Navigation bar Locations of visitors to this page
Oded Aharonson


Associate Professor of
Planetary Science

B.S. 1994, Cornell University

M.Eng. 1995, Cornell University

Ph.D. 2002, Massachusetts Institute of Technology


Titan's Lakes

Titan's Lakes

The Cassini spacecraft arrived to Saturn's system in June 2004. Since then Synthetic Aperture Radar (SAR) imaging revealed a vast set of surface features interpreted to be lakes. The lakes appear in various states of filling with liquid hydrocarbons, primarily methane and ethane.

The figure below shows the mapped distribution of lakes. The northern high-latitudes, polewards of 55N exhibit a significantly higher abundance of lakes of all type than the south. In particular, the north is occupied by more than 20 times more lakes than the south by area. An explanation for this surprising asymmetry is required.

We propose the following explanation. In addition to seasonal methane transport, that's known to occur over the Titan year (~29 Earth years), there is a component of the hemispheric flux of hydrocarbons that results from the orbital asymmetry. Saturn, and hence its satellite Titan, have orbits around the Sun that are eccentric and oblique. During southern summer Titan is close to the sun, and during northern summer it is ~12% further from the Sun. As a result, southern summers are short and intense, while northern summers are long and subdued (an analogous effects have been recognized on Earth and Mars). While the total solar radiation received over a year is symmetric, the seasonal peaks are different. The orbital parameters vary in time, forcing the asymmetry to modulate and alternate between hemispheres.

The figure above illustrates the situation (Image credit: NASA/JPL/Caltech/University of Arizona/Cassini Imaging & Radar Science Teams, mosaic image here, and animation avi files: ver 1 and ver 2). In a reference frame where the closest point to the sun is fixed, the positions of the four seasons circulate over tens of thousands of years timescale. At present, during northern summers (around summer solstice) the seasonal transport is from the south to the north (blue molecules). We propose that in this orbital configuration the difference between evaporation and precipitation is not equal in opposite seasons, there exists net transport averaged over a year from south to north that results from the insolation asymmetry (larger purple molecules).

Interestingly, approximately 32 kyr ago, the situation was reversed. The seasonal transport was similar, but then northern summers aligned with perihelion, the solar peak flux was higher in the north, and the net transport reversed. In this heuristic scenario, the long term transport is towards the less intensely heated pole, but the actual surface liquid accumulation would depend on the complexities of the climate system's evaporation and precipitation properties.

The hypothesis presented here suggests a process analogous to the Earth's (Croll-) Milankovitch climate cycles. On Titan, the mutual tugs of the planets cause orbital variations that alter the solar radiation. These in turn, lead to volatile hydrocarbon transport from pole to pole over tens of thousands of years timscale. On Earth, the Milankovitch theory links the orbital variations and consequent sunlight patterns to climate cycles driving our own dominant volatile - water, in the form of glaciers. Ice sheets redistribute periodically and globally. In both cases we find a record of the process embedded in the geology. (Milankovitch, Milutin (1998) [1941]. Canon of Insolation and the Ice Age Problem. Belgrade: Zavod za Udzbenike i Nastavna Sredstva. ISBN 8617066199.)

More information about this and other research is available in the form of published manuscripts here. This paper's online publication is:

Aharonson O., A. G. Hayes , J. I. Lunine , R D. Lorenz , M. D. Allison, C. Elachi, An asymmetric distribution of lakes on Titan as a possible consequence of orbital forcing, Nature Geoscience, doi:10.1038/ngeo698, 2009