Archiving Titan's surface changes: the global change in 2010

We analyzed 16,000 Cassini ISS (Imaging Science Subsystem) images of Titan in the 935 nm CB3 filter.  The apparent changes during the 13-years of observations are a complex superposition of atmospheric changes, changes due to geometry, and physical surface changes.  Because atmospheric changes dominate and the signal from the surface is attenuated by the atmosphere by about two orders of magnitude, the signal from the surface in single images is too noisy to allow detection of surface changes, except for the largest ones that have been published.

However, when stacking hundreds or thousands of images, good signal-to-noise ratios can be restored, but the challenge lies in the accuracy of stacking since surface data are influenced by the changing atmosphere.  We tried to account for atmospheric effects that create shifts, smear, and attenuation.

Once we use all 16,000 suitable ISS images for stacking, we find that low-contrast surface changes show a richness of types of changes, yet most of them have the same temporal variability:  features stayed constant from 2004 to 2010 and from 2011 to 2017, but changed significantly between both periods.  Three examples are displayed in Fig. 1.  The data are consistent with a sudden change in September 2010, which corresponds to the time of the strongest storm observed during the Cassini period (https://www.nasa.gov/image-article/titans-arrow-shaped-storm/).  Detected surface changes extend over essentially all longitudes and most latitudes that were observed both before and after 2010.  This suggests that the September 2010 storm may have caused global resurfacing on Titan.

We will archive our image products on the Imaging PDS in 2026.  We plan to archive one set of 16,000 images that shows each original  ISS image in about six versions and projections.  We also plan to archive on the order of 100 global mosaics for different time periods so that the timing of detected surface changes can be constrained.

This work was supported by NASA grant 80NSSC21K0866.

 

Fig. 1: The evolution of three selected areas as seen by ISS from 2004 to 2017, centered on 280W 28N (left), 85W 34N (center), and 278W 19S (right), each 1500 km wide.  The color panel at the top shows average images 2004-2010 in blue and 2011-2017 in orange.  Blue and orange areas indicate decreasing and increasing albedo, respectively.  The left panel shows a very dark area with a dark streak toward the northeast until 2010 and toward the north afterwards.  Apparent variations within both time periods may be due to variation in data quality.  The center panel shows the appearance of a bright streak after 2010 that varied and moved.  The right panel shows a region with many changed features between both time periods.  Also, the 2004 image appears to be significantly different from the images 2005-2010.  Note that imperfect calibration can change brightness and contrast, but not the shape of features.