West, R.A., Griswold, D., and Porco, C. (2003). "Jupiter's Polar UV Great Dark Spot." American Astronomical Society, DPS meeting #35, #45.07.

Jupiter's polar UV Great Dark Spot is an ephemeral but recurring feature first seen in near-UV (240-270 nm) images obtained by the Wide Field camera on the Hubble Space Telescope in October, 1997. A movie made from UV images taken by the Cassini Imaging Subsystem (ISS) in late 2000 (Porco et al., 2003, Science 299, 1541-1547) fortuitously captured the formation of the spot and covered a significant evolutionary phase as the spot took on a size and shape similar to Jupiter's Great Red Spot and then stretched in longitude and developed an angular boundary. Here we analyze images at additional wavelengths from HST and from Cassini ISS. The spot rapidly becomes invisible between 300 and about 440 nm. It is not seen in the 890-nm methane band which is sensitive to stratospheric particles, suggesting that the UV absorption is produced by a gaseous constituent and not an aerosol. As it evolves and drifts in System III longitude it stays centered on the perimeter defining a polar vortex region poleward of about 60 degrees north latitude which is remarkably featureless in the 890-nm methane movie made from ISS images.