As the second-largest moon in the solar system, Saturn's Titan already boasts a nitrogen-rich atmosphere, dynamic weather that sometimes triggers thunderstorms, mountain vistas, and vast sand seas.

Lake on smoggy Titan

This artist concept shows a mirror-smooth lake on the surface of the smoggy moon Titan.


Now you can add lake-front property.

After circling Saturn for years, the Cassini spacecraft finally has solid evidence that a large, flat area near Titan's south pole is almost certainly liquid ethane. This hydrocarbon-filled lake, nicknamed Ontario Lacus by the mission's scientists, covers roughly 7,800 square miles (20,000 square km), slightly larger than Lake Ontario in North America. It's tantalized the Cassini team ever since the spacecraft's main camera discovered dark polar patches in 2005 while peering through the dense, haze-choked atmosphere using an infrared filter.

Follow-up scans with an onboard radar showed the patches to be dark at radar wavelengths as well — just the sort of signature you'd expect from a fluid pool. But the team had to be cautious about calling it a lake outright because other surfaces could conceivably (though improbably) mimic the visible and radar signatures.

The lake hypothesis reached its splash point last December, when Cassini's visible and infrared mapping spectrometer got a good look at the area during one of several dozen flybys of Titan to date. VIMS analyzed the surface's infrared reflectivity between 2 and 5 microns, using wavelengths at which the atmosphere is transparent. A handful of absorptions in the spectra match the ones expected for liquid ethane. Details of the detective work appear in the July 31st issue of Nature.

Lacus Ontario on Titan

Here's how Lacus Ontario, a lake-like feature near Titan's south pole, looked when viewed by Cassini's imaging radar (false-colored view at left) and by its visual and infrared mapping spectrometer in late 2007.

NASA / JPL / R. Brown and others / Nature

Interplanetary chemists once imagined the surface of Titan to be completely inundated by a hydrocarbon sea. That's because sunlight causes methane gas in the moon's atmosphere to break down and recombine as ethane (along with more complex hydrocarbons). Cassini dismissed the idea of a global ocean soon after arriving, but the Huygens probe that it dropped onto Titan's surface photographed river systems as it descended and plopped onto moist ground.

Over the next two years of its historic Saturn-circling mission, Cassini is expected to make at least two dozen more flybys of Titan. Mission scientists hope to use those passes to map out the full extent of the lake regions and gain a more complete geologic picture of this strange world.


Image of Michael C. Emmert

Michael C. Emmert

August 6, 2008 at 12:42 pm

Thank you for this article. I wonder what might be disolved in this lake? Let's send another probe and find out!

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Image of Bill Luzader

Bill Luzader

August 7, 2008 at 8:45 am

The article about this Titan lake at has an image and refers to the "kidney bean" shaped lake near Titan's South Pole. The Sky & Tel article shows a lake that appears like one of the North Pole irregular shaped lakes. To which lake does the research article refer? The NASA press release did not have a Cassini image of the lake - at least when it was first posted.

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