Snowball theory may explain Titan’s methane and lakes

New Scientist : Saturn’s largest moon, Titan, has an unusual amount of methane in its atmosphere. Calculations suggest that it would have reacted with other chemicals and disappeared within just a few tens of millions of years, but the moon is 4 billion years old. It is possible that the gas levels are being restored by deposits in the moon, but that raises other issues. The surface of Titan is scattered with liquid lakes that are maintained by the greenhouse effect caused by the atmospheric methane. If the gas is constantly in the atmosphere, then the surface would likely be entirely covered by liquid. Michael Wong at Caltech suggests that Titan may have undergone snowball periods similar to what Earth may have experienced. In the snowball theory, the methane levels are reduced to nearly zero, during which time the moon has a completely frozen surface. But major releases of stored methane periodically warm the surface before the methane levels are again reduced to zero.