1. Proxemy Research, Rectortown, Virginia 20140, USA
2. Department of Earth Sciences, University College London, London WC1E 6BT, UK
3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
4. Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
5. Space Department, Johns Hopkins University Applied Physics Lab, Laurel, Maryland 20723-6099, USA
6. US Geological Survey, Flagstaff, Arizona 86001, USA
7. Wheeling Jesuit University and Planetary Science Institute, Tucson, Arizona 85719, USA
8. Stanford University, Stanford, California 94305, USA
9. Goddard Institute for Space Studies, National Aeronautics and Space Administration New York, New York 10025, USA
10. Observatoire de Paris, 92195 Meudon, France
11. Alenia Aerospazio, 00131 Rome, Italy
12. Facoltá di Ingegneria, 80125 Naples, Italy
13. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
14. Observatoire Aquitain des Sciences de l'Univers UMR 5804, 33270 Floirac, France
15. Universitá La Sapienza, 00184 Rome, Italy
16. Dipartimento Interateneo di Fisica, Politecnico di Bari, 70126 Bari, Italy

Correspondence to: E. R. Stofan^1,2 Correspondence and requests for materials should be addressed to E.R.S. (Email: estofan@proxemy.com).

Abstract

The surface of Saturn's haze-shrouded moon Titan has long been proposed to have oceans or lakes, on the basis of the stability of liquid methane at the surface^{1, 2}. Initial visible³ and radar^{4, 5} imaging failed to find any evidence of an ocean, although abundant evidence was found that flowing liquids have existed on the surface^{5, 6}. Here we provide definitive evidence for the presence of lakes on the surface of Titan, obtained during the Cassini Radar flyby of Titan on 22 July 2006 (T₁₆). The radar imaging polewards of 70° north shows more than 75 circular to irregular radar-dark patches, in a region where liquid methane and ethane are expected to be abundant and stable on the surface^{2, 7}. The radar-dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes, including associated channels and location in topographic depressions. Some of the lakes do not completely fill the depressions in which they lie, and apparently dry depressions are present. We interpret this to indicate that lakes are present in a number of states, including partly dry and liquid-filled. These northern-hemisphere lakes constitute the strongest evidence yet that a condensable-liquid hydrological cycle is active in Titan's surface and atmosphere, in which the lakes are filled through rainfall and/or intersection with the subsurface 'liquid methane' table.

1. Proxemy Research, Rectortown, Virginia 20140, USA
2. Department of Earth Sciences, University College London, London WC1E 6BT, UK
3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
4. Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
5. Space Department, Johns Hopkins University Applied Physics Lab, Laurel, Maryland 20723-6099, USA
6. US Geological Survey, Flagstaff, Arizona 86001, USA
7. Wheeling Jesuit University and Planetary Science Institute, Tucson, Arizona 85719, USA
8. Stanford University, Stanford, California 94305, USA
9. Goddard Institute for Space Studies, National Aeronautics and Space Administration New York, New York 10025, USA
10. Observatoire de Paris, 92195 Meudon, France
11. Alenia Aerospazio, 00131 Rome, Italy
12. Facoltá di Ingegneria, 80125 Naples, Italy
13. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
14. Observatoire Aquitain des Sciences de l'Univers UMR 5804, 33270 Floirac, France
15. Universitá La Sapienza, 00184 Rome, Italy
16. Dipartimento Interateneo di Fisica, Politecnico di Bari, 70126 Bari, Italy

Correspondence to: E. R. Stofan^1,2 Correspondence and requests for materials should be addressed to E.R.S. (Email: estofan@proxemy.com).

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