Program: GS-2010B-Q-42

We propose using T-ReCS to determine the time dependence of an unexpected compact hot spot in Neptune's stratosphere that is offset from its seasonally hot south pole. Images of Neptune's stratospheric emission in 2003 and 2005 were consistent with the expectation of a warm south pole, the result of decades of continuous solar heating. But in 2006, an unexpected compact hot region was also detected in stratospheric emission at ~70 deg S latitude and rotating with the 12.2-hour period of the local neutral atmosphere. The possibility that his might be a singular event, e.g. a cometary collision, was disproven when we re-discovered it (a posteriori) in single 2007 N-band T-ReCS and 2008 Subaru COMICS acquisition images. Because it is clearly infrequent but not rare, we propose to image Neptune at 12.3 microns to sample several longitudes. This will allow us to determine whether this hot spot is (i) a truly ephemeral phenomenon or (ii) a more permanent feature whose longitude was missed in other 2007 and 2008 images. This will allow us to discriminate among various potential causes of the phenomenon. If detected, we will request DD time to follow up with methane measurements to determine its vertical distribution.