Astronomy

Cloudy Down South

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Science  09 Apr 2010:
Vol. 328, Issue 5975, pp. 139
DOI: 10.1126/science.328.5975.139-a
CREDIT: ISTOCKPHOTO (INSET) VOYAGER PROJECT/NASA

Neptune receives much less radiation from the Sun than either Jupiter or Saturn. Like these two large planets, though, it has a meteorologically active atmosphere, with clouds, storms and possibly a global circulation pattern. Most of Neptune's clouds evolve on a time scale of hours. One cloud, however, has appeared to persist since at least 1989, when it was first detected by the spacecraft Voyager 2. This cloud is located within a few degrees of the south pole, where the troposphere is known to be warmer and where, by analogy with Saturn's south polar environment, researchers suspect that a vortex may exist. Using the Keck Telescope in Hawaii, Luszcz-Cook et al. observed Neptune's south pole in the near-infrared, thereby probing the upper and lower troposphere. Images taken over 3 days in July 2007 show the south polar cloud splitting in two and then coming together again. The altitude observed is consistent with cloud formation due to upwelling and condensation of methane gas. Thus, rather than representing a single stable cloud, the bright feature observed by Voyager marks a site of persistent cloud activity, which may be related to a Neptunian south polar vortex and an organized circulation pattern.

Icarus 10.1016/j.icarus.2010.03.007 (2010).

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