Jupiter's gossamer ring: a refined look.It was only a single photo among the thousands taken by the Voyager 1 spacecraft spacecraft Vehicle designed to operate, with or without a crew, in a controlled flight pattern above Earth's lower atmosphere. Since streamlining is not needed in the high vacuum of this environment, a spacecraft's shape is designed according to its mission (see in 1979 that unexpectedly revealed the presence of the faint ring system of Jupiter (SN: 3/17/79, p. 172). So subtle is it that even in a series of photos deliberately taken by Voyager 2 a few months later, a major portion of the system went undetected until refined computer processing suggested its presence four years later (SN: 11/5/83, p. 295). This was Jupiter's "gossamer" ring, the outermost out·er·most adj. Most distant from the center or inside; outmost. outermost Adjective furthest from the centre or middle Adj. 1. portion of the system, and now a group of researchers has published a version of the photo that most clearly confirms its presence. The gossamer ring at first went unnoticed because of its faintness in early versions of images made with Voyager's vidicon vid·i·con n. A small television camera tube that forms a charge-density image on a photoconductive surface for subsequent electron-beam scanning. [vid(eo) + icon(oscope).] camera system. With a vidicon, even a photo of the plain dark sky -- or one made with the camera's shutter (1) An opaque window that is moved in one direction to let light in and in another to close off the light. In fixed-lens cameras, one shutter often suffices for aperture and speed. completely closed -- never produces an evenly black image, because of variations in the vidicon's response. A standard part of the processing of spacecraft vidicon images is therefore to subtract A relational DBMS operation that generates a third file from all the records in one file that are not in a second file. this variation, called a "dark current." The change is often a small one, making little difference except to images of extremely faint features. And Jupiter's gossamer ring, says Mark Showalter of Cornell University Cornell University, mainly at Ithaca, N.Y.; with land-grant, state, and private support; coeducational; chartered 1865, opened 1868. It was named for Ezra Cornell, who donated $500,000 and a tract of land. With the help of state senator Andrew D. , is about 95 percent fainter than the also rarefied rar·e·fied also rar·i·fied adj. 1. Belonging to or reserved for a small select group; esoteric. 2. Elevated in character or style; lofty. rarefied Adjective 1. "bright" ring just inside it. Using a refined dark-current value, however, makes the gossamer ring readily apparent, Showalter and his colleagues report in the Aug. 8 NATURE. From the outer edge of the "bright" ring, about 129,000 kilometers from Jupiter's center, the gossamer ring extends to about 210,000 km, though its outer edge is unclear. The clarified view of the gossamer ring has already affected NASA's next Jupiter mission, called Galileo, which will not arrive until 1988. Galileo will send a probe into the Jovian atmosphere, but the possibility of damage to the probe's heat shield has prompted officials to double the distance from Jupiter at which it penetrates the plane of the rings. |
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