Ida's moon: not a chip off the old block.Data are still trickling in from last year's photo shoot of the asteroid 243 Ida. The Galileo spacecraft recorded pictures and spectra of this rocky body when the probe flew within 2,400 kilometers of Ida on Aug. 28, 1993. But because its main antenna is crippled, Galileo had to store the images on its tape recorder tape recorder, device for recording information on strips of plastic tape (usually polyester) that are coated with fine particles of a magnetic substance, usually an oxide of iron, cobalt, or chromium. The coating is normally held on the tape with a special binder. and can transmit them only at a painfully slow rate. Images radioed 3 months ago confirmed that Ida has a tiny moon orbiting it, the first satellite of an asteroid ever observed (SN: 4/2/94, p.214). According to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. one theory proposed for the origin of the 1.5-km-wide moon, an object that slammed into Ida some time in the past gouged out enough material to form the orbiting body. But new data from the Galileo flyby fly·by also fly-by n. pl. fly·bys A flight passing close to a specified target or position, especially a maneuver in which a spacecraft or satellite passes sufficiently close to a body to make detailed observations without show that despite similarities in color and brightness, Ida and its moon seem to have different compositions. Galileo's near-infrared mapping spectrometer hasn't examined the mineral composition of Ida's entire surface, but those regions it has looked at consist mainly of the mineral olivine olivine (ŏlĭv`ēn), an iron-magnesium silicate mineral, (Mg,Fe)2SiO4, crystallizing in the orthorhombic system. , with traces of orthopyroxene orthopyroxene Any variety of the mineral pyroxene that crystallizes in the orthorhombic system and contains no calcium and little or no aluminum. Enstatite is an orthopyroxene. . In contrast, the moon's surface appears to have roughly equal mixtures of these two minerals and one other, clinopyroxene clinopyroxene Any variety of the mineral pyroxene that crystallizes in the monoclinic system. Diopside and augite are clinopyroxenes. . The compositional differences "suggest the moon is not a chip off the asteroid," says Galileo investigator Robert Carlson of NASA's Jet Propulsion Laboratory “JPL” redirects here. For other uses, see JPL (disambiguation). Jet Propulsion Laboratory (JPL) is a NASA research center located in the cities of Pasadena and La Cañada Flintridge, near Los Angeles, California, USA. in Pasadena, Calif. But even if Ida and its moon aren't mother and daughter, they are probably kin. Clark R. Chapman of the Planetary Science Institute in Tucson describes a model in which a violent impact broke a large asteroid into myriad fragments, one of which was Ida. A smaller fragment could have been captured by Ida and become its moon. To better estimate Ida's size, scientists have now compared a high-resolution image of the asteroid received last fall with recently relayed images. The newly received images show several views of the rotating asteroid during a 3.3-hour interval. (Ida makes one complete revolution in 4.5 hours.) According to this analysis, the asteroid is about 58 km long and 23 km wide. |
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