Agreement at Hotei Regio

Cassini scientists have been debating whether there is ample evidence, or not enough, to conclude that slushy ice volcanoes are erupting today on Saturn’s moon Titan. Authors of a new paper report the area called Hotei Regio, located south of the equator near the continent-size feature Xanadu, shows evidence of having been shaped by cryovolcanism. Even though they find no signs of currently active ice volcanoes, the authors agree that evidence points to such activity having occurred in the recent past.

A large impact may have kicked off the geological processes that have created the Hotei Regio landscape Cassini is observing today. Surface characteristics are identified through analysis of observations taken in visible and infrared wavelengths of light. The data show circular structures across a basin several hundred kilometers wide. The authors of the paper say such structures could have been created when an object crashed into Titan. Such an impact could have created zones of weakness in the crust that would set the stage for later volcanic and tectonic activity focused in that region.

Recent synthetic aperture radar images from Cassini’s radar mapper show a one kilometer- deep (half-mile-deep) depression in the center of Hotei Regio that is filled with what is thought to be cryovolcanic flows that are 100 to 200 meters (300 to 700 feet) thick. The depression is surrounded by higher mixed rough and smooth terrain. Channels in that terrain are thought to have been carved by flows of liquid methane that have streamed down from mountains to the margins of the depression.

In December 2008, other Cassini scientists reported changes in the brightness and reflectance of Hotei Regio viewed in visible and infrared wavelengths of light. Those changes were thought to be possible evidence of new material on or near the surface erupting from an ice volcano. The authors of the new paper, however, don’t agree that those observations are evidence of ongoing eruptions on the surface. Instead, they find that the low-resolution visible and infrared spectrometry of the region, acquired through Titan’s aerosol-laden atmosphere, would have produced results that were confused with active cryovolcanism.

They write that while the evidence points to geologically recent volcanic activity at Hotei Regio, “we conclude that the VIMS observations to date do not provide compelling evidence for Cassini actually having witnessed ongoing volcanic activity in Hotei Regio.”

The Cassini team continues to collect, analyze and debate Titan findings, but all agree that the spacecraft’s instruments are revealing Titan as a rapidly evolving object that is providing a new window on the evolution of Earth-like bodies.

This Cassini Science League entry is an overview of a science paper authored, or co-authored, by at least one Cassini scientist. The information above was derived from or informed by the following publications:

1) L. Soderblom (U.S. Geological Survey (USGS), Flagstaff, Arizona); R.H. Brown, J.M.Soderblom (University of Arizona, Tuscon); J.W. Barnes (University of Idaho, Moscow); R.L. Kirk (USGS, Flagstaff); C. Sotin (JPL); R. Jaumann (DLR, Institute of Planetary Research, Berlin, and Freie University, Berlin); D.J. Mackinnon USGS, Flagstaff); D.W. Mackowski (Auburn University, Alabama); K.H. Baines, B.J. Burati (JPL), R.N. Clark (USGS, Denver, Colorado); P.D. Nicholson (Cornell University, Ithaca, New York) Icarus ,Volume 204, Issue 2, December 2009, Pages 429-44610-618

2) “Cassini RADAR images at Hotei Arcus and western Xanadu, Titan: Evidence for geologically recent cryovolcanic activity,” S.D. Wall, R.M. Lopes (JPL); E.R. Stofan (Proxemy Research, Bowie, Maryland); C.A. Wood (Center for Educational Technologies, Wheeling Jesuit University, Wheeling, West Virginia); J.L. Radebaugh (Department of Geological Sciences, Brigham Young University, Provo, Utah); S. M. Hörst (University of Arizona, Tucson); B.W. Stiles; R.M. Nelson, L.W. Kamp, M.A. Janssen(JPL); R.D. Lorenz (Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland) J.I. Lunine (University of Arizona, Tucson); T.G. Farr, G. Mitri (JPL); P. Paillou (Observatoire Aquitain des Sciences de l'Univers, Université de Bordeaux, France) F. Paganelli (Proxemy Research), K.L. Mitchell (JPL), Geophysical Research Letters, Vol. 36, L04203, February 24, 2009

3) “VIMS spectral mapping observations of Titan during the Cassini prime mission,” Jason W. Barnes Department of Physics, University of Idaho, Moscow); Jason M. Soderblom, Robert H. Brown (University of Arizona, Tucson), Bonnie J. Buratti (JPL); Christophe Sotin, Kevin H. Baines (JPL); Roger N. Clark (U.S. Geological Survey (USGS), Denver, Colorado); Ralf Jaumann (Institute of Planetary Research, Berlin, Germany); Thomas B. McCord (Bear Fight Center, Winthrop, Washington); Robert Nelson (JPL); Stéphane Le Mouélic (University of Nantes, France); Sebastien Rodriguez (Centre d’ètude de Saclay, DAPNIA/Sap, Centre de l’Orme des Merisiers); Cedex, France); Caitlin Griffith, Paulo Penteado (University of Arizona, Tuscon); Federico Tosi (Centre de l’Orme des Merisiers); Karly M. Pitman (JPL); Laurence Soderblom (USGS, Flagstaff, Arizona), Katrin Stephan (Institute of Planetary Research, Berlin, Germany); Paul Hayne (UCLA, Los Angeles, California); Graham Vixie (University of Idaho, Moscow); Jean-Pierre Bibring, Giancarlo Bellucci Centre de l’Orme des Merisiers); Fabrizio Capaccioni, Priscilla Cerroni Istituto di Astrofisica Spaziale e Fisica Cosmica, Consiglio Nazionale delle Richerche, Rome, Italy); Angioletta Coradini (Centre de l’Orme des Merisiers); Dale P. Cruikshank (NASA Ames Research Center, Mountain View, California); Pierre Drossart (Observatoire de Paris, Meudon, France); Vittorio Formisano (Centre de l’Orme des Merisiers); Yves Langevin (Université de Paris-Sud, Orsay, France); Dennis L. Matson (JPL); Phillip D. Nicholson USGS, Denver) and Bruno Sicardy (Observatoire de Paris, Meudon), Planetary and Space Science, Volume 57, Issues 14-15, December 2009, Pages 1950-1962

4) “Nature of the 2.8-µm window in Titan’s atmosphere and effects on detection of
surface reflectance characteristics,” P. Hayne (Bear Fight Center, Winthrop, Washington, and UCLA) and T. B. McCord (Bear Fight Center), European Planetary Science Congress Abstracts, Vol. 4, EPSC2009-173-1, 2009

5) “Analysis of a cryolava flow-like feature on Titan,” L. Le Corre, S. Le Mouélic (University of Nantes, France); C. Sotin (JPL); J.-P. Combe (Bear Fight Center, Winthrop, Washington); S. Rodriguez (CEA Orme des Merisiers, France); J.W. Barnes (University of Idaho, Moscow); R.H. Brown (University of Arizona, Tuscon); B.J. Buratti (JPL); R. Jaumann (DLR, Institute of Planetary Research, Berlin, Germany); J. Soderblom (University of Arizona); L.A. Soderblom (U.S. Geological Survey (USGS), Flagstaff, Arizona); R. Clark (USGS, Denver, Colorado); K.H. Baines (JPL) and P.D. Nicholson (Cornell University, Ithaca, New York), Planetary and Space Science, Volume 57, Issue 7, June 2009, Pages 870-879

6) “Saturn's Titan: Surface change, ammonia, and implications for atmospheric and tectonic activity,” R.M. Nelson, L.W. Kamp, D.L. Matson (JPL); P.G.J. Irwin (Clarendon Laboratory, Oxford, UK); K.H. Baines (JPL), M.D. Boryta (Mount San Antonio College, Walnut, California); F.E. Leader (JPL); R. Jaumann (Institute for Planetary Exploration, DLR, Berlin, Germany); W.D. Smythe (JPL), C. Sotin (University of Nantes, France); R.N. Clark (U.S. Geological Survey, Denver, Colorado) D.P. Cruikshank (NASA Ames Research Center Mountain View, California); P. Drossart (Observatoire de Paris, Meudon, France); J.C. Pearl (NASA Goddard Space Flight Center, Greenbelt, Maryland); B.W. Hapke (University of Pittsburgh, Pennsylvania); J. Lunine (University of Arizona); M. Combes (Observatoire de Paris, Paris, France); G. Bellucci (Istituto Astrofisica Spaziale Fisica Cosmica (IASF), Rome, Italy); J.-P. Bibring (Université de Paris, Sud-Orsay, Cedex, France); F. Capaccioni , P. Cerroni, A. Coradini, V. Formisano, G. Filacchione (IASF); R.Y. Langevin (Université de Paris, Sud-Orsay, Cedex, France); T.B. McCord (University of Washington); V. Mennella (Osservatorio Astronomico di Capodimonte, Naples, Italy); P.D. Nicholson (Cornell University, Ithaca, New York) and B. Sicardy (Observatoire de Paris, Meudon, France), Icarus ,Volume 199, Issue 2, February 2009, Pages 429-441

-- Mary Beth Murrill, Cassini science communication coordinator