Author/Authors :
Nelson، نويسنده , , R.M. and Kamp، نويسنده , , L.W. and Matson، نويسنده , , D.L. and Irwin، نويسنده , , P.G.J. and Baines، نويسنده , , K.H. and Boryta، نويسنده , , M.D. and Leader، نويسنده , , F.E. and Jaumann، نويسنده , , R. T. Smythe، نويسنده , , W.D. and Sotin، نويسنده , , C. and Clark، نويسنده , , R.N. and Cruikshank، نويسنده , , D.P. and Drossart، نويسنده , , P. L. Pearl، نويسنده , , J.C. and Hapke، نويسنده , , B.W. and Lunine، نويسنده , , J. and Combes، نويسنده , , Christian M. and Bellucci، نويسنده , , G. and Bibring، نويسنده , , J.-P. and Capaccioni، نويسنده , , F. and Cerroni، نويسنده , , P. and Coradini، نويسنده , , A. and Formisano، نويسنده , , V. and Filacchione، نويسنده , , G. and Langevin، نويسنده , , R.Y. and McCord، نويسنده , , T.B. and Mennella، نويسنده , , V. and Nicholson، نويسنده , , P.D. and Sicardy، نويسنده , , B.، نويسنده ,
Abstract :
Titan is known to have a young surface. Here we present evidence from the Cassini Visual and Infrared Mapping Spectrometer that it is currently geologically active. We report that changes in the near-infrared reflectance of a 73,000 km2 area on Titan (latitude 26° S, longitude 78° W) occurred between July 2004 and March of 2006. The reflectance of the area increased by a factor of two between July 2004 and March–April 2005; it then returned to the July 2004 level by November 2005. By late December 2005 the reflectance had surged upward again, establishing a new maximum. Thereafter, it trended downward for the next three months. Detailed spectrophotometric analyses suggest these changes happen at or very near the surface. The spectral differences between the region and its surroundings rule out changes in the distribution of the ices of reasonably expected materials such as H2O, CO2, and CH4 as possible causes. Remarkably, the change is spectrally consistent with the deposition and removal of NH3 frost over a water ice substrate. NH3 has been proposed as a constituent of Titanʹs interior and has never been reported on the surface. The detection of NH3 frost on the surface might possibly be explained by episodic effusive events occur which bring juvenile ammonia from the interior to the surface. If so, its decomposition would feed nitrogen to the atmosphere now and in the future. The lateral extent of the region exceeds that of active areas on the Earth (Hawaii) or Io (Loki).
