Saturn’s eccentric orbit may explain puzzling lake asymmetry on Titan

November 30th, 2009 - 5:44 pm ICT by ANI  

Washington, November 30 (ANI): In a new research, scientists have suggested that the unusually uneven distribution of methane and ethane lakes over the northern and southern polar regions of the Saturn’s largest moon, Titan, may be caused by the eccentricity of the planet’s orbit around the sun.

As revealed by Synthetic Aperture Radar (SAR) imaging data taken by NASA’s Cassini spacecraft, which has been surveying Saturn and its moons since 2004, liquid hydrocarbon-filled lakes in Titan’s northern high latitudes cover 20 times more area than lakes in the southern high latitudes.

There are also significantly more partially filled and now-empty lakes in the north.

Assuming that the asymmetry is not a statistical fluke, scientists initially considered the idea that “there is something inherently different about the northern polar region versus the south in terms of topography, such that liquid rains, drains, or infiltrates the ground more in one hemisphere,” said Oded Aharonson, associate professor of planetary science at Caltech.

However, he notes, there are no substantial known differences between the north and south to support this possibility.

According to the seasonal hypothesis, methane rainfall and evaporation vary in different seasons-recently filling lakes in the north while drying lakes in the south.

The problem with this idea, according to Aharonson, is that it explains decreases of about one meter per year in the depths of lakes in the summer hemisphere.

But, Titan’s lakes are a few hundred meters deep on average, and wouldn’t drain (or fill) in just 15 years.

According to Aharonson and his colleagues, a more plausible explanation is related to the eccentricity of the orbit of Saturn-and hence of Titan, its satellite-around the sun.

Like Earth and the other planets, Saturn’s orbit is not perfectly circular, but is instead somewhat elliptical-or eccentric-and oblique.

Because of this, during its southern summer, Titan is about 12 percent closer to the sun than it is during the northern summer.

As a result, northern summers are long and subdued while southern summers are short and intense.

Aharonson and his colleagues think these differences in the characteristics of the seasons could somehow affect the relative amounts of precipitation and evaporation of methane in the hemispheres’ respective summers.

“We propose that, in this orbital configuration, the difference between evaporation and precipitation is not equal in opposite seasons, which means there is a net transport of methane from south to north,” he said.

This imbalance would lead to an accumulation of methane-and hence the formation of many more lakes-in the northern hemisphere. (ANI)

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