Cassini sees tropical lakes on Saturn moon

May produce “interesting” molecules like amino acids, the building blocks of life
June 14, 2012
cassini_titan

Saturn's rings lie in the distance as the Cassini spacecraft looks toward Titan and its dark region called Shangri-La, east of the landing site of the Huygens Probe. Areas appear dark to the visual and infrared mapping spectrometer when liquid ethane or methane are present. (Credit: NASA/JPL-Caltech/Space Science Institute)

NASA’s Cassini spacecraft has spied long-standing methane lakes, or puddles, in the “tropics” of Saturn’s moon Titan. One of the tropical lakes appears to be about half the size of Utah’s Great Salt Lake, with a depth of at least 3 feet (1 meter).

The result, which is a new analysis of Cassini data, is unexpected because models had assumed the long-standing bodies of liquid would only exist at the poles.

Where could the liquid for these lakes come from?  “A likely supplier is an underground aquifer,” said Caitlin Griffith, the paper’s lead author and a Cassini team associate at the University of Arizona, Tucson. “In essence, Titan may have oases.”

Understanding how lakes or wetlands form on Titan helps scientists learn about the moon’s weather. Like Earth’s hydrological cycle, Titan has a “methane” cycle, with methane rather than water circulating. In Titan’s atmosphere, ultraviolet light breaks apart methane, initiating a chain of complicated organic chemical reactions. But existing models haven’t been able to account for the abundant supply of methane.

“An aquifer could explain one of the puzzling questions about the existence of methane, which is continually depleted,” Griffith said. “Methane is a progenitor of Titan’s organic chemistry, which likely produces interesting molecules like amino acids, the building blocks of life.”

Global circulation models of Titan have theorized that liquid methane in the moon’s equatorial region evaporates and is carried by wind to the north and south poles, where cooler temperatures cause methane to condense. When it falls to the surface, it forms the polar lakes. On Earth, water is similarly transported by the circulation, yet the oceans also transport water, thereby countering the atmospheric effects.

cassini_images_titan

Images of Titan at three wavelengths that probe the surface (credit: Caitlin A. Griffith et al./Nature)

Some regions could be shallow, ankle-deep puddles. Cassini’s radar mapper has seen lakes in the polar region, but hasn’t detected any lakes at low latitudes.

Ref.: Caitlin A. Griffith et al., Possible tropical lakes on Titan from observations of dark terrain, Nature, 2012, DOI: 10.1038/nature11165