Planetary-scale atmospheric waves that can ripple into formations may be responsible for the giant white arrow that appears on the surface of Titan, Saturn's largest moon, according to new research from scientists at the University of California, Los Angeles.

The study, published in the Aug. 14 online edition of the journal Nature Geoscience, used a global circulation model of Titan to discover how the Texas-sized cloud formation developed into its recognizable shape. The model was used to demonstrate how atmospheric waves affect the moon's weather patterns, leading to - in some cases - a "stenciling" effect that can make a cloud resemble a noticeable pattern or shape.

Jonathan L. Mitchell, an assistant professor of earth and space sciences and atmospheric and ocean sciences at UCLA who also led the research group, said the atmospheric waves can be likened to a wine glass ringing with a pure resonant tone.

"Individual clouds might 'ring the bell,' so to speak, and once the ringing starts, the clouds have to respond to that vibration," he said.

Scientists have learned more about Saturn and its moon in recent years after the launch of NASA's Cassini Spacecraft, which has been in orbit around the distinctive planet since late 2004. The spacecraft has revolutionized scientists' understanding of Titan, which is the second-biggest moon in the solar system aside from Jupiter's Ganymede and is larger in volume than the planet Mercury.

The clouds resulting from Titan's atmospheric waves can cause precipitation up to 20 times the average seasonal rainfall, which researchers believe could be the key to the shaping of its surface by erosion. That would explain the presence of what appears to be numerous river patterns on the surface of the moon.

While Titan is an alien moon, researchers said it shares many similarities with Earth. The main component of its atmosphere is also molecular nitrogen and water is abundant, although it is frozen in the crust at extremely low temperatures. In addition, like Earth, methane is thermodynamically active in the lower atmospheres, which form rain clouds that are resupplied from surface sources, much like water vapor on our planet.

Researchers hypothesize that Earth may have had an atmosphere like Titan's - with large amounts of methane and limited oxygen - shortly after its atmosphere formed. It is possible that methane provided a necessary greenhouse warming that prevented Earth from staying in a frozen state.

Scientists believe that the similarities between Earth and Titan - which also includes an "all-tropics" weather similar to what is found on Earth's equatorial region - may mean that studying Titan's modern climate may give insight into early Earth's meteorological conditions.

"Our hope is that this may help us understand Earth's weather in a changing climate," Mitchell said. "Titan is like Earth's strange sibling - the only other rocky body in the solar system that currently experiences rain."

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