Enceladus' Between-Stripe Emission

In 2005 data returned by the Cassini spacecraft showed that Enceladus' southern polar region is highly active. The activity is concentrated along four fractures located close to Enceladus' south pole commonly known as tiger stripes, which are also the source of Enceladus' plumes. Accurately constraining the endogenic heat flow from this active region (often call South Polar Terrain, SPT) has proved challenging, and estimates of the SPT total heat flow vary from 5.8 ± 1.9 GW (Spencer et al., 2006) to 15.8 ± 3.1 GW (Howett et al., 2011). Since 2009 Enceladus' active south polar terrain (SPT) has been in winter, which is important for two reasons: 1) it reduces the magnitude of the passive emission and 2) it reduces the difference in passive emission predicted by thermophysical models using a variety of feasible surface parameters. This results in the uncertainty of the passive emission prediction dramatically reducing, from ~4.0 GW in fall, to 0.6 GW in winter. During winter and late-fall Cassini's Composite Infrared Spectrometer (CIRS) took 5 observations of the SPT at a spatial resolution high-enough (<40 km) to put its fields of view between the stripes. We present results from a preliminary study to compare the surface temperatures derived from one swath from one of these CIRS observations (taken in 2015, chosen because it covered all four tiger stripes) to that predicted by a small number of passive models. The results show the observed temperatures are much greater than ones the models predict. Depending on the model, heat flows between 279±48 to 380±36 mW m^-2 are required to explain the difference (2.9±0.5 to 4.0±0.4 GW). These are huge heat flows (!), but are well within those predicted by terrain formation models, and would explain the discrepancy between the different endogenic emissions determined. These results show Enceladus' interstitial region have endogenic emission and more detailed analysis is required to constrain it.