The Changing Surface of Saturn's Titan: Cassini Observations Suggest Active Cryovolcanism

R. M. Nelson(1), L. Kamp(1), R. M. C. Lopes(1), D. L. Matson(1), S. D. Wall(1), R. L. Kirk(2), K. L Mitchell(1), G. Mitri(1), B. W. Hapke(3), M. D. Boryta(4), F. E. Leader(1) , W. D. Smythe(1), K. H. Baines(1), R. Jauman(5), C. Sotin(1), R. N. Clark(6), D. P. Cruikshank(7) , P. Drossart(9), B. J. Buratti(1) , J.Lunine(8), M. Combes(9), G. Bellucci(10), J.-P. Bibring(11), F. Capaccioni(10), P. Cerroni(10), A. Coradini(10), V. Formisano(10), G Filacchione(10), R. Y. Langevin(11), T. B. McCord(12), V. Mennella(13), P. D. Nicholson(14) , B. Sicardy(8) 1-JPL, 4800 Oak Grove Drive, Pasadena CA 91109, 2-USGS, Flagstaff, 3-U Pittsburgh, 4-Mt. Sac Col, 5- DLR, Berlin, 6-USGS Denver, 7-NASA AMES, 8-U Paris-Meudon, 9-Obs de Paris, 10-ISFI-CNR Rome, 11-U Paris -Sud. Orsay, 12-Bear Flt Cntr Winthrop WA, 13-Obs Capodimonte Naples, 14-Cornell U. Several Instruments on the Cassini Saturn Orbiter have been observing the surface of Saturn's moon Titan since mid 2004. The Visual and Infrared Mapping Spectrometer (VIMS) reports that regions near 26oS, 78oW (region 1) and 7oS, 138oW (region 2) exhibit photometric changes consistent with on-going surface activity. These regions are photometrically variable with time(1). Cassini Synthetic Aperture Rader (SAR) has investigated these regions and reports that both of these regions exhibit morphologies consistent with cryovolcanism (2). VIMS observed region 1 eight times and reported that on two occasions the region brightened two-fold and then decreased again on timescales of several weeks. Region 2 was observed on four occasions (Tb-Dec13/2004 ,T8-Oct27/2005, T10-Jan15/2006, T12-Mar18/2006) and exhibited a pronounced change in I/F betweenT8 and T10. Our photometric analysis finds that both regions do not exhibit photometric properties consistent with atmospheric phenomena such as tropospheric clouds. These changes must be at or very near the surface. Radar images of these regions reveal morphology that is consistent with cryovolcanoes. We conclude that the VIMS instrument has found two instances in which selected regions on Titan's surface became unusually reflective and remained reflective on time scales of days to months. In both cases the area of reflectance variability is large (~100000 sq km), larger than either Loki or the Big Island of Hawaii. This is a strong evidence for currently active surface processes on Titan. Pre-Cassini, Titan was thought of as a pre-biotic earth that was frozen in time. Cassini VIMS and SAR observations combined suggest that Titan is the present day is not frozen solid, and is instead an episodically changing or evolving world. References: [1] Nelson R. M. et al, LPSC 2007 , Europlanets 2007, AGU 2007, EGU 2008, Accepted in Icarus 2008. [2] Lopes et al (this meeting), Stofan et al. Icarus 185, 443-456, 2007. Lopes et al. Icarus 186, 395- 412, 2007. Kirk et al., DPS 2007. Acknowledgement: This work done at JPL under contract with NASA