Twisted Disks

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Science  06 May 2011:
Vol. 332, Issue 6030, pp. 672-673
DOI: 10.1126/science.1205672

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Astrophysical disks come in many sizes but, as vertically thin rotation-supported systems, are all susceptible to both external perturbations and internal instabilities. One spectacular form of deformation is vertical bending. For decades, it has been clear that many galactic disks, including our own Galaxy (1), are warped. This manifests as up and down bends of the outer disks of edge-on galaxies and, in more face-on galaxies, by distortions in the neutral hydrogen velocity fields (2, 3). Warps are also seen in circumstellar dust disks [e.g., β Pictoris (4)] and are hypothesized to be present in accretion disks around massive objects (5). Nevertheless, the most striking twisted disks reside in our solar system. This is vividly demonstrated by Hedman et al. (6) and Showalter et al. (7) on pages 708 and 711 of this issue, analyzing the vertical corrugation patterns in the rings of Saturn and Jupiter with imaging data from the Cassini and Galileo/New Horizon spacecrafts, respectively. The new data confirms the previously suspected (8) vertical undulations in Jupiter's main ring. In Saturn's rings, the coherent pattern extends over hundreds of wavelengths, covering not only parts of the D ring (9) but also the entire C ring with an inferred vertical amplitude on the order of a few meters.