Saturn's atmosphere-shrouded moon Titan is dotted with methane lakes, giving it a geography like Saskatchewan or the Great Lakes region in the US. But why are all the lakes grouped in the northern hemisphere of the moon?

Scientists at Caltech think they may have uncovered the reasons for Titan's extremely odd lake arrangement. Data gathered by the Cassini orbiter showed 20 times more area in the Northern extremities were covered by liquid ethane and methane, when compared to the South. The researchers, headed by Oded Aharonson, think that the transport of methane northwards may be due to the elliptical orbit of Saturn, and hence Titan.

Over the course of one Titan year (29.5 Earth years), the Northern hemisphere summer is long and mild, but the Southern hemisphere version is short and intense. That's because in the Southern summer season Titan is around 12% closer to the sun. While this doesn't make a huge difference over the course of a year, it does over a longer time period: It's possible that these uneven seasons result in methane evaporating in the south, drifting northward in the clouds, and then raining prodigiously in the milder north.

Around 32,000 years ago, the situation would have been reversed, with the hydrocarbons traveling Southward instead of North.


This theory is being published in this month's Nature Geoscience. Other possible explanations for the lakes include the idea that there is some (as yet unknown) fundamental difference between the hemispheres. It's also possible the methane transfer happens every season, not gradually.