![]() The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. All images are oriented so that north is up. 16, 2017, at a distance of 17,000 miles (28,000 kilometers) and at a phase angle of 71 degrees. The images of Pan were taken on March 7, 2017, at a distance of 16,000 miles (26,000 kilometers) and a phase angle of 21 degrees. The images of Atlas were acquired on April 12, 2017, at a distance of 10,000 miles (16,000 kilometers) and at a sun-moon-spacecraft angle (or phase angle) of 37 degrees. (The Daphnis image in Figure 1 was colored using the same green filter image for all three color channels, adjusted to have a realistic appearance next to the other two moons.)Ī version of the montage using only monochrome images is also provided ( Figure 2).Īll of these images were taken using the Cassini spacecraft narrow-angle camera. Images of Atlas and Pan taken using infrared, green and ultraviolet spectral filters were combined to create enhanced-color views ( Figure 1), which highlight subtle color differences across the moons' surfaces at wavelengths not visible to human eyes. Pan's equatorial band is much thinner and more sharply defined, and the central mass of Atlas (the part underneath the smooth equatorial band) appears to be smaller than that of Pan. ![]() Two differences between Atlas and Pan are obvious in this montage. This montage of views from NASA's Cassini spacecraft shows three of Saturn's small ring moons: Atlas, Daphnis and Pan at the same scale for ease of comparison. Because the orbits of Prometheus and Pandora are chaotic, it is suspected that Atlas's may be as well.English: PIA21449: Small Wonders (color image) 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. Atlas 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.
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