Jupiter and Saturn" (naming the moon). Archived from the original (discovery) on. (Subscription or participating institution membership required.) Because the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well. Ītlas is significantly perturbed by Prometheus and to a lesser degree by Pandora, leading to excursions in longitude of up to 600 km (~0.25°) away from the precessing Keplerian orbit with a rough period of about 3 years. This would mean that for any additional particles impacting the equator, the centrifugal force will nearly overcome Atlas's tiny gravity, and they will probably be lost. In fact, the size of the equatorial ridge is comparable with the expected Roche lobe of the moon. The most likely explanation for this unusual and prominent structure is that ring material swept up by the moon accumulates on the moon, with a strong preference for the equator due to the ring's thinness. High-resolution images taken in June 2005 by Cassini revealed Atlas to have a roughly spherical centre surrounded by a large, smooth equatorial ridge. In 2004 a faint, thin ring, temporarily designated R/2004 S 1, was discovered in the Atlantean orbit. However, now it is known that the outer edge of the ring is instead maintained by a 7:6 orbital resonance with the larger but more distant moons Janus and Epimetheus. It is also designated Saturn XV.Ītlas is the closest satellite to the sharp outer edge of the A ring, and was long thought to be a shepherd satellite for this ring. In 1983 it was officially named after Atlas of Greek mythology, because it "holds the rings on its shoulders" like the Titan Atlas held the sky up above the Earth. Atlas is an inner satellite of Saturn which was discovered by Richard Terrile in 1980 from Voyager photos and was designated S/1980 S 28.
0 Comments
Leave a Reply. |