Titan’s Magic Island: Transient features in a Titan sea

Tuesday, 16 December 2014: 11:35 AM
Jason Daniel Hofgartner1, Alexander G Hayes Jr2, Jonathan I Lunine1, Howard A Zebker3, Bryan W Stiles4, Christophe Sotin5, Jason W Barnes6, Elizabeth P Turtle7, Kevin H Baines8, Robert Hamilton Brown9, Bonnie J Buratti8, Roger Nelson Clark10, Pierre Encrenaz11, Randolph L Kirk12, Alice Anne Le Gall13, Rosaly M C Lopes5, Ralph D Lorenz14, Michael J Malaska15, Karl L Mitchell4, Philip D Nicholson1, Philippe Paillou16, Jani Radebaugh17, Stephen D Wall5 and Charles A Wood10, (1)Cornell University, Ithaca, NY, United States, (2)Cornell University, Astronomy, Ithaca, NY, United States, (3)Stanford University, Stanford, CA, United States, (4)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (5)NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (6)University of Idaho, Moscow, ID, United States, (7)JHU Applied Physics Lab., Laurel, MD, United States, (8)Jet Propulsion Laboratory, Pasadena, CA, United States, (9)University of Arizona, Tucson, AZ, United States, (10)Planetary Science Institute Tucson, Tucson, AZ, United States, (11)Observatoire de Paris, LERMA, Paris, France, (12)USGS Grand Canyon Monitoring and Research Center, Flagstaff, AZ, United States, (13)LATMOS Laboratoire Atmosphères, Milieux, Observations Spatiales, Paris Cedex 05, France, (14)JHU / APL, Laurel, MD, United States, (15)Organization Not Listed, Washington, DC, United States, (16)University of Bordeaux 1, Talence, France, (17)Brigham Young University, Provo, UT, United States
Transient bright features, popularly referred to as Titan’s Magic Island, were observed in Cassini Synthetic Aperture Radar (SAR) images of the northern sea, Ligeia Mare, in July 2013 (Hofgartner et al., 2014, Nature Geosci. 7, 493). Images obtained prior and subsequent to the July 2013 detection do not include these bright features. The features are not consistent with ambiguities, scalloping, gain control or edge effects and are not considered to be standard SAR image artifacts. We compared the measured radar cross-sections from the region of the anomalies to a suite of quasi-specular plus diffuse backscatter models and found that this class of models for a permanent structure can be ruled out to 88% confidence. Thus we conclude that the appearance of the features is the result of a transformation and the subsequent non-detections indicate that they were transient. The observational constraints do not permit tides and/or sea level change to be the dominant cause of the transient expression. We suggest that ephemeral phenomena such as surface waves, rising bubbles, and suspended or floating solids best explain these features. Local meteorology could stimulate or enhance these phenomena, but we are unable to constrain its role in the appearance of these transients. These enigmatic features and the waves reportedly detected in Punga Mare (Barnes et al., 2014, Planetary Science, accepted) are likely the first glimpses of dynamic processes that are commencing in the northern lakes and seas as summer nears in the northern hemisphere. It is plausible that they are an expression of the changing seasons and as Titan’s northern hemisphere continues transitioning toward summer they may occur with increased frequency. Ligeia Mare, including the region of the transients, will be observed again during the Cassini Titan flyby on August 21, 2014 and this observation could be diagnostic of the nature of these features. For example, if the transients are waves and waves are detectable at the 12 degrees incidence of the upcoming radar measurements, the predicted increase in wind speeds should result in a higher spatial density of these features.