"Saturn's Titan: Surface Change, Ammonia, and Implications for Atmospheric and Tectonic Activity."
Before the Cassini-Huygens mission began bringing back crucial data about Saturn and its largest moon, Titan, scientists knew very little about the nature of Titan or its hazy atmosphere. It was thought of as a "pre-biotic Earth, frozen in time."
But now, Cassini instruments have provided tantalizing evidence that Titan is currently geologically active, recording what could be a large area where icy ammonia fog vents from the interior and falls to the local surface. The finding indicates that Titan continues to replenish its atmosphere today by outgassing ammonia, which serves as a source for the satellite's nitrogen-dominated atmosphere.
Scientists who recently authored the paper "Saturn's Titan: Surface Change, Ammonia, and Implications for Atmospheric and Tectonic Activity," conclude that distinct changes have occurred on or near the ground over a 73,000 square kilometer-area viewed by Cassini's Visual Infrared Mapping Spectrometer (VIMS) several times over a two-year period. The area in question - twice as large as Hawaii's Big Island -- was found to repeatedly grow and diminish in brightness from 2004-2006.
The scientists say the spectral signature of the reflective material is consistent with ammonia frost, most likely overlying water ice. They theorize that the brightened feature is due to ammonia frost that has vented from the interior and fallen to the surface. The later darkening of the bright frost could be explained by camouflaging from Titan's reddish hydrocarbon rain. Or the bright material could be darkened by weathering, chemical decomposition or evaporation.
The region in question is also comparable to the large volcano, Loki, on Jupiter's Io. "If the entire reflective region is part of the activity, its size is of Krakatoan proportions," says lead author Robert M. Nelson of NASA's Jet Propulsion Laboratory (JPL). "This may be the largest active surface region in the solar system."
Reference: "Saturn's Titan: Surface Change, Ammonia, and Implications for Atmospheric and Tectonic Activity." Icarus, August 4, 2008
Scientists: R..M. Nelson, L.W. Kamp, D.L.Matson (JPL); PG.J. Irwin (Clarendon Lab, U.K.); K.H. Baines (JPL); M.D. Boryta Mt. San Antonio Coll.); F.E. Leader (JPL); R. Jaumann (Inst. for Planetary Exploration, Germany); W.D. Smythe (JPL) C. Sotin (U. Nantes); R. N. Clark (USGS Denver); D.P. Cruikshank (NASA Ames);P. Drossart (Obs. de Paris-Meudon); J.C. Pearl (NASA Goddard); B.W. Hapke (U of Pittsburgh); J. Lunine (U of AZ); M. Combes (Obs. de Paris); G. Bellucci (Inst. di Astrofisica Spaziale, Rome); J.-P. Bibring (Univ. de Paris Sud-Orsay); f. Capaccioni, P. Cerroni, A. Coradini, V. Formisano, G. Filacchione (Instit. Di Astrofisica Spaziale); R. Y. Langevin (Univ. de Paris Sud-Orsay); T. B McCord (U of WA); V. Mennella (Oservatorio Astronomico di Capodimonte); P.D. Nicholson (Cornell U.); B. Sicardy (Obs. de Paris-Meudon)