1. Laboratoire de Planétologie et Géodynamique, UMR CNRS 6112, Université de Nantes, Nantes, 44100, France
2. Institute of Planetary Exploration, DLR, Berlin, 12489, Germany
3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109-8099, USA
4. Lunar and Planetary Laboratory and Stewart Observatory, University of Arizona, Tucson, Arizona 85721-0092, USA
5. US Geological Survey, Denver, Colorado 80225, USA
6. US Geological Survey, Flagstaff, Arizona 86011, USA
7. Istituto di Fisica dello Spazio Interplanetario, CNR, Rome, 00133, Italy
8. Institut d'Astrophysique Spatiale, Université de Paris-Sud, Orsay, 91405, France
9. Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Rome, 00133, Italy
10. Observatoire de Paris, Meudon, 92195, France
11. NASA Ames Research Center, Moffett Field, California 94035-1000, USA
12. Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195-1310, USA
13. Cornell University, Astronomy Department, Ithaca, New York 14853, USA

Correspondence to: C. Sotin¹ Correspondence and requests for materials should be addressed to C.S. (Email: Christophe.Sotin@univ-nantes.fr).

Abstract

Titan is the only satellite in our Solar System with a dense atmosphere. The surface pressure is 1.5 bar (ref. 1) and, similar to the Earth, N₂ is the main component of the atmosphere. Methane is the second most important component², but it is photodissociated on a timescale of 10⁷ years (ref. 3). This short timescale has led to the suggestion that Titan may possess a surface or subsurface reservoir of hydrocarbons^{4, 5} to replenish the atmosphere. Here we report near-infrared images of Titan obtained on 26 October 2004 by the Cassini spacecraft. The images show that a widespread methane ocean does not exist; subtle albedo variations instead suggest topographical variations, as would be expected for a more solid (perhaps icy) surface. We also find a circular structure 30 km in diameter that does not resemble any features seen on other icy satellites. We propose that the structure is a dome formed by upwelling icy plumes that release methane into Titan's atmosphere.

1. Laboratoire de Planétologie et Géodynamique, UMR CNRS 6112, Université de Nantes, Nantes, 44100, France
2. Institute of Planetary Exploration, DLR, Berlin, 12489, Germany
3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109-8099, USA
4. Lunar and Planetary Laboratory and Stewart Observatory, University of Arizona, Tucson, Arizona 85721-0092, USA
5. US Geological Survey, Denver, Colorado 80225, USA
6. US Geological Survey, Flagstaff, Arizona 86011, USA
7. Istituto di Fisica dello Spazio Interplanetario, CNR, Rome, 00133, Italy
8. Institut d'Astrophysique Spatiale, Université de Paris-Sud, Orsay, 91405, France
9. Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Rome, 00133, Italy
10. Observatoire de Paris, Meudon, 92195, France
11. NASA Ames Research Center, Moffett Field, California 94035-1000, USA
12. Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195-1310, USA
13. Cornell University, Astronomy Department, Ithaca, New York 14853, USA

Correspondence to: C. Sotin¹ Correspondence and requests for materials should be addressed to C.S. (Email: Christophe.Sotin@univ-nantes.fr).

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