Thursday, February 24, 2005

Science Magazine - February 25, 2005

Tomorrow's issue of the journal Science is now online so those with a subscription can read those articles and those that don't can read the abstracts. Mostly this special issue is related to Saturn and data from SOI, but the imaging team has a paper focused on Phoebe and Iapetus (including results from the New Year's Eve flyby). Here are some tidbits from that paper:
  • Phoebe has a mean radius of 106.6 ± 1 km and a density of 1.630 ± .045 g/cm3
  • Layering on Phoebe suggests an oversaturation of impact events as more recent impacts excavate older impact ejecta
  • Iapetus has three large impact basins within Cassini Regio, each with at least suggested central rises.
  • Crater counts performed within the southern portion of the trailing hemisphere confirm the old age of Iapetus' surface as suggested by Voyager.
  • Impact features within the equatorial ridge suggest that it is not the youngest feature on the surface. The lack of bright crater floors within Cassini Regio suggests that the leading hemisphere darkening is a fairly young feature.
  • With regards to the bright/dark albedo asymmetry, Bright southern crater rims, dark northern crater rims, and dark north-trending streams in the bright-dark transition region suggest "long-distance, ballistic" transport of the dark material. This could be due to exogenic or endogenic causes, but the authors tend toward exogenic since a reasonable heat source needed for endogenic venting could not be found.
Update: in another imaging science paper, this time about small satellites and rings, the authors confirm that Polydeuces is in fact a trailing trojan of Dione, librating around a point 68 degrees behind Dione, near the L5 Lagrangian point.


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